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Steam drive: Its extension to thin oil sands and reservoirs containing residual saturation of high gravity crude
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Steam drive: Its extension to thin oil sands and reservoirs containing residual saturation of high gravity crude
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STEAM DRIVE - ITS EXTENSION TO THIN OIL SANDS AND RESERVOIRS CONTAINING RESIDUAL SATURATION OF HIGH GRAVITY CRUDE by FARHAD GHASSEMI A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (Engineering) August 1981 UMI Number: DP28366 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI DP28366 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 UNIVERSITY OF SOUTHERN CALIFORNIA T H E G R A D U A TE S C H O O L U N IV E R S IT Y PARK LO S A N G E LE S . C A L IF O R N IA 9 0 0 0 7 This dissertation, written by Farhad Ghassemi under the direction of his.... Dissertation Com mittee, and approved by all its members, has been presented to and accepted by The Graduate School, in partial fulfillment of requirements of the degree of D O C T O R O F P H I L O S O P H Y Ph , D, f s r 6r H 10 to ray dear parents Ahmad and Zarrin, for their support, to ray wife Syble, for her encouragement and patience, and to my son Ramean, for his inspiration. i i ACKNOWLEDGMENTS I feel fortunate to have had the opportunity to work under the able supervision of Professor Todd M* Doscher, who served as the chairman of my dissertation committee, provided encouragement and support during the most depress ing hours of experimental work, acted as my friend and mentor throughout the course of this study and enriched me with his unique and enormous insight in the area of thermal oil recovery. I am also indebted to other members of my dissertation committee Professors Iraj Ershaghi and Charles J. Hebert for reading the thesis and making many helpful suggestions. In particular I acknowledge the inspiration received from Professor Ershaghi throughout my graduate work at USC. I cherish all the long hours of discussion that we had about my research work. I owe a great debt of gratitude to Professor Lyman L. Handy, the chairman of Petroleum Engineering Department at USC for his keen interest and critical review of this research work and for many years of moral support and encouragements * Professors George V. Chilingar and Yanis C. Yortsos i i i contributed to the success of my graduate work through their excellent teaching and guidance. During the experimental phase of this project, I bene- fitted from the assistance of several graduate students including Metin Karakas, Maximeliano Pineda, Eze Wanorue and Mansour Noushmehr for which I thank them dearly. I also appreciate the help of Dr. Firooz Ghassemi who assist ed me with the computer plotting of the generated results. The financial support for the project was provided by the Husky Oil Operations for which I’m thankful. Finally, I want to thank my dear wife Syble Ghassemi, who helped me with the typing of the draft, and Maria Vargas for her superb drafting. i v TABLE OF CONTENTS Page DEDICATION ......................................... ii ACKNOWLEDGMENTS ................................... i i i LIST OF FIGURES ........................ vii LIST OF TABLES . . x ABSTRACT...... ...... . ............... xi CHAPTER I. INTRODUCTION ................... 1 II. BACKGROUND INFORMATION ............... 9 A. Laboratory Studies .................... 9 1. Unsealed Physical Models ..... 9 2. Scaled Physical Models ..... 10 B. Field Observation of Steam Drive in Thin Sands ....... 15 III. MODEL DESIGN AND CONSTRUCTION _____ . 17 A. Model Design and Bead Pack ....... 17 B. Injection Equipment ................. .. 22 C. Production Equipment and Fluids ...... 25 D. Experimental Procedure ............... 29 IV. SCALING PARAMETERS AND EXAMPLE CALCULATION 33 A. Scaling Factor ........ 34 B. Scaling of Pressure ..... ... 34 C. Scaling of Temperature ...... 35 D. Scaling of Time ... 35 E. Scaling of Flow Rate ........... 36 F. Scaling of Steam Quality ......... 36 G. Scaling of Viscosity Ratio ...... 38 H. Scaling of Permeability ..... 40 I. Scaling of Flow into Steam Generator .. 42 V. RESULTS AND ANALYSIS .................... 46 A. Effect of Reservoir Thickness and Rate. 50 v CHAPTER Page B. Mechanism of Steam Drive in Heavy Oil . 58 C. Effect of Reservoir Fluid Viscosity ... 66 D. Steam Drive for the Recovery of . Waterflood Residual Oil ............ 84 VI. A POSSIBLE ANALYTICAL EXPLANATION FOR THE EFFECT OF RESERVOIR THICKNESS ON STEAM DRIVE EFFICIENCY ..... . .. 92 VII. CONCLUSIONS ........ 103 NOMENCLATURES ...........*................ 108 REFERENCES *____ 111 v i LIST OF FIGURES Figure Page 1 Thermal Papers Published in JPT, SPEJ and AIME Transactions ....... 2 2 Analytical Predictions of Oil/Steam Ratio (after Myhill & Stegemeier) .... 6 3 Numerical Predictions of Oil/Steam Ratio (after Gomaa) ........... 7 4 Schematic Diagram of the Model ....... 18 5 Picture of the Physical Model ..... 20 6 Picture of the Injection Facilities . 23 7 Picture of the Production Fluids ..... 27 8 Picture of Production Facilities...... 28 9 Schematic Diagram of the Model Set-up. 30 10 Picture of the Model Set-up .......... 32 11 Viscosity-Temperature Chart .......... 41 12 Measured and Calculated Glass Beads Permeabilities ....... 43 13 Effect of Injection Rate on Oil/Steam Ratio for Thin Sands ...... 51 14 Effect of Injection Rate on Oil/Steam Ratio for Thick Sands (after Huang) .. 52 15 Comparison of the Oil/Steam Ratios in Thick and Thin Sands at Rates Close to Optimum Rates ........................ 53 16 Comparison of the Observed Oil/Steam Ratios in Practice and Predicted by Analytical Methods ............... 57 v i i Figure Page 17 Vertical Temperature Profile for Run 9 after 0.5 P.V.'s of Steam Injected ... 59 18 Vertical Temperature Profile for Run 9 (Heavy Oil) after 1.0 P.V.'s of Steam Injected .............................. 60 19 Vertical Temperature Profile for Run 9 after 2.0 P.V.'s of Steam Injected ... 61 20 Effect of the Presence of Nitrogen in Steam Drive on Oil/Steam Ratio (after Omoregie) ..................... ...... 63 21 Effect of Injection Rate in Oil Recovery for Thin Sands ....... 65 22 Oil Production Rates for Runs 7, 8, 9. 67 23 Effect of Oil Viscosity on Cumulative Oil Production (after Huang) ......... 68 24 History of the Oil/Steam Ratio for Light Oil (Run 11) .......... 69 25 Vertical Temperature Profile for Light Oil after 0.5 P.V.'s Steam Injected .. 71 26 Vertical Temperature Profile for Heavy Oil after 1.5 P.V.'s Steam Injected .. 72 27 Vertical Temperature Profile for Light Oil after 1,5 P.V.'s Steam Injected .. 73 28 Injection and Production Pressure Behaviors in the Model for Heavy Oil (Run 9) ______ ________ _______ ____ 75 29 Injection and Production Pressure Behaviors in the Model for Light Oil (Run 11) ....... ............. ........ 76 30 Cumulative Oil/Steam Ratio for Runs 11 and 14 ........................... 77 viii Figure Page 31 Oil Recovery for Runs 11 and 14 ...... 78 32 Vertical Temperature Profile for Run 14 after 0,5 P.V.’s Steam Injected ... 79 33 Vertical Temperature Profile for Run 14 after 1,0 P.V. Steam Injected .... 80 34 Oil/Steam Ratio as a Function of Reservoir Fluid Viscosity ............ 82 35 Cumulative Oil/Steam Ratio History for Run 12 (Residual Oil Saturation of 44%) 85 36 Oil Recovery for Run 12 ..... 86 37 Oil/Steam Ratio History for Run 16 (Residual Oil Saturation of 22%) .... 88 38 Vertical Temperature Profile for Run 12 after 0*5 P.V. Steam Injected ... 89 39 Vertical Temperature Profile for Run 16 after 0,3 P.V. Steam Injected .... 90 40 Vertical Temperature Profile for Run 16 after 0.6 P.V. Steam Injected .... 91 41 Dimensionless Relationship between Oil/Steam Ratio and Dimensionless Time ..... 99 i x LIST OF TABLES Table Page 1 List and Comparison of Dimensionless Groups Used in Literature ............ 14 2 Model and Corresponding Prototype Injection Rates ............... 37 3 Model and Corresponding Prototype Steam Qualities ...................... 39 4 Prototype and Corresponding Model Parameters ................. 45 5 Operating Parameters and Initial Conditions for Model Experiments ..... ' 47 6 Corresponding Prototype Parameters for Model Experiments ......... 48 x ABSTRACT The steam drive process has been extensively used in the recovery of moderately viscous crude oils in Califor nia, Venezuela and Canada. This study was conducted to scrutinize the application of the steam drive process for two other reservoir conditions which have not been consid ered attractive in the past. The earliest analytical studies of the steam drive process conceived of the steam drive to create a steam chest which frontally displaces the resevoir fluid. As a result of this assumed mechanism, a marked effect of reser- vior thickness was predicted. However, the results of many field operations have revealed a surprising insensitivity of the oil/steam ratio (the energy balance of the process) to the reservoir thickness. This, together with the re peated observations in field operations that the steam overrides the oil column, has led to the hypothesis that the mechanism by which the steam drive works is different \ than that originally proposed. This study, as well as previously published studies with vacuum scaled physical models, show that the steam drive is a two-fold process. The overriding or channeling xi of the steam results in the heating of the oil at the interface between the oil column and the steam zone, and the heated oil is then displaced by a gas (steam) drive. It would follow from such a mechanism that thickness would have only a minor effect on the resulting oil/steam ratio. The scaled physical modeling described in this work has confirmed this hypothesis. The results obtained in this study confirm the results of an earlier study which showed the efficiency of the steam drive to be dependent on a fractional power of the reciprocal of the viscosity of the crude oil at steam temperature. It was therefore hypothesized that the oil/steam ratio would become very high if the steam drive was applied to a reservoir containing a high gravity, low viscosity crude. Contrary to earlier suggestions by other authors for the use of the steam drive for recovering high gravity crudes, this study shows that the efficiency of steam drive in such a process is not related to the volatility of the high gravity crude, but merely depends upon a high steam injection rate to efficiently displace the crude to a low residual saturation, while reducing the thermal losses from the reservoir. The scaled model studies reported here show that a high rate steam drive is extremly efficient in reservoirs containing low viscosity fluids. Favorable oil/steam ra x i i tios may be achieved in numerous waterflooded reservoirs containing residual saturations of high gravity crudes. This work has not explored the economic feasibility of implementing these novel uses for the steam drive; however, some of the conditions that would have to be met to achieve economic feasibility are discussed. Earlier work with the scaled physical models have shown a high degree of correlation with the results of commercial field developments. This work has extended the use of the scaling procedures to situations where not scaling the reservoir lithology and reservoir fluid inter action may be of significance; hence, confirmation of the results in field pilots and demonstration projects is required. A quasi-theoretical description of the insensitivity of the steam drive process to reservoir thickness where steam overriding occurs has been developed in this work. x i i i CHAPTER I INTRODUCTION The steam drive has by now been well established as a successful means for exploiting the moderately viscous oils found in California reservoirs and in other parts of the world. Of all Enhanced Oil Recovery techniques, steam drive has been the most successful, both economically and technically, for recovering oil. A quick review of published papers related to thermal operations in Journal of Petroleum Technology, Society of Petroleum Engineering Journal, and AIME Transactions reveals that there has always been more attention on steam related works than other thermal techniques, (e.g., In-Situ Combustion), Figure 1. The steam drive was first attempted in the Mene Grande field 1 in Venezuela in the late 50's where its failure gave rise to the use of cyclic steam stimulation for accelera ting the recovery of crude oil from reservoirs containing viscous crudes. However, during the subsequent decade experiments with the steam drive in the San Joaquin Valley of California and in the Athabasca bituminous sands of 1 Technical Papers Published in JPT,SPEJ, AIME 30 o Steam Related Papers ^ Thermal Related Papers 20 1920 1950 I960 1970 1980 YEAR Figure 1. Thermal Papers Published in JPT, SPEJ and AIME Transactions K> Canada proved that it was a viable method for recovering viscous crude and certain bitumens. Today, production in California alone, reported in the 1979 Annual Review of California Oil and Gas Production, as a result of both cyclic steam injection and steam drive operations, is approximately 400,000 barrels of oil a day, or 40% of the State’s total. Recovery efficiency in some mature operations is already well over 50% of the original oil in place and is projected to approach 70%, a value that is achieved in only a few reservoirs that are exploited by conventional technology. Cumulative recovery from reser voirs subjected to steam injection in California is now approaching 1,5 billion barrels of oil. The steam drive has been intensively studied in the Department of Petroleum Engineering at the University of o i i Southern California using scaled vacuum physical models. These studies have resulted in information which appear to be in accord with the results of field operations, e.g., the occurrence of an optimum rate of steam injection, and the dependency of the efficiency of steam drive to the oil viscosity at steam temperature. Conventional analytical models of steam drive do not encompass the effect of such parameters. In the classical analytical derivation of the way in which a steam drive functions,^ attention is focused on 3 the development of a steam zone, which occupies the entire cross-section of the reservoir, and from which oil is assumed to be depleted to some naturally determined resid ual oil saturation. The fact is, however, that the pres sure required to frontally displace a viscous oil bank at an appreciable (economic) rate can rarely be developed in a real reservoir. Reported field results have demonstrated that steam does not displace heavy oil by frontal advancement. In jected steam initialy enters the formation through a de pleted or wet zone, a fracture, or, in unconsolidated formation, a fluidized interval and then migrates to the top of the oil saturated interval. Then steam zone thick ens in a vertical (downward) direction. Even if the ini tial steam entry is not through a depleted zone at the top of the oil section, then the steam soon migrates to the top, because of its very low density compared to the reservoir fluid density, provided a reasonable vertical permeability exists. The amount of oil produced per unit quantity of steam injected is the most important criteria for judging the success of a steam injection project. This is so because the amount of energy used to generate the steam in even the most successful project is overwhelmingly the largest single component of the cost of producing oil by steam 4 injection. Both analytical^ and numerical^ models of the steam drive process predict a significant effect of reservoir thickness on the oil/steam ratio, see Figures 2 and 3. This is due to the fact that when frontal displacement occurs, the heat loss at the cap and base rock is independ ent of reservoir thickness. Hence, the thicker the reser voir, the greater the fraction of the injected heat that is captured within the reservoir and the greater the oil/steam ratio. However, recent reviews of the performance of steam drive operations have indicated that a much lower range of the oil/steam ratios occur in field operations than would be expected from the results of these calculations. The average of seven current and completed steam drive opera tions in thick sands, in excess of 70 ft. and approaching o 200 ft., reported in recent study, is only 0.22 with a standard deviation of 0,06. On the other hand, the average Q— 1 ? oil/steam ratio for four steam drives in thinner sands, v ranging from 18 ft. to 50 ft. is still 0.2, ranging from 0.15 to 0.25. Further, the recovery efficiency from two of these relatively thin sands, viz., Slocum and San Joaquin have been reported to have approached 80%. This study was therefore designed to investigate the reason why the oil/steam ratio appears to be less in actual 5 0.5 r— i —i —i —r | —i —I —i —r 0.4 0 . 0 ' 0 50 100 FORMATION THICKNESS (GROSS, ft) Figure 2. Analytical Predictions of Oil/Steam Ratio (after Myhil and Stegemeier)6 6 o0.5 £ * 0 .4 < LlI feo.3 ° 0 . 2 LU > H: 3 o.i lo o Porosity _ Steam Quality Injection Rate i r 3 5 % /200 1 .5 B /D / Gross Ac.f Net/Gross ^ ✓lOO ' 30 Reservoir Thickness o 1 0 20 30 40 50 60 MOBILE OIL SATURATION, % 70 Figure 3. Numerical Predictions of Oil/Steam Ratio (after Gomaa)7 operation than would be predicted by numerical and analyt ical models, and in addition, why the oil/steam ratio appears to fall within a narrow band of values for reser voirs having a wide range of thicknesses. Further, because of the increasing value of the oil/steam ratio with a decrease in oil viscosity, it was decided to investigate how high an oil/steam ratio could be achieved in the dis placement of high gravity crudes, particularly at residual oil (to waterflood) saturations. Finally a thorough inves tigation of the mechanism by which steam displaces heavy and light crude oils was conducted. Vacuum scaled physical models were used for the exper imental part of this study. Also, attention was focused on developing a simple analytical model, including the gravity override of the steam, to check.the experimental results. 8 CHAPTER II BACKGROUND INFORMATION Extensive reviews of theoretical and experimental studies of the steam drive process for the recovery of crude oil have appeared in recent publications.3* 1 3 , This review will dwell on laboratory studies of the steam drive operation, and case histories of steam drive operations in the field. A. LABORATORY STUDIES 1. Unsealed Physical Models These experiments were conducted in cores and sand packs. Willman et a 1., ^ did some of the pioneering work using linear cores. They reported that oil recovery by steam drive was higher than that of a hot water drive. They concluded that oil was produced as a result of viscosity reduction and thermal swelling. The procedure suggested by these authors for predicting the performance of a steam drive employs the Marx-Langenheim equations^ and, there fore, has the same limitations. The most important limita tions are the frontal displacement of oil by steam, and the correlative assumption of equal heat losses to the cap and 9 base rocks. Results of a laboratory study reported by Ozen 1 ft and Farouq Ali, ° using linear consolidated Berea cores under isothermal conditions, indicated that the steam drive can be an effective process to recover waterflood residual oil. They' reported 61% oil recovery (after 1 P.V, of steam injected) of Venango First Sand Crude of gravity 47° API (viscosity 4 and 0,1 cp. at 80 and 395°F, respectively). i 7 _ p n Others ' reported the recovery of high gravity oil by steam in linear cores. The effect of injection pressure and rate was inves- p 1 pp tigated by Baker * using a radial sand pack. He obser ved considerable gravity override of the steam vapor and that the fraction of injected heat lost to the cap and base rocks is not a function of injection rate. He also found that the steam zone volume is a function of formation thickness, time and rate of injection. The limitations of the foregoing experiments lies in the fact that they are not scaled, and therefore cannot be used for prediction of field performance. 2. Scaled Physical Models When it appeared that the steam drive process could in fact be used for recovering significant quantities of heavy crude oil, the necessity arose for a reliable predic tive tool. Because of the lack ofj^any history of field 10 operations to serve as an analogue or for calibration of numerical models, the design and construction of properly scaled physical models became necessary. Because fluid and heat flow can both be scaled adequately and simultaneously, scaled physical models of the steam drive can be constructed in great detail. Of course, not all relevant reservoir operational parameters can be perfectly scaled over wide operating ranges, parti cularly capillary phenomena and fluid viscosities. Also, it is laborious to attempt to scale reservoir heterogeneties although it is entirely possible to do so. Oil-water interaction, such as emulsification, should it occur in the prototype reservoir, is generally not included although if it were certain that such an effect contributed to the performance of the steam drive, the phenomena could be superimposed on the fundamental scaling operations. Substantial efforts have been made in developing scaling laws for fluid flow and heat flow parameters, which are the fundamental processes in a steam drive operations, and many investigators have proposed scaling laws for the steam drive^3“27 drawing on the work of others who addressed physical scaling of basic reservoir phenomena.28-33 The earliest steam model experiments were performed in rigid containers or in high pressure vessels in which a confining pressure could be applied externally to the flow 11 chamber. In these experiments, temperatures equal to, or approaching, field levels could be achieved. Many investigators have used high pressure physical models for studying the steam drive process, Huygen^ stud ied the effect of oil viscosity, initial oil saturation, and distillation residue on oil recovery in his 1/2 five- spot model using field crude and crushed sandstone, Pursley^ used Pujol and Boberg's^ scaling rules in his 1/8 five-spot model that simulated the reservoir at Cold Lake, Alberta. His high pressure scaled model was constru cted with identical materials to those used in actual reservoirs. He investigated the effect of bottom water, gas cap, permeability, tight streaks, pattern size, steam quality and steam additives. E h r l i c h ^ also used Pujol and Boberg's method to study the Wabasca heavy oil sand in his 1/4 five-spot model using high pressure steam models. High pressure steam (400°F) was injected into the model con structed with bottom water and horizontal barriers to simu late the actual reservoir conditions. Gravity override of steam occurred and was observed to reach a steady state condition after a lenghty period of time* Singhal^? and Lo^ also used Pujol and Boberg’s scaling parameter except for their scaling of mobility as a single parameter, rather than permeability and oil viscosity separately. Van M e u r s ^ 9 showed that if the ratio of latent to sensible heat 12 was properly scaled, comparable model results could be obtained at low temperatures and sub-atmospheric pressures. Vacuum scaled physical models were first introduced by Stegemeier et al.^9 They showed that actual materials from the field need not be used for model construction and the vacuum system was found more representative of the prototype, because the Clausius-Clapeyron relation for thermodynamic equilibrium and the change of oil viscosity with temperature were matched properly. Vacuum scaled models are excellent tools in the study of the steam drive process. They are relatively easy to construct and operate, safer to use and faster to turn around. Initial studies with the vacuum models showed that the results obtained with them paralleled the results ob tained in field operations.3>39 The assumptions employed by most investigators in the development of the scaling laws are by and large the same as the ones listed by Stegemeier et al. A comparison and discussion of the different scaling laws in the literature o has been done by Doscher, et. al. (See Table 1). They developed scaling parameters that differ slightly from Stegemeier because they used similarities in an integral form, as shown by Yortsos,1 *0 rather than differential forms as did Stegemeier, Doscher et al,,1 * used scaled vacuum physical models 13 TABLE 1 LIST AND COMPARISON OF DIMENS IONLES S GROUPS USED IN THE LITERATURE (Original forms are rearranged to comparable bases) Parameter Scaled Pujol & Boberg Niko & Troost Stegemeier, Volek & Laumbach This Work AP AP AP . AP P ApgL ApgL ApgL ApgL K, t ho <D(pC)0L2 q(pc)0 K, t K, t K, t . he ^ he t nc (pC) L2 p q C HsHs w (pC)cL2 <J>AS (pC)wL2 q(pc)c ■ q.(pC)w m2l2 qM2 q KhoL K, L he *iSKhcL KhcL $ASKhcLCpC)c f f Lv* s - fsLv fsLv Pw (fsLv+CwAT)^AS Pw (fsLv+CwAT)4)AS s C AT w CwAT C AT ' (pC) AT w K ' c MxAT y p os O S 0 Vs<pC>c f y p s's o f y p s sKo K KApgL(pC)c KApgL(pC) c KApgL(pC)w KApgLM^ y K, <j>AS y K, o he o he y Ku <j)AS (p c) o he v 7 c K KApgL(pC) /V /V O % y K, o no ' vNot used by original t —* -p' authors, but added by Singhal?7 ' w'Permeability scaling, viscosity unsealed. to investigate steam drive performance in a Kern River type heavy oil field. They investigated the effect of injection rate, bottom water, steam quality, oil viscosity and per meability. The optimum rate of 2 B/D per acre-ft. was found for the prototype studied. An optimum rate would not occur if steam displaces oil by frontal advance. The study of steam quality showed that the oil/steam ratio is highly dependent on the quality of steam injected. Also produc tion rate was found to be a linear function of the inverse of the square root of viscosity of oil at steam tempera ture. They showed that prototype permeability of more than 1 Darcy has a minimal effect on the steam drive process. B. FIELD OBSERVATIONS OF STEAM DRIVE IN THIN SAND The commercial success of steam drive process in moderately thick reservoirs (more than 70 ft.) has been reported in the literature.® Wooten^ reported on the suc cessful steam drive project in Loco Field in 18 ft. of sand. Waterflooding and hot waterflooding and in-situ combustion processes were unsuccessful because of high viscosity of the oil (600 cp) and channeling of the air and water. Steam was injected at 900 B/D (equivalent water) for 216 days and was then followed by cold water drive (250 B/D for 176 days) to recover the oil. Results showed that the steam drive portion was successful (59% oil recovery) 15 and the oil subsequently recovered by cold water was only 1% of original oil in place. The average cumulative oil- /steam ratio over the life of the project was 0.2. 1 o Hall et al., reported on the result of the steam drive project for Slocum Field. The reservoir is at 600 ft. and contains 19°API crude (2000 cp. viscosity) and has a permeability of 3.5 Darcies, Because of injectivity prob lems, steam was injected into the water sand adjacent to the bottom-portion of the oil sand. Oil recovery today is approaching 80% of the original oil in place, The average cumulative oil/steam ratio was reported as 0,15, Blevins 1 1 et al., reported on the results of the steam drive pro ject for Inglewood Field. Average sand thickness is 50 ft. and the reservoir has a 1200 cp oil with 14.5 °API gravity. The steam injection rate was reported to be 1000 B/D and vertical sweep efficiency was over 50%. Average oil/steam ratio was reported as 0.25. Steamflood performed in the 1 ? San Joaquin area was reported by Greaser et al. Steam was injected into a 29 ft, sand containing 1000 cp oil having 14.5 °API gravity. Oil recovery was reported as 78% and a steam zone was observed at the top portion of the displacement interval. The latter was determined by the compensated neutron-density log. Average cumulative oil- /steam ratio was 0.25 over the life of the project. 16 CHAPTER III MODEL DESIGN AND CONSTRUCTION The experimental apparatus used for scaled physical modeling of steam floods consists of a triangular glass bead pack, which is operated under vacuum and refrigerated conditions with associated injection and production equip ment , A. Model Design and Bead Pack A simple geometry of one-eighth of a five-spot, 5 acre pattern was chosen for all our studies. The design and construction of the scaled model will be described in terms of this one-eighth of a five-spot pattern. For a perfect five-spot, the boundaries of a one-eighth segment are no-flow boundaries, and therefore it is appropriate to use such a model as representative of total pattern perfor mance. Multiwell models of more complex geometries can be designed in a similar manner. The dimensions of the physi cal model used was 36.4” X 36.4” X 51.5" X 4.25" (thic kness). Figure 4 is a schematic diagram of the model located between the cap and base rock. The right angle triangular pack of 16-18 mesh glass 17 Thermocouple Port ttSSSSSSSH .0625 OO Figure 4. Schematic Diagram of the Model. Coprock - Granite Rubber Sheet M odel-Fiberglass Base rock-G ranite beads is surrounded by a rigid fiberglass frame. The 3/4 inch (thickness) X 4.25 inch (height) boards are cemented by high temperature epoxy to two ’ ’wells" which are machined from fiberglass blocks, Figure 5, The fiberglass sides correspond to the no-flow boundaries. The pattern includes one injector and one producer, each representing 1/8 of a prototype well. A fiberglass board (3/8" thickness) was cemented to the bottom of the model frame as the base. This reduced leakage problems that would have been prone to occur if a teflon film was used as the sealing surface at the top surface of the model. This also facilitated the cleaning of the model which would have been more difficult if a teflon film was used. There is no evidence that this discontinuity engendered any by-passing of fluids, and calculations indicated only a trivial effect on the heat lost to the base rock. A cylindrical chamber, 1 inch diameter, was bored vertically through each well block. A small slit was cut along the axis of the cylindrical chamber at the face contacting the bead pack. The slot width,w, was scaled down from the effective well radius r\by the relation w/r w a: = 2.59, which is a log-linear approximation of the rela tionship between slit width and producing well dimensions. The value of 2.59 was interpolated from the assumed rela- 19 Figure 5. Picture of the Physical Model N> o tion of with respect to log (rbead) corresponding to = 2 rbead. (Average diameter of the glass beads is 0.041 inches and c o = 0.082 inches). Forty two (42) 1/8 inch diameter thermocouples were installed through the model in four different rows each one inch apart, Figure 5. The thermocouples were connected to 2, 30 channel speedomax temperature recorders which prints the temperatures continuously. Glass beads were then packed by uniformly sprinkling beads on the vibrating model frame containing enough water to cover the beads. After filling up the model beads near the top flange of the frame were trimmed so that a teflon film (0.005 inch thick) could be properly cemented over the glass beads to the fiberglass model. The teflon sheet behaves as a sealing boundary when vacuum is applied because it is sucked in by the vacuum and fills up any space that exists between the top surface of the glass bead pack and the teflon sheet. Athin rubber sheet (1/16 inch thickness) was placed between the teflon and the cap rock to act as a gasket for the vacuum system and it also provided the proper seal between the cap rock and the model. The cap rock had a thickness of 5 inches to allow simulation of heat loss to an infinite boundary layer for approximately 10 hours of model time. To secure proper scaling, the experiment was run at 21 an initial temperature of 35°F. This was achieved by putting the model in a meat storage type refrigerator box 8 ft.X 8 ft.X 8 ft. The refrigeration equipment was capable of cool-ing the entire system down to the initial tempera ture (35°F) in about 24 hrs. A thermal controller was used to maintain the model temperature at the desired value. Connections for two flow lines were also made at each well model. Pressure gauges and thermocouples were mounted on the injection and production lines close to the well to monitor the pressure and temperature of the steam during the experiment, B. Injection Equipment This section of the system contained two reservoir tanks for storing distilled water, two deaeration chambers, two injection pumps, two flow meters, a steam generator, two regulating valves, check valves and necessary connec tions, Figure 6. The water was deaerated to prevent corrosion and to eliminate the possibility of air leaking into the system. Steam at a controlled quality was made by mixing the superheated steam by the steam generator with distilled water from the water reservoir. The quality of the saturated steam injected into the model reservoir can be controlled by maintaining constant mass flow rates of the superheated steam at a pre-set temperature (230°F) and 22 Figure 6. Picture of Injection Facilities distilled water at room temperature. These two streams are mixed at a known pressure to get the desired scaled steam quality. As already mentioned the feed water to the steam generator was deaerated while flowing into a vacuum cham ber. A thermocouple and a sensitive pressure gauge were connected to the line at a point after the two streams met to measure the temperature and pressure of the steam before injection into the model. These values are compared to the readings for pressure and temperature at the injector. All the steam lines were carefully insulated. Because of the pressure drop across the steam generator, a pump was re quired to inject steam into the vacuum model. A rotameter with a 10 inch scale was used with each stream to measure the flow rate with an accuracy of about 2%, It was found that the flowmeter response was sensitive to change in temperature and, therefore, it was calibrated before each run. The flow rate for the steam generator and the distil led water was controlled by two needle valves installedat the outlet of each rotameter. These valves were watched closely during the entire experiment and the accuracy of the pre-set rates were checked by measurements of the cumulative volumes injected in given time intervals. In general, it was found that the pre-set rates were reliably 24 maintained. The steam generator was a once-through system. It was a 70 in. long by 1 in. (O.D.), 316 stainless steel tube. A 1/2 inch tubular heater (3000 watts) was mounted inside the 3/4 inch (I.D.) steam generator. All the heated fittings as well as steam generator and injection lines were well insulated. The two ends of the tubular heater were connected to an electronic temperature controller made by Chromalox, which senses the temperature through a thermocouple placed at the outlet of the steam generator. The preset tempera ture of the superheated steam was controlled by this thermocouple. C. Production Equipment and Fluids The production fluid passed through a copper heat exchanger 51 inches long x 3/4 inch (O.D.) copper heat exchanger before entering the collector. Production lines were 316 stainless steel, 3/8 inch (O.D.). The condensor was located inside the refrigerator and tap water flowed counter -current in the annular space of the condensor to cool down any bracking - through steam. It was found that before the breakthrough, the refrigerated viscous oil clogged the production line due to its high viscosity. A heater was wrapped around the heat exchanger to heat the tap water and increase the temperature of the oil and thus 25 insure its fluidity. After steam breakthrough, the heater was turned off and tap water alone was circulated to cool down the production fluids. The oil was produced as an emulsion and the following procedures were employed for measuring the produced oil and water: 1. The produced fluids were collected in 1000 ml. beakers. 2. Demulsifiers were added to break the oil and water emulsion and the clear water was drained and measured. 3. The oil was centrifuged to separate the final drop of water out of the oil phase, and any water collected is added to the previous produced water measured before. Figure 7 summarizes the above three stages from left to right. Emulsion problems have been reported in actual field operations and it was observed in these model studies that as long as steam exists in the reservoir the produced oil is always produced as an emulsion with the produced water. 2 i 1 This is a major problem in field operations. ' The production fluid collector consisted of three flasks positioned in three vacuum chambers between which a 4-way electronic solenoid valve was used to switch from one to another. A 23 cu. ft./min., model 1374 Welch Vacuum Pump was used as the source of the vacuum. Figure 8. The vacuum chambers were connected to the vacuum pump through a conventional cold trap. 26 Figure 7. Picture of the Production Fluids N> Figure 8. Picture of the Production Facilities K> 00 D$B Before each experiment, the entire system -was checked for leaks. This was important since the experiment is operated under vacuum. A bypass route was connected in the lines between the injection and production wells through which a stabilized, constant steam injection rate was established before it was injected to the model. The same route was used for calibrating the flow meters before each run. Schematically, the experimental set-up is shown in Figure 9. D. Experimental Procedure. The following steps describe the basic preparations before each experiment: 1. Model is packed with glass beads. 2. A thin teflon sheet is placed on top of the glass beads, and cemented with high temperature epoxy to the model. A one inch thick glass is placed on top of it, (the glass is used for sealing the epoxy to the model). It takes approximately 24 hours for the epoxy to cure. 3. Injection and production lines are connected, thermocouples are attached and their recording devices are checked. 4. The entire system is checked for possible leaks. 5. Model is saturated with water (under vacuum) and water is displaced by the appropriate viscosity 29 Steam Generator ^heating rod 43- Three Valve Meter Model Packed Beads Water + Distilled Glycol Water ■ i Vacuum 1 1 __1_ Vacuum Chamber Chamber 1 2 I I A — ■0“ — —* i Flow Meter 2 Pump 2 Vacuum Pump Water in | Heat Exchanger Temperature Recorder —• Thermocouple ^ Relief Valve ixi Valve b* Regulating Valve KJ Check Valve □ Pressure Transducer O Vacuum Regulator Vacuum Lines Manifold Valves Water out Removable JI J ' l JI B o tto m s ^ A ,, A ,, M Collection 8 Measuring System Figure 9. Schematic Diagram of the Model Set-Up o oil. 6. The 1 inch thick glass is removed an the 1/16” rubber sheet and the cap rock is placed on top of the model, Figure 10. 7. The above system is refrigerated to 35°F. 8. The flow rate is pre-set and the constant rate of steam injection is established through the by pass system. After saturation and before the actual experiment is initiated, foam glass insulation materials are attached to the exposing model walls to reduce the lateral heat loss of the steam. Steam is passed through the production and injection well to clean any cold oil remaining in the wells, and to pre-heat the production well. Because of high viscosity of oil at room temperature, the oil is warmed in an oil bath to about 120°F and then injected into the glass bead pack by turning on the vacuum pump until the water cut is reduced to a trivial value. The oil saturation can be calculated by material balance. Production lines are cleaned after saturation and before start up to prevent clogging by cold viscous oil. On the average, the time for each experiment including cleaning, refrigeration, and data analysis is two weeks. However, with multiple models, and a larger support staff the experiments could be turned out much more rapidly. 31 Figure 10. Picture of the Model Set-up LO CHAPTER IV SCALING PARAMETERS AND EXAMPLE CALCULATION The scaling laws for vacuum models have been des cribed in detail in the 1 iterature.^9 >3 six principal dimensionless scaling groups were used in scaling the pro totypes of this study. They are: ApP (Khpc)ct Kp0gt fsPsPo > p p > 9 9 Apgl (pc)r (<j)AS0)y0L yQps (fsLy + CwAT)pwqst qwt k^(pc)rAT c { ) A S0L^ In order to have the proper scaling, these dimension- less parameters have to be the same for both model and the prototype. Characteristic quantities of pressure, tempera ture and saturation are used. AP is Pg-Pp, AT is Ts-Tr, ASQ is 1-Sor-SW£. Hence, when scaling these three variables, P,T and saturation, the following groups are the same for model and prototype. P(x,y,z) - Pp T(x,y,z) - T r S(x,y,z) - SQr 33 An example calculation is shown below which shows how model values can be converted to prototype values and vice versa. A. Scaling Factor (y(L)) For one-eighth of a five acre five-spot pattern the distance between the injector and producer is 330 ft. The distance between the same two points in the model is 4.292 ft.; then the Y(L) = 76.9. The thickness of the physical model is 0.3542 ft. which simulates a reservoir 27 ft. in thickness. B. Scaling of Pressure From the relation (P — Pp)p (ApgL)p Y (P) = knowing: (P - Pp)^ (ApgL)j^ = 76.9 LP PP PM = 0.94 1 , then: 6m Y(P) = 72.29 and for prototype production pressure of 50 psia and corresponding model pressure of 5 psia: 1 PM = ------ Pp + 4.308 72.29 34 For prototype injection pressure of 300 psia the cor responding model pressure would be 8.5 psia. C. Scaling From the the Temperature relation (T) = (Tp - Tr)p (Ts - Tr)p (th - (Tg - Tj,)^ knowing: (Tr)p = 75°F, (Tr)„ = 35°F (Ts)p = 417°F (at 300 psia.) <Vm = 1 86°F (at 8.5 psia.) then: Tp - 75 417 - 75 Th - 35 186 - 35 1 Tm = ----- Tp + 1.885 2.265 D. Scaling of Time (Khpc)0t From the dimensionless parameter: — -----— L (pc)r The thermal conductivity of the actual reservoir shale sample above the productive zone as well as the cap rock for the physical model were measured at the Riverside campus of the University of California. ^h^cap Prototype = ^*^9 BTU/ft,/hr/ F ^ c a p Model = 1-13 BTU/ft./hr/°F the above value is the effective thermal conductivity of the cap model in the laboratory which is the combination of 5” granite (k = 1.4 BTU/ft.hr °F) and 1/16” rubber (k = 0.085 BTU/ft.hr.°F) in parallel. Also: 35 (pe)Cp = (pc)oM = 31.7 BTU/ft./hr/°F (po)rM = (pc)rP = 25.9 BTU/ft./hr/°F so from ^h^cP (Pc)cP —* • " " 1 t ? ^h^cM (Pc^cM (pc)CM after substitution: Since there are 525,600 minutes per year, every 85.73 min. in the laboratory corresponds to 1 year of prototype time. E. Scaling of Flow Rate Given prototype and model porosity of 33# and proto type and model initial oil saturation of 90% and residual oil saturation to steam of about 10%. or every 1.488 cc/min production or injection volume/time is equal to 1 B/D for the prototype. Table 2 shows the relationship of 3 prototype injection rates and correspon ding injection rates for the physical model. F. Scaling of Steam Quality From: d>As0)M = <4>As0)p so: = 1.348 x 10-2 ^W 36 TABLE 2 MODEL AND CORRESPONDING PROTOTYPE INJECTION RATES Steam injection qw cc/min. q cc/min. B/D for 5 spot for for Prototype 5 - spot Model 1/8 of 5-spot Model 1000 1488 186 744 1107 138.4 526 783 97.8 37 From: (fgLy + OwAT)pwqgt L3(pC) AT Knowing that at 417°F the latent heat of vaporization for the steam is 810 BTU/pound and the corresponding latent heat of vaporization for the steam at 8.5 psia (model pressure) is 987 BTU/pound; then from r Table 3 lists the different model and corresponding prototype steam qualities. G. Scaling of Viscosity Ratio and kinematic viscosity of steam (v g) p at 4 1 7 0 F = 0.016 x - (cw)M V, the following relation is obtained: (fs)M = 0.3623 (fs)P From: (Po^M ^fs^M ^vs^M ^po^M for 15% prototype steam quality:------- 0.361 and kinema- (U0)p (fs)p ^vs^P (ps^P ... fs M 0.3 x ?0-3 ft2/see at 186°F tic viscosity of steam (v ) 10"3 ft2/sec. then: 38 TABLE 3 MODEL AND CORRESPONDING PROTOTYPE STEAM QUALITY (fs)p, % 100 90 80 75 65 50 20 5 (fs)M» % 36.23 32.60 28.90 27.10 23.50 18.10 7.20 1.8 39 The viscosity ratio of 7.2 is valid for different ^fs^M steam qualities since the _______ is constant. (f s )p Figure 11 shows the best average viscosity data for the Lloydminster Reservoir. From the chart: at 417°F (p0)p = 3.5 cp at 281°F (u0)p = 12 cp at 75°F (p0)p = 2000 cp To obtain the corresponding model oil viscosity the relation t-- \— = 7.2 is used: at 8.5 psia and 186°F, (u0)m = 25.2 cp at 4,0 psia and 152°F, (y0)^ = 86.4 cp at 35°F, (y0)„ = 14,400 cp the above three points are located in Figure 11 and, as shown, the heavy oil used for the scaled model studies was Shell Dutrex 2726 since its viscosity matched with the calculated oil viscosities for the model. H. Scaling of Permeability Km )m (p0)m tp (po^p From: ---= ------- .---- .------ .--- -------- Kp (<j)AS0)p Lp (y0)p tM (p0)m after substitution of the corresponding values: kM = 550 Kp For prototype permeability of 1 Darcy, model permea bility should be 550 darcies. To achieve the desired 40 20000000 VISCOSITY - TEMPERATURE CHART FROM ASTM 000 000 100000 Dutrex 419 Dutrex 2726 Calculated model viscosity iOOOO 1000 500 200 100 50 in u 20 o in 100 200 300 400 500 600 TEMPERATURE, °F Figure 11. Viscosity-Temperature Chart scaled permeability, the average glass bead size was ini tially estimated from the equation reported by Stegemeier, et al.39 K = 74,000 d2 d = Glass beads diameter, cm k = absolute permeability, Darcy and for K = 550 D. the average glass bead size of 0.0339” or 20 mesh size was initially estimated. After the permea bilities of several size glass beads were measured at the Petroleum Testing Services in Los Angeles, Figure 12, glass beads of 16-18 mesh in size were used in this study. I. Scaling of Flow into the Steam Generator The following equation is obtained by the heat balan ce over the steam generator assuming the prototype steam quality of 75% , the superheated steam temperature leaving the steam generator of 230°F, and the prototype injection pressure of 300 psia. wa ^ss " ^s^v ” GwAT wa + wss ^ss " ^wa w„ 1161.3 - (0.271)(987) - 151 = 0.665 wa + wss 1161.3 - 43 For wa + wss of 186 cc/min (1000 B/D prototype injec tion rate), 124 cc /min of distilled water at 75°F was 42 3000 Measured Permeability (Petroleum Testing Service) Calculated Permeability (K=74,000d 2 ) 5 2000 1000 8 12 16 20 24 28 32 36 GLASS BEAD MESH SIZE Figure 12. Measured and Calculated Glass Beads Permeabilities 43 mixed with 62 cc/min of superheated steam at 230°F to achieve the 27.1$ quality control steam in the laboratory. Table 4 lists the model and corresponding prototype scaling parameters. 44 TABLE 4 PROTOTYPE AND CORRESPONDING MODEL Prototype Parameter Lloydminster Reservoir PARAMETERS Model Reservoir Temperature, °F 75 35 Pressure, psia Injection 300 8.5 Production 50 5,0 Sand Thickness, ft. 27 0,354 Permeability, Darcy 1 550 Porosity, % 33 33 Steam Injection Temp. °F 417 186 Initial Gas Saturation, % 2 2 Oil Gravity, °API 14 11 ,8 Steam Quality, % 75 27. 1 Scaling Factor 1 76.9 Flow Rate, (P-B/D, M-cc/min) 1000 186 Time (P-year, M-cc/min) 1 85,7 Pattern Area, (P-acre, M-ft ) 5 4.6 Distance of the Injector to Producer well, ft. 330 4. 29 Thermal Conductivity,BTU/hr.ft• °F a) Overburden 1 09 1 13 b) Underburden 1 1 1 0 Oil Viscosity, cp a) Reservoir Temp. 2000 100000 b) Steam Temp. 3. 8 28 45 CHAPTER V RESULTS AND ANALYSIS Experiments were conducted to investigate the effect reservoir thickness, injection rate and low viscosity fluids on the steam drive process. The same model was used in all the runs. The prototype pattern size, reservoir thickness, time scale, permeability, and porosity were the same for all the runs and are listed in Table 4. Table 5 lists the operating parameters and initial conditions for some of the model experiments, and Table 6 lists the corre sponding prototype values calculated from scaling procedure described in Chapter IV. The first few experiments (run 1 to 4) encountered many difficulties. Most of these problems were associated with establishing steam injection into the model which in these early runs had an extremely high oil saturation (in the order of 95%), The pressure could not be controlled below atmospheric levels when reaching the desired injec tion rate, and rupture of various equipment components occured. This problem parallels that encountered in field operations when attempting to inject steam into reservoirs 46 TABLE 5 OPERATING PARAMETERS AND INITIAL CONDITIONS FOR MODEL EXPERIMENT Run # 7 8 9 11 12 14 16 Injection Rate, cc/min 186 98 138.4 134 140 133.8 144 . * Injection Pressure, psia 8.0 7.5 8.5 7.0 7.0 6.0 6.5 Production Pressure, psia 6.0 5.8 6.0 5.0 4.5 4.8 4.0 Steam Temperature, °F 183 177 186 180 178 180 180 Steam Quality, % 26 26.8 24.5 26.8 24.3 25.6 25.3 Oil Viscosity, cp e 73 °F 100000 100000 100000 24 24 7.3 3.3 @ steam Temp. 28 28 28 3.4 3.4 1.8 1.1 Oil Saturation, % 89 93 92.5 95 44 99 22 Water Saturation, % 4 2 5 5 53 0 77 Gas (Air) Saturation, % 7 5 2.5 0 3 1 1 Model Pore Volume, cc 16462 16455 16334 16582 16558 16448 16655 *Average sustained injection pressure, conditions over a major part of the run after steam breakthrough TABLE 6 CORRESPONDING PROTOTYPE PARAMETERS FOR MODEL EXPERIMENTS Run # 7 8 9 11 12 14 16 Injection Rate, B/D 1000 526 744 720 752 719 774 Injection Pressure, psia 267 231 303 195 195 123 158 Steam Temperature, °F 406 397 417 403 400 381 403 Steam Quality, % 72 74 68 74 67 71 70 Oil Viscosity, cp @ Steam temperature 3.9 3.9 3.9 0.47 0.47 0.25 0.15 Oil Saturation, % 89 93 92.5 95 44 99 22 Water Saturation, % 4 2 5 5 53 0 77 Gas (Air) Saturation, % 7 5 2.5 0 3 1 1 * Calculated prototype values from - p " 00 temperature scaling relationship containing high saturatiions of high viscosity oil and no mobile water. The matter was ultimately resolved by reducing the oil saturation to values of the order of 90% by circulating nitrogen through the oil saturated system. The desaturation by nitrogen helped steam injectivity. Previous work has established the fact that it is only by initiatiing and maintaining a channel for steam communica tion will a successfull steam drive be capable of being sustained in a reservoir containing a high initial oil saturation. A calculation of the flow rate of oil from such a reservoir shows that only a very low and unacceptable injection rate of any fluid can be achieved unless the possibility for some kind of communication between wells exists. In numerical simulations, this problem is overcome by assigning a very high (possibly unwarranted) compressi bility to the formation. Further, any injectivity that is initially achieved due to a low saturation of mobile water or gas may well disappear as oil, initially mobilized by steam, cools down-stream and effectively plugs the initial path for fluid flow. This has been repeatedly observed in physical models (and occasionally in field operations) when a well entrenched permeability channel is not established between injection and production wells. In addition to desaturation by nitrogen injection, it was also found necessary to conduct some limited steam 49 soaking of the production well. The primary purpose of heating up the well and production lines was to prevent plugging during the early period of oil production. A. EFFECT OF RESERVOIR THICKNESS AND RATE Figure 13 shows the results obtained for the 27 foot thick prototype on 5 acre spacing (or for 13.5 foot thick reservoir on 2.5 acre spacing at half the indicated injection rate, or for a 52 foot thick reservoir on 10 acre spacing at double the indicated injection rate) at three different injection rates (runs 7,8,9). The evidence of an optimum injection rate (between 526 B/D and 1000 B/D) is one of the most important features of this Figure. Results indicate that the cumulative oil steam ratio increases to a maximum value (0.15, 0.18, 0,19 for run 7,8,9, respective ly) and starts to decrease afterwards. A comparison of this data with the results obtained earlier for a 70 foot prototype,^ Figure 14, indicates that the optimum steam injection rate is in the same range for both models; it is not dependent on the thickness of the formation. The only major difference between the two reservoirs is the thick ness and the other parameters are similar Figure 15 com pares the performance of the optimum steam injection rates in the two models. (The initial difference in the two runs is due to the fact that in the latter work with the thinner reservoir the initial few hundreths of a pore volumes of 50 CUMMULATIVE OIL/STEAM RATIQ .2 RUN 9 744 B/D 18 - m RUN 8 526 B/D . 16 . 14 RUN 7 1000 B/D . 12 .08 .06 . 04 .02 3 4 2 1 0 STEAM INJECTED. EQUIVALENT WATER. P. V. Figure 13. Effect of Injection Rate on Oil/Steam Ratio for Thin sands 0 .4 0 o h 0.35 < cr ^ 0.30 < £ 0.25 in _j 0 . 2 0 0 lu 0*15 > § 0.10 1 0.05 3 O 0 Figure 14. Effect of Injection Rate on Oil/Steam Ratio for Thick Sands (after Huang)3 1196.4 B/d ^ 657.5 B /d 418 B/d 2393 B/d 1.0 2.0 3.0 4.0 STEAM INJECTED, EQUIVALENT WATER, P.V.'s Cn ho 0.40 p 0.35 < O l. 0.30 uj 0.25 1 — if) _j 0.20 o > H 0.10 < I 0.05 Z> O 0 Figure 15. Comparison of the Oil/Steam Ratios in Thick and Thin Sands at Rate Close to Optimum Rates a 27 foot Reservoir — 72 foot Reservoir 657.5 B/d 4 .0 3.0 2.0 1.0 STEAM INJECTED. EQUIVALENT WATER, P.V.'s L n U) oil that was produced was not attributed to the steam drive). Earlier conclusions reported by Brussel and i i p Pittman^^ based on field observations to the effect that the optimum rate is a function of the reservoir volume (acre feet) of the pattern can probably be attributed to the fact that all patterns had approximately the same thickness. The steam quality used in 70 foot prototype runs averaged 5056 whereas the steam quality for the 27 foot runs averaged 7056. Calculations based on the frontal drive theory 5,43 indicate the oil/steam ratio in the first five years should be somewhat higher for the thick reservoir than that observed in this study. Discounting the effect of steam quality, the results for the two reservoirs are virtually identical. A detailed analysis of past and current results of the model studies as well as field operations indicates that when a steam drive is supported by channeling steam, there should be only a minor effect of reservoir thickness on the performance of steam drive; at least up to the point when 40 or so percent of the crude is recovered. Consider the situation when the initial channel is at the top of the section (steam override). The rate of heat loss to the cap rock and the oil column beneath the steam channel is ini tially independent of the thickness of the oil column, and 54 continues to be so until a significant amount of heat begins to be accumulated in the base rock. Hence, all other conditions being the same, the effect of thickness should not become apparent until the fractional recovery becomes quite high. It should be noted that the perform ance of the reservoir under the influence of channeling steam, as predicted by these results, is not as good as c would be anticipated from frontal advance theory , for reservoirs that are thicker than about 25 ft. but better than that predicted for thinner reservoirs, Figure 13. However, recent reviews of the performance of steam drive operations indicates that a much lower range ofoil/steam ratios occur in field operations than is predicted by calculations based on the frontal advance theory. The range of oil/steam ratio for seven current and completed steam drive operations in thick sands, in excess of 70 ft, and o approching 200 ft., reported in a recent study0 is only 0.22 with a standard deviation of 0,06, On the other hand, the average oil/steam ratio for four steam drive in thinner sands, ranging from 18 to 50 ft. is still 0.2, 9-12 ranging from 0,15 to 0,25. Further, the recovery efficiency from two of these relatively thin reservoirs, viz. Slocum and San Joaquin have been reported to have approached 80%, Referring these results to Figure 16 indicates the domi nance of stratified steam in displacing the crude oil. 55 Further, the field results indicate the absence of any 1 p significant effect of reservoir thickness. Greaserhas reported that the San Joaquin project in the Kern River field, at first blush, performs as well or better than say Canfield or Green and Whittier projects despite the fact that its thickness is somewhat less than half that of the latter two projects. The production in the later life of San Joaquin project is distorted by the steam stimulation of other than the target zones for the drive. Neverthe less, the performance during the first several years, when these zones where not being simulated, is not significantly different than the performance of other thicker zone in the San Joaquin Valley. Figure 13 indicates that the maximum cumulative oil/steam ratio for runs 7,8,9 is between 0.15 and 0.19. This is in accord with the results obtained in field steam operations conducted on thin sands(l8 to 50 ft.) reported above. It should be noted that there probably is some minimum thickness of reservoir sand for which the oil steam ratio will indeed begin to decrease rapidly. This thickness is probably of the same order of magnitude as that of the channel that is initially established by the steam. An analytical argument that lends support to the foregoing explanation of the absence of a significant 56 0.5 ANALYTICAL PREDICTIONS (FROM MYHIL AND STEGEMEIR) > 0.4 0.3 OBSERVED RATIO IN OIL/STEAM PRACTICE 0.22 (Average) 0.16 < 0.2 0.1 0.0 50 100 FORMATION THICKNESS, ft Figure 16. Comparison of the Oil/Steam Ratios Observed in Practice and Predicted by Analytical Methods 57 effect of reservoir thickness on oil steam ratio will be discussed in Chapter VI. B. MECHANISM OF THE STEAM DRIVE IN HEAVY OIL It is certain by now that steam does override the heavy oil column and is not capable of displacing viscous oil by frontal advance. Steam follows the less resistive paths available in the reservoir, viz., through an already depleted zone, a fracture, a high water or gas saturation, etc., and will eventually override the oil column because of the density difference between the steam and the oil. The results of temperature (and therefore steam) distribution surveys for the three runs (7,8,9) indicates that steam overrides the visocus oil, and that little oil is produced before there is substantial heat breakthrough. The results of temperature (and therefore steam) distribution surveys for Run No. 9 after the injection of steam generated from 0.5, 1.0, and 2.0 pore volumes of liquid water are shown in Figures 17, 18, and 19, respec tively. The dark heavy squares show the existence of steam based on temperature and pressure measurements. It is clear that steam has gravitated to the top of the reservoir. Oil is being produced in conjunction with the steam and steam condensate, and is being produced as an emulsion, see Figure 7. 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Vertical Temperature Profile for Run 9 (Heavy Oil) after 1.0 P.V. of Steam Injected O n o FLOW DIRECTION * ■ * t a a a a a a • I 71 •aaa aaaa aaaa aaaa •aaa u t t i m i t i d i i i t t i t i i i i laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa laaaaaaaaaaaaaaaaaa 'aaaaaaat 7->aaaaaaa lataaaaaaaaaaaaaaa taaaaaaaaaaaaaaaaa lataaaaaaaaaaaaaaa taaaaaaaaaaaaaaaaa aaaaaaaaaa a aaaaaa 8 K K X 8 X 8 g C 8 K 8 8 X X 2 8 8 x 8 8 8 8 a 8 * k x k x 8 X 8 8 8 8 8 8 8 8 X 8 8 8 aaaaaa aaa aaa i aais8K8xX8Xit'X!8 8 8X8K&!]iR&8&8&i]tax8K8& aaaaa I a 8 8 M K a a K 8 8 x x x & B K X 8 g g 8 £ g x 8 K f t 8 8 8 a 8 < x M 8 Q > x 3 x x aaa l i s a 8 a g g & 8 8 g x g K g x & 8 R X g & K £ x & g x g x x g t t & M g K g g K x g g aa i 8 8 8 8 8 1 >1 3 a g a X X g g X K K I :.| ub S H 2 ! 8 8 & ut HC40t« 8 1 a * 8,!tiU888X8X8518888888 888(188X888888fcX8««888888 tin I K x c ta a X 'X g & g ix x ia g x g g x K B g x x g x g & x x x & K x x x g u ig x x iiX Q i a [ 8 a g 8 g g . * g 8 8 8 X & g X & g 8 2 5 IX X g g X g X 8 5 iX 8 g a X £ X ; f K 8 g X g 8 • • • • lKagaxxgKgggXKxxx&gggggggggg gcsxgxxxxxxxxx aaa I s x x x i C K x x x g a x x x a a g g K g x K K i s bubo v ix g K & x g g g g g igag&sgxxKxgxxgxxxxxxx ebbfc&b ttn ggggxitgK&xxgg aaaaaaaaaaa* aaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa ai 7-iaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa •aaaaaaaaaaaaaaaaa •aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa 888 X8X5CXM KXXXXXXXX X g Q ig g K X g K I'K XXgRXRggtKKBKX I 8 8 8 8 8 8 X 8 8 8 x x x x t - b o b a bu a 8 x g g x g x x x x K x g g x g K & i!)K K K x ;K 3 a x x g .H g K H g 1 8 8 8 8 8 X 8 8 bud-o bi-bb X / * / X V n X uo axXXXKXXXaKXXXiittKKKKXXt£XK.KXXXXKXljtaA I a a a a a a a t a t v i t d i n - c a a n b x x x x x x x b u a x a x K N a a x a a s a K x x a a x K K K x tK a a K K K a a a a a I * a a « a x a i) i b f t c L o t ' c t b B b x x x x «•> < xx b.i o rx x x js g K g o iK x g x x x x g M x g a b a g jiiiu g g 'a x x H x s ifc x g x »ggggggig bbocoa tfcbhd XXX *»»♦» XX. bo ga&XgggXggXXXXXgKgaKggX&RUgaxOIXg 3SXXXSCXX3 i* a a i taoioi i .'J o i ■ *.'Bbbbt- ix x h u h m ?.x t-b « » iB '» M r.«agjiiiQi«ga«a8K»,3'>gKKX8icisM5 Sib.>8)i)t*«« aa aaa 1 l a x a a a a K a 6 ,;Ub c d c t iiib b x x x n m x x b < i 5 s a g » g « x « 8 g a x 8 g x « g g a « « a ia x R g B K x a 8 j£ H « ,ix K x x x K x x aaaa I MXXB8*8 t(l|juBbo.ideijb XXXX • (»* XX l,b 8 XXXXSt&XXfegXKXlbKfclCi'XK.XaXglSXaXISSaXKXXXXgKSKKrtXXX 1888X88 bbtibHtbd.ibbcd XXXXX ti XXX bB adsBXggga 8888 K KttKtC 88 XKXgM;X«aXXX'X« KX88X 888 888X8 DC 88 III 888 ■ 1 a a a a n f c e u t u b t u b b b o x x x x x x x x x x ■ u a a a a a a 1 1 0 6 * 1 a a a a a a u a a a a a a u a a a K a a a B a a a x a a x a a a a a a a a a a a a a a a a a l * « * b«3t*fifuci.-.b x x x x x x x x < x x x x bt> x * x x x i:bntib eiftH r.b i « 8 a i n 8 8 K ) ( i f i K K U R i K K S t B K R x i i i i a i i a a i i t a u K a x a a a a a 1 a a b o d iii-jt t u b 1 1 .1 x x x x x x x x x x x xx xx x bitj h i k i i i jb (.L -.b fe b & b a tu otixixuaaxoixxgx k k k & 1 i 1 a x g a tt g g g x x xocxax 1 jb b aaa-XBKK ( a b a b b B a b d t X X X x > X X X X X X X X X X X X X t.G <t ZXK KiSr. b b t j o t i b H u t i S c a 8 X 8 8 XiJKK X 8 8 XX o b tifc n *tK ((8 « « » « • • • « b b b t t tf g g g K I b e U b B b t.d fc XXX XX X X X X X X X X XXX X X t»b 8K518KX»'Xa b t.b u b fc J W b b M b R K K i m i K K U b f i t l o H b o b f t X M H ttX a a H * t io U n l iS ( ! « • ! « b u B t.b b t.L jc c ; X X X X X X X X X X X X X X X X X X c c 8 8 8 8 I X B it lt X t b t b d u b b c b b G c 8 8 8 X X K K X 8 X j B 8 B 6 u e S 9 u U S b b t t b d B b b 8 8 8 8 M I b b t H t i a o M X X X X X X X X X X XX X X X X X X X B gfcXXXXXSS X K « b o h b B b b d u o b n t j M I I S K K c - r . d b a b u b d b t . b H b d b b b f ib b f e a b & b 8 X 8 8 8 I t o l id b b t i b f i X x X X X X X X X X X X X X X X X X b e K £ K X 8 x X 8 X X X b c a b t c t c t c t bbc. K X X 8 8 d u u b b b 0 6 B u b o U b t a b e > b b B a b 9 a b b a B B t - iU H 8 8 8 8 8 I G f c b n t a H XX X XXX XXXX XX XXX. XXX b d Kfe'fcSXKXXXXfc* b b u b b B u u b b b B tib 8 8 X L.(‘t r t - : D C f 3 6 t « G y H t 8 f c b 3 t d c d e 6 b . - : e t t t 6 G ' j 8 8 8 8 IfcillBuf-.B XXX X X X X XX XXX X X X X X X X b.i « I £ « K S S M R S S e U B b b b b b fe b t- .B b u t b d i - b b t - b b B b 8 b b e a u & b o d S t 3 B £ y B f if lb 6 e 6 H b U t ) b ( R t Dbiiutod XXX XXXXXXXXX XXXXX < X t h 888888X88888 tubttbai.tbtjbfct btocbtBiTtcbiiybbbtjf.tjt.t.dtMhttjdddGfjyGGf.lJBt'U'i 888 Figure 19. Vertical Temperature Profile for Run 9 after 2.0 P.V.'s of Steam Injected a> It is beleived that the steam drive mechanism for the recovery of heavy oil should be veiwed as two distinct sub processes; (i) The heating (viscosity reduction) of the heavy oil at the interface between the oil column and the overriding steam and (ii) the displacement of the heated oil by a gas drive. Studies in liquid filled systems ^ 3 5 have shown that a sufficiently high velocity of the displacing phase is capable of driving down the residual saturation of the displaced phase to very low values, and there is reason to expect similar results when a gas at high velocity is the displacing phase. This has recently been investigated by 1 4 Omoregie. Figure 20 compares the performance of steam drive of a viscous oil with that in two other identical reservoir situations. In these reservoirs the injection of steam and nitrogen was substituded for the injection of steam alone after one pore volume of steam had already been injected. In run 36 steam and nitrogen were simultaneously injected, and in run 37 slugs of nitrogen were alternated with the steam. Comparing the results of run 36, 37 with the control run 38, it is appararent that oil production is being maintained even though steam injection is curtailed as a result of ancillary effect of the injected inert gas. These results clearly show that in a steam drive operation 62 .35 .30 > > 2 .25 RUN 37 t r 2 s te .20 - RUN 36 _! O UJ > S i . 1 0 3 5 3 O □ ALTERNATING STEAM (900 BWD) AND NITROGEN (500 MSCFD) FROM POINT A A SIMULTANEOUS STEAM (450 BWD) AND NITROGEN (500 MSCFD) FROM POINT'S O CONTINOUS STEAM INJECTION AT 9 0 0 BWD .05 .00 3.0 0 . 0 40 1 . 0 2. 0 CUMULATIVE WATER EQUIVALENT STEAM INJECTED (PORE VOLUMES) cr\ Lo Figure 20. Effect of the Presence of Nitrogen in Steam Drive on Oil/Steam Ratio (after Omoregie)1 the steam is playing the multiple role already described. It is apparent in these runs that there is little contribu tion to the oil production from a hot water zone as others have already observed. ^ 9 ^ When the override of the steam occurs (and before steam breakthrough), the injected heat is being used up in three different ways; (i) heat loss to the cap rock (formation), (ii) heat consumed in the steam zone, and (iii) the heat loss to the oil column below the steam oil interface (much of this heat will later be recaptured as the steam zone extends down wards). During this time the reservoir thickness does not contribute any effect on the performance of the steam drive. The effect is only pronounced after the heat reaches the base rock. After the steam breakthrough, the oil/steam ratio decreases if the initial injection rate is maintained. This is due to the fact that some of the injected heat would be produced through the production well. The higher the injection rate, the higher the heat production. Indeed, comparing the results of Runs 7 and 8 (see Figures 13 and 21) indicates that after the breakthrough of steam (approx imately 0.65 pore volume steam injected) the oil/steam ratio for run 7 (1000 B/D) decreases below the value for run 8 (526 B/D), Although the oil/steam ratio is less, the oil production rate is higher for run 7, Figure 22. This indicates that at lower rate, the resulting velocities of 64 PIL RECOVERY, X OOIP 60 RUN 9 744 B/D 50 RUN 7 1000 B/D RUN 8 526 B/D 40 30 20 10 1 2 0 3 4 STEAM INJECTED, EQUIVALENT WATER, P. V. Figure 21. Effect of Injection Rate in Oil Recovery for Thin Sands Ln the uncondensed steam is insufficient to drive the heated oil. At the optimum rate (Between 526 and 1000 B/D), run 9, the oil steam ratio as well as oil production rate are superior than those of the other two runs. Before the steam breakthrough, the performance of the steam drive is beleived to be proportional to the steam injection rate, C. EFFECT OF RESERVOIR FLUID VISCOSITY In the previous study with the vacuum scaled models 3 it appeared that the oil/steam ratio (therefore the oil production rate) is a function of the viscosity of heavy oil at the average steam temperature (see Figure 23). For moderately viscous oils, it was found (with the limited data available) that the oil/steam ratio is a function of one half power of the reciprocal of the oil viscosity at steam temperature. To investigate the effect of fluid viscosity, several experiments were conducted. The results of one such experiments, run 11, are shown in Figure 24. Injected steam had 26.8 % quality corresponding to 74 % prototype quality. Quality control steam was injected into the model containing 95% oil and 5% water saturations at the rate of 134 cc/min (720 B/D prototype). The model oil viscosity of 3.4 cp. at 160°F (average steam temperature in the scaled model) simulates a prototype oil with viscosity of 0.47 cp. 66 OIL PRODUCTION RATE* B/D 350 300 250 _ 200 _ 150 _ 100 50 f RUN 9 \RUN 7 744 B/D 1000 B/D RUN 8 526 B/D 0 10 20 30 OIL RECOVERY. X OOIP 40 50 60 Figure 22. Oil Production Rates for Runs 7, 8 and 9 0.6 cl; o o 0 . 8 u_ o 2: o b o: Li. Q LU O Z> Q O OC CL Effect of Oil Viscosity 8389/2£2 - 2 3 STEAM INJECTED, (EQUIVALENT WATER), P V ‘s 4 ON 00 Figure 23. Effect of Oil Viscosity in Cumulative Oil Production (after Huang)3 CUMMULATIVE OIL/STEAM RATIO 2.0 1.8 _ OIL SATURATION, % OIL VISCOSITY AT STEAM TEMP.,cp 1.6 . 0.47 1. 4 INJECTION RATE,B/D 720 1.2 INJECTION PRESSURE.psia 195 8 _ RUN 2 1 0 STEAM INJECTED. EQUIVALENT WATER. P.V. Figure 24. History of the Oil/Steam Ratio for Light Oil (Run 11) O '! VO at 400 °F (slightly greater than water would have at the same temperature). A comparison of the results for the low viscosity oils (Figure 24) with those for the high viscosity oil (Figure 13) clearly shows that the displacement of the low viscosity fluid by steam results in a much higher oil/steam ratio. A comparison of the temperature (and therefore steam) distribution in the reservoir when displaceing a viscous crude oil, see Figure 14 and one with a low viscosity, Figure 25, is quite informative. Both figures are after 0.5 pore volumes of (equivalent water) steam injected. Figures 26 and 27, portray the temperature distributions for the heavy and light oil after injection of 1.5 P.V. of steam. It should be noted that with a decrease in viscosity of the reservoir fluid the temperature distribution indicates that the mechanism is gradually taking on the aspect of a frontal displacement. This again should be anticipated since the available pressure can now displace the bank of reservoir fluid. The oil steam ratio should now be expected to approach the value predicted by frontal displacement analysisand indeed it does. An earlier numerical modeling also indicated that the override of the steam decreased significantly when injecting steam into a 70 FLOW DIRECTION ♦ — • ........ i ( . — _• — . ..... - j .. _ - . .. -, - , - - . - ..... -1 - - - f ■ , ~ - i - ,. -. , — i ~ i ♦ 1 ............ I...... ...... 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Vertical Temperature Profile for Light Oil after 0.5 P.V. 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Vertical Temperature Profile for Light Oil after 1.5 P.V.'s Steam Injected "■j u> reservoir that had been waterflooded to a residual oil saturation.1 ^ Analyzing the pressure behavior for the light and heavy oil models provides further supporting evidence for the above arguments. Figures 28 and 29 show the model pressure behavior for run 9 (heavy oil) and run 11 (light oil), respectively. The injection pressure builds up to almost atmospheric pressure (the upper pressure limit for vacuum scaled models) due to the resistance of the heavy oil column. After the communication between the wells are established, the injection pressure stabilizes at 8.5 psia. However, in run 11, since the resistance of the oil is substantially lower, the injection pressure is maintained at 7 psia. throughout the experiments. At even lower oil viscosities (0.25 cp. at 381 °F.) the performance of the steam drive is virtually the same. Figures 30, 31 compare the results of Runs 11 and 14. Steam injection in the latter was 720 B/D. The performance for the two runs, in spite of the viscosity difference, is virtually the same. The temperautre profiles after 0,5 and 1.0 P.V. of steam injected, Figure 32, 33 are still indicative of frontal advencement of the steam. It should be noted that although the oil viscosity has been reduced to 0.25 cp., in run 14, the oil steam ratio after 1.5 P.V. of steam injected is the same for both runs. This indicates that for very light oil reservoirs the 74 PRESSURE, Psia 20 INJECTION PRESSURE PRODUCTION PRESSURE ■A- xx> 00 0.5 1 .5 2 . 0 STEAM INJECTED, (EQUIVALENT WATER), P V 's Figure 28. Injection and Production Pressure Behaviors in the Model for Heavy Oil (Run 9) PRESSURE, Psia INJECTION PRESSURE PRODUCTION PRESSURE 0 . 5 1 . 0 1 . 5 STEAM INJECTED, (EQUIVALENT WATER), P V 's Figure 29. Injection and Production Pressure Behaviors in the Model for Light Oil (Run 11) '■ v j CT\ CUMULATIVE OIL/STEAM RATIO STEAM INJECTED, (EQUIVALENT WATER), P V ‘s Figure 30. Cumulative Oil/Steam Ratio for Runs 11 and 14 100 Run II Run 14 50 STEAM INJECTED, (EQUIVALENT WATER), PV's Figure 31. Oil Recovery for Runs 11 and 14 00 FLOW DIRECTION XXXX X x x x x x x x x x x x x x x x x x x XXXX'iOi XXXXXXX* XXXXXXXX XXXXXXXX XXXXXX X x x x x x x x x x x x x x x x x x x x x x x XX I X I I • HI I I I t I i * t l tut t Hill HI i ♦ I I I H I * IIHIH I H IH H I h KK HI XX hh a t a i th XM b X KftM X K C S i b a aa BX *« BB ■ ■ BB BKB BBK ■ ■■ n s a n a l d KM KB h xx aa d xxx a b KKttiM Bd x k x x aa ob KiXBB I X b BUBB • X 6b BBK a x b xxx aa x b b m b aa ufa 6b aa < l : v i | a < a aaa ub a ( fab x X 6d X aaa aaa aaa aaa aaa aaa a XX bt. 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Vertical Temperature Profile for Run 14 after 1.0 P.V. Steam Injected 00 o oil/steam ratio and oil viscosity relationship described before is not applicable anymore since the displacement has taken on a much more frontal character. Figure 34 compares the oil/steam ratio vs. the oil viscosity at steam temperature for three different situa tions; after 1.5 P.V.'s of steam injected, 0.3 and 0.4 P.V.'s of oil recovered. The black circles are from the previous study in the 70 foot thick reservoir,^ and the data points for the low viscosities are from runs 11 (circles) and 14 (squares) obtained in this study. The existence of three different flow regimes appears to be demonstrated by this graph. At low oil viscosities, less than 1.0 csk. at steam temperature (and therefore only a few centipoises at initial reservoir temperature in these experiments), the efficiency of the steam drive appears to be virtually independent of temperature. In the second region, between 1.0 and approximately 10 csks., the oil- /steam ratio is definitely dependent on the oil viscosity at steam temperature; increasing with a reduction in viscosity. The slope in this region ranges from 0.4 to 0.5, deviating from a value of 1.0 that would indicate laminar flow governed by Darcy’s law. The flow in this region appears to be turbulent and therefore the expanded form of the Darcy’s law^^P* 93) should be used. The oil/steam ratio is proportional to a 81 CUMULATIVE OIL/STEAM RATIO, v/v 10.0 RUN II RUN 14 FROM PREVIOUS STUDY BY HUANG2 |.5 P . V . STEAM INJECTED Q— _ AT 03 RV. OIL RECOVERY «K AT 0.4 RV OIL RECOVERY 0 . 1 1.0 10 100 OIL VISCOSITY AT STEAM TEMPERATURE, CENTISTOKES Figure 34. Oil/Steam Ratio as a Function of Reservoir Fluid Viscosity fractional power (0.4 to 0.5) of the reciprocal of oil viscosity at steam temperature. In the third region, where viscosities are higher than 10 (-) csks. at steam tempera ture, it is hypothesized that the slope of the curve would approach unity. At these high viscosities the flow of the crude is laminar despite the high gas velocities and therefore only a first power dependence on viscosity is exhibited. The performance of the steam drive at very low steam temperature oil viscosities indicates that the displacement is indeed a frontal displacement of the reservoir fluids (oil and water) with the controlling pressure drop in the steam zone itself. As the viscosity increases, a transi tion occours to steam overlay and the oil and steam flow becomes stratified. Apparently, the oil at the these in termediate steam temperature viscosities is flowing, or entrained in the steam flow, in a turbulent manner. As the viscosity changes the oil flow (and therefore the oil steam ratio at a constant steam rate) changes according to a fractional exponent of the reciprocal of the viscosity. As the viscosity increases still further, stratified flow occurs exclusively but because of the still high viscosity of the oil at steam temperature, the oil flow is relatively laminar and the flow rate changes linearly with viscosity. 83 -------------------------------------------------------------- D. STEAM DRIVE FOR THE RECOVERY OF WATERFLOOD OIL RESIDUALS The relationship of the oil steam ratio to oil vis cosity, Figure 24, indicates that a steam drive in a reser voir having a 33% porosity and saturated with water will produce the latter at a reservoir fluid/steam ratio of 0.7 after the injection of one pore volume (equivalent water) of steam. The fluid/steam ratio could be higher if the quality of the injected steam at the sand face is above 65$ and the pressure is less than the prototype 200 psi used in the experiment. If the reservoir is not 100$ saturated with water, but contains a residual, low viscosity crude oil which is displaced more or less in proportion to its saturation with the reservoir; then the resulting oil/steam ratio would be anticipated to be 0.7 x SQr. For residual saturation of 0.25, or greater, the resulting oil/steam ratio would be 0.18, or greater, as high or higher than the oil steam ratio experienced in the steam drive of heavy oils in the San Joaquin Valley. The results of a model experiment with a residual oil satura tion of 44$ of a prototype oil with a viscosity of 0.47 cp. at steam temperature is shown in Figures 35 and 36. It is apparent that the hypothesis that the mobile oil is produced as efficiently as water is confirmed by the results of the portrayed experiment. Figure 36 shows that 84 0.3 RUN 12 752 B/D ce 0 . 2 co 0.0 0 . 0 0.5 1.0 1 .5 20 STEAM INJECTED (WATER EQUIVALENT), PV's Figure 35. Cumulative Oil/Steam Ratio History for Run 12 (Residual Oil Saturatio of 44%) 00 Ln 100 8 0 - RUN 1 2 40 20 00 0.5 1.0 1 . 5 20 STEAM INJECTED (WATER EQUIVALENT), PV's Figure 36. Oil Recovery for Run 12 00 60% of the residual oil is produced at an oil steam ratio of 0.26 after the injection of one pore volume of steam. When the prototype oil viscosity was reduced to 0.15 cp. at prototype steam temperature, the residual oil saturation was reduced to 22% by waterflood (run 16). Steam drive was conducted at 774 B/D with sand face quality of 70%. The results of this experiment are shown in Figure 37. It is clear that at the lower residual oil saturation {22%) steam has recoverd the residual oil even more efficiently. The oil/steam ratio is 0.21 after the recov ery of 32% of the original oil in place and 0.14 after 50$ of the oil is recovered. Temperature distributions for run 12 and 16 indicate that steam is advancing through the model frontally since the oil and water have approximately the same viscosity at steam temperature, Figures 38, 39 and 40. It is very important to note that reaching such high oil steam ratios is dependent both on a suitably high steam injection rate and a sufficiently high porosity. However, the results do not appear to be dependent on distillation effect, as had been suggested by previous workers studying li O 4 C the recovery of residual oil by a steam drive. °» Further, the mere fact that a high oil/steam ratio is realized is not sufficient to indicate that an economic steam drive operation is feasible. 87 03 o 5 DC 2 < UJ \— CO \ _l 0.2 RUN o UJ > 3 2 3 O 0 . 0 20 40 OIL RECOVERY, 60 % 0 . 0 . 1 . 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Vertical Temperature Profile for Run 16 after 0.6 P.V. Steam Injected VO CHAPTER VI A POSSIBLE ANALYTICAL EXPLANATION FOR THE EFFECT OF RESERVOIR THICKNESS ON STEAM DRIVE EFFICIENCY Continued study with the vacuum scaled physical models has confirmed the gravity override of the steam for heavy oil, as it has been reported from the actual field observa tions . Most workers seeking analytic description of the pro cess have not included gravity overrride - a significant phenomenon associated with the steam drive. To date, there is no exact solution incorporating gravity override, A number of investigators have developed approximate solution with a consideration of this steam drive characteristics. Van Lookeren,2 ^ derived analytic formula describing approx imate shape of the steam zone for linear flow, and radial flow around the injection well. His theory as well as Dupuitt^ is based on segregated flow principles. He claimed that the formula checked favorably with the scaled laboratory experimental observtions. Neuman^ also ac counted for gravity override in his steam model. He deter mined the vertical rate of growth of the steam zone by the 92 rate of steam condensation at the overburden and the under lying steam-hot water interface. Using Marx Langenheim type assumptions, he claims good agreement between his predictions and field observations. The immense complexity of the steam drive process has made the development of a complete and final exact solution for the analytical models very difficult. Therefore, all of the analytical models developed to date have some as sumptions and limitations. Analytical treatment of steam drive has been developed mainly for a frontal advance of steam zone, with a few exeptions mentioned above. This is in fact not true in mostly all the cases. Field results have shown that steam will override the oil column or chose a less resistive path like a fracture or a water layer at the top or bottom of the formation. Various aspects of the process have been studied previously; however, the effect of the moving boundry on upward or downward heat loses has not been taken into account. Also the effect of specified sand thickness has not been investigated deeply. A simple analytical model has been developed that accords with the experimental observations. In preparing the analytical model the following assumtions have been made: 1. The rate of heat injection is constant. 93 2. The rate of steam fall is constant. 3. Thermal properties of the cap rock, base rock and the formation is identical. 4. There is no heat loss in horizontal direction. 5. The injected heat is used to raise the oil bearing formation to steam temperature. 6. Heat movement upward and downward the steam zone is by conduction. 7. As steam zone advances to the formation each element of the contacted area is exposed to steam instantaniously. In many heavy oil reservoirs, because of the low oil viscosity, it is necessary to have a horizontal fracture to provide the initial path for the steam. Letfs assume there is a fracture of negligible thickness at the top of the formation. The heat injected is being used up in three different ways: (i) the cap rock, (ii) in the reservoir already raised to steam temperature, (iii) in the oil column (and eventually the base rock) beneath the moving oil/steam interface. The accumulation for the first and third categories occurs by conduction, whereas convection is responsible for ultimately bringing the depleted sand up to steam temperature. An analytical expression for the heat loss at a moving boundary (the falling oil/steam interface in our system) 94 has been developed by Carslaw and Jeager^ for the case where the velocity of the moving boundry is constant. The heat loss per unit area at such a boundry is: Q0.c. = P° / T(u,t) du (1 ) where u = z-vt (effective distance) Q0#c. = heat stored below the position of moving boundary per unit area the solution to above equation is: T(u,t) = AT/2 [ erfc (u+vt)/(2 Vat) + e ~vu/a erfc (u-vt)/2 V"cit) ] (2) and the integrated form would be: Q„ _ = (XAT/2v)[ 2v(t/a)°*5ierfc (v/2)(t/a)0*5 U • v • + 2 erf (v/2)(t/a)0'5] (3) The above equation has also been confirmed by Vogel.^3 With the vertical velocity of the oil/steam interface defined, the cumulative amount of heat stored in the steam zone per unit area of the interface between the steam and heated reservoir is: Qs#z. = VPctAT W The cumulative heat lost to and accumulated in the cap rock per unit area of steam zone/oil sand interface is: _ 00 - oo Qc#r. = Pc / T dz = pcAT / erfc zdz/2 95 Q0>r> = (2pc AT/V7 )( at)0-5 (5) where t is the elapsed time during which the unit area in question has been exposed to steam. The total heat usage is equal to the injected heat at any time prior to any heat production and is equal to: = ®o.c. + ^s.z. + ^c.r. (6) The following dimensionless variables are defined, tD = v2 t/4a (7) Qd - (v/4 XAT) dQ/dA = (v/4AAT) Q (8) and Ad = v pc ATA/q^ (9) they are then substituted in the heat equations (3, 4 and 5), therefore: °s.z. D = H (10) °c. r.D = (tD/^)0-5 (11) °o.c.D =((tD)°-5/2)ierfc(tD)0-5 + 1/4 erf (tD)0-5 (12) and ^TD = ^s.z.D + ^c.r.D + ^o.c.D (13) QTd = tp + (t p/TT)0 • ^ + (tp/4) 0 • 5 ierfc(tD)°*5 +1/4 erf (tD)0-5 (14) noting that Qt = / dQT/dA . dA (15) 0 -A Qt = (4XAT/v) I Qtd. dA (16) Jo the above equation can be rewritten , using the definition for the dimensionless area ,equation 9, and noting that Q-p 96 = q^t, as : A t — 4 /v^ I Qth o . D TD U"D 0 A, v2t/4 = I Qtd dAp J n 0 so: a I D fcD = I ^td dAD ^ b The above equation is solved by a step wise function of equal time increment, tp, and solving successively for each increment of area. For the first time step (time 0): AD0 = tD0/QTD1 for the second time step ( tD<|=2tpo)> tD< | = Qtd2AD0 + QTD1AD1 the only unknown in the above equation is A^. At this time the area that steam accumulates is the sum of the two area calculated or : ^AD^total = AD0 + AD1 the general equation for AD will be, N-2 ^AD^N-1 = 1/qTD1 ^ NtD0“^)^AD^i^QTD^i-1 ^ ^21 ^ i=l since, Av/5.615 = Barrels of oil per day and qi^fsAHl.v. = Barre- * - s steam per day combination of the above two equation and the definition of the dimensionless area, equation 9, will result in the 97 following equation: Ad = [(B.O.D)(pcAT)5.615/(B.S.D)(AHl-v#)fs] or, (B.O.D)/(B.S.D)= Oil/Steam Ratio = (ADfsAHlfVf)/(5.6l5 pcAT) (22) the above equation basically means that AD is a measure of the instantaneous oil steam ratio. Figure 41 illustrates Ad v s . dimensionless time for 1000 equal time step; each equal to 0.001. The cumulative curve in Figure 41 is ob tained by areal integration of the instantaneous curve. The above solution is the same trust as was suggested by Neuman 51 viz., the channeling of the steam which moves vertically downward. Newman added to the oil displaced from steam zone, the oil displaced by hot water. The contribution of the hot water is minimal for heavy oil reservoirs and may become significant as the reservoir oil gravity increases. He proposed the use of an overall oil/steam ratio which included the effectiveness of hot water, and the fraction of injected heat that is produced. Both of these assumptions require history matching. The new study presented here looks only at breakthrough conditions (no heat has been produced from the injected heat) and assumes no contribution from hot water to oil production (a valid assumption for heavy oil reservoirs). 98 5 0 . 0 DIMENSIONLESS TIM E Figure 41. DIMENSIONLESS RELATIONSHIP BETWEEN O IL/STEAM RATIO AND T IM E VO VO However, both methods by their nature show there is no effect of thickness on steam drive efficiency and that there is a linear effect of steam quality on the perform ance of steam drive. The following is an example for calculating the oil/steam ratio, using the above procedure, for run 9. The available data are: a = 0.875 ft2/day AHn , , = 2.82 x 105 -L • V • pc =25.9 BTU/ft3/°F AT = 345 °F fs= 68 * Oil in place = 7758 x<f>xhxAxS0 therefore for reservoir under study: oil in place (B/ft.) = 10880 also from the phyisical model data, the average oil produc tion rate, before the breakthrough, is 83 B/D. The velocity of the moving boundary (v) is calculated by dividing the average oil production rate (B/D) by the origional oil in place (B/ft.) hence, v = 0 . 0 0 8 1 ft./day. The dimensionless time (tD) is calculated by substituting the above information in equation 7. Therefore, tD=0.0077 and from Figure 38, Ap = 0.08. Substituting the above information in equation 22, oil/steam ratio = 0.3. The maximum oil steam ratio observed in the physical 100 model study is 0.20. The difference between the two can be attributed to the heat loses in the latteral direction that was not considered in the analytical model. It is worth emphasizing here that the preceding analy sis shows that the rate of heat injection required to maintain a constant downward advance of the steam boundary is constantly decreasing with time. Therefore, when break through was secured at some constant rate of steam injec tion, an increasing quantity of steam will be produced if the rate is maintained constant after breakthrough. In practice, the decline in the oil steam ratio is controlled to some extent by decreasing the steam injection rate after breakthrough. However, there must be a limit of how far the steam injection rate can be decreased. The downward velocity of the steam front has to be the result of hori zontal attribution of the oil column at the steam/oil interface. The attribution in turn results from a gas drive of the heated, mobile oil at that interface. Hence, if the steam injection rate is decreased further the steam velocity will be insufficient to drag the heated oil along the interface. The velocity of the moving boundary and therefore the production rate will decrease. Some steam will always be wasted in a steam drive operation because of the virtual impossibility of optimizing the heating and displacement processes by the injection of a single fluid. 101 The nature of the specific project and local economic factors will determine whether the engineer optimizes the process based on production rate or thermal efficiency. Actual field results as well as the model studies do indicate that the production rate in steam drive operation is indeed rather constant for a long time after break through. However, as for any engineering calculation of these very complex reservoir processes a precise correla tion of such ,fquasi-theoryn and operating results can not be expected. Many calculations, based on a wide spectrum of hypotheses, can be forced to fit the results of a reser voir process. The analysis presented herein does have the virtues of being consistent with most all the observations that have been made of steam drive operations: the override of the steam, the early breakthrough of steam, the absence of a marked effect of thickness, the effect of steam quali ty, the occurence of an optimum rate and the influence of the oil viscosity on the oil/steam ratio. 102 CHAPTER VII CONCLUSIONS This work was designed to investigate how the steam drive functions under certain conditions which have not yet been extensively encountered in practice: 1) The oil steam ratios that are to be expected when working in thin reser voirs, less than 27 feet in thickness, and 2) The oil steam ratios that are to be expected when the steam drive is applied in reservoirs containing high gravity oils, parti cularly at waterflood residual saturations. The results obtained with the scaled vacuum physical models are quite conclusive: 1. The oil/steam ratio is not significantly affected by reservoir thickness whenever the steam drive is sus tained by a steam channel between injection and production wells. 2. The oil/steam ratio, when sufficiently high injec tion rates can be attained, in reservoirs containing resi dual high gravity crude oils, will equate to a favorable energy balance. 3. Although not explored in detail, the results of the 103 experiments reveal the possibility that the steam drive may be competitive under certain conditions with waterflooding in exploiting reservoirs of high gravity crude oils, 4. The experiments have also confirmed earlier conclusions on the effect of the viscosity of the crude oil at steam temperature on the oil steam ratio. Although the oil/steam ratio is only a fractional power of the inverse of the viscosity of the crude oil, the effect is suffi ciently important so that the oil/steam ratio deteriorates as the viscosity increases. This result implies that attempts to exploit reservoirs of very viscous petroleum, bitumens and tar sands, may not be economically successful unless synergistic systems acting with the steam can be developed. The virtually trivial effect of reservoir thickness, say above 10 feet, that is predicted by these studies, has been verified to be true of actual field operations. A review of the results of such operations indicate that not only does the oil/steam ratio appear to be independent of thickness but that the oil steam ratios range between 0.16 and 0.28, with an average value of 0.22, much as would be predicted from the experiments described in this work. A quasi-theoretical analytical argument has been deve loped in this study which to a first approximation explains the reason why the oil/steam ratio is not dependent upon __________________________________________ 104J thickness when steam overriding dominates the steam drive process, When a reservoir is saturated with low viscosity fluids, either a high saturation of high gravity crude, or a high saturation of water following a waterflood, the injection of steam at high velocities results in an almost frontal displacement of the reservoir fluids. The resul ting ratios of produced reservoir fluid to steam injected are now much higher than if steam override or channeling occurrs. As a result, the oil steam ratios when the reservoir is filled with a high gravity fluid exceed 0.5 and may approach 1. When the reservoir contains only residual oil, following a waterflood, the experimental work indicates that the ratios may well be above 0.15, and therefore equate to a favorable energy balance, viz., the energy required to recover the oil is less than the energy content of the produced oil. The economics of using steam for recovering residual oil, and the competitiveness of steam drive with water- flooding high gravity crude oil reservoirs will ultimately depend on two factors: the unit cost of the fuel used for steam generation, and the well density required to attain the necessary high injection rates. Because the oil/steam ratio is a function of the viscosity of the crude at steam temperature, in order to 105 secure a favorable energy balance (oil/steam ratio) in reservoirs containing very viscous petroleum, it will be necessary to use higher average steam temperatures than have been used in the successful operations in the San Joaquin Valley and other basins in California and in the Lagunillas district in the State of Zulia in Venezuela. Because of the need of the higher temperature, the latent heat of a unit mass of injected steam will be less, the specific volume greater, and the thermal losses to the base and cap rocks will be higher. All these factors will result in poorer oil/steam ratios, and the overall econom ics of attempts to recover these very viscous petroleums may be jeapordized. The use of fuels that are valued less than the produced oil, and the development of techniques which economically supplement the use of steam will proba bly be required to permit exploitation of such accumula tions by the steam drive. The results of earlier experiments using scaled vacuum physical models of steam drive operations have shown re markable correlation with field results which suggests that the results of the experiments described in this work should also be in accord with field operations. However, because of the potential vulnerability of the scaling pro cedure to factors which cannot be scaled, viz., pore size distribution, capillary pressure, and residual oil satura 106 tions as they might be affected by the specific lithology of reservoir rocks and physico-chemical interaction of crude oil and reservoir brines, validation of these conclu sions must await the implementation of pilot and demonstra tion projects in the field. Some recommendations for further work follow from the conclusions which have been reached as a result of the current work. Studies should be extended to reservoirs which have a mechanical fracture, reservoirs which have multiple layers of different permeability and different degrees of vertical communication, and reservoirs into which are drilled horizontal bore holes for injection of steam. In addition, extended studies are recommended on the use of systems in which the steam drive itself is supplemented with non-condensible gases and the use of chemicals that may assist in the entrainment of the heated oil by the gas drive at the interface between the overriding steam and the oil column below. 107 NOMENCLATURE A Area of steam Zone, ft2 L2 c Heat capacity, BTU/lb. °F L2/t2T fs Steam quality, % p p g Acceleration of gravity, ft/sec4 1 L/t h Enthalpy, BTU/lb. L2/t2 AH-j^v^Latent heat of steam, BTU/lb. L2/t2 K Permeability, Darcy L2 Thermal conductivity, BTU/hr.ft.°F mL/t^T L Distance, ft. L Ly Latent heat of vaporization, BTU/lb. L2/t2 N Time step P Pressure, psi m/Lt2 q Volumetric Rate, cc/min. or Bbl/day L^/t q£ Heat injection Rate, BTU/day mL2/t^ Q Cumulative heat lost per unit area, BTU/ft2 ra/t2 S Saturation, dimensionless t Time, min., hr. or day t tp Dimensionless time AT Steam temperature less initial Reservoir temperature, °F T 108 V Velocity, ft/day L/t Greek Symbols a Thermal diffusivity, ft2/hr. L2/t Y Scaling factor, dimensionless X Thermal conductivity, BTU/ft.day,°F mL/Tt3 U Viscosity, cp m/Lt V Kinematic viscosity, cp m/Lt P Density, gr/cc or lb/ft^ m/L^ Ap po “ ps < i > Porosity, % a) With of the linear well model, inches L Subscripts a Aqueous phase for quality control cP Cap prototype c.r. Cap rock cM Cap model D Dimensionless M Model 0 OH o • o • Oil column p Prototype 109 Reservoir or residual Reservoir model Reservoir Prototype Steam Super heat Steam zone Total Total dimensionless Water Coordinates REFERENCES 1. Doscher, T. M.: Personal Communication, 1979. 2. Doscher, T. M.: ’ ’Scaled Physical Model Studies of the Steam Drive Process,” First Year Report to United States Department of Energy, Contract EY-76-5-03-0113 36 PA. 3. Huang, W. W,: ”Analysis of Steam Drive Process by Scaled Physical Models,” Ph.D Dissertation (June 1980), University of Southern California. 4. Doscher, T. M. and Haung, W. W.: ’ ’Steam Drive Perform ance Judged Quickly from use of Physical Models,” Oil and Gas J. (October 22, 1979) 52-57. 5. Marx, J. W. and Langenheim, R. H.: ’ ’Reservoir Heating by Hot Fluid Injection,” Trans. AIME, (1959) vol. 216, 312-315. 6. Myhill, N. A. and Stegemeier, G. L.: ” Steam-Drive Correlation and Prediction,” J. Pet. Tech. (February 1980) 173-182. 7. Gomaa, E. E.: ’ ’Correlation for Predicting Oil Recovery by Steamflood,” J. Pet. Tech. (February 1980) 331. 8. Farouq Ali, S. M. and Meldau, R. F.: ”Current Steam flood Technology,” J. Pet. Tech. (October 1979) 1332- 1342. 9. Wooten, R. W.: ’ ’Case History of a Successfull Steam- Flood Project - Loco Field,” SPE Paper 7548, (1978). 10. Hall, A. L. and Bowman, R. W.: ’ ’Operation and Perform ance of the Slocum Thermal Recovery Project,” J. Pet. Tech. (April 1973) 402-408. 11. Blevins, T. R., Aseltine, R. J. and Kirk, R. S.: ’ ’Analysis of a Steam Drive Project, Inglewood Field, California,” J. Pet. Tech. (September 1969) 1141-1150. Ill 12. Greaser, G. R. and Shore, R. A.: nSteamflood Perform ance in Kern River Field,1 1 SPE Paper 8834, Tulsa (April 1980). 13. Rhee, S.: "A Method for Predicting Oil Recovery by Steam Flooding Including the Effect of Distillation and Gravity Override,” Ph.D Dissertation (January 1979), University of Southern California. 14. Omoregie, 0. S.: ”Steam Drive-Definition and Enhance ment,” Ph.D Dissertation (June 1981), University of Southern California. 15. Willman, B. T., Valleroy, V. V., Runberg, G. W., Cornelius, A. J. and Powers, L. W.: "Laboratory Studies of Oil Recovery by Steam Injection,” J. Pet. Tech. (July 1961) 681-690. 16. Ozen, A. S. and Farouq Ali, S. M.: ”An Investigation of the Oil Recovery of the Bradford Crude by Steam Injection,” J. Pet. Tech. (June 1969) 692-698. 17. Myal F. R. and Farouq Ali, S. M.: "Recovery of Penn- Crude oils by Steam," J. Pet. Tech. (June 1970) 705- 710. 18. Myal, F. R.: "Steamflooding of Pennsylvania Crude Oils," M.S. Thesis (June 1968), the Pennsylvania State University. 19. Johnson, F. S., Walker, C. J, and Bayazeed, A. F.: "Oil Vaporization During Steamflooding," J. Pet. Tech. (June 1971) 731-742, 20. Volek, C. W. and Pryor, J. A.: "Steam Distillation Drive-Brea Field, California," J. Pet. Tech. (August 1972) 899-906. 21. Baker, P. E.: "An Experimental Study of Heat Flow in Steamflooding," Soc. Pet. Eng. J. (March 1969) 89-99. 22. Baker, P. E.: "Effect of Pressure and Rate on Steam Zone Developement in Steamflooding," Soc. Pet. Eng. J. (October 1973) 274-284. 23. Pujol, L. and Boberg, T. C.: "Scaling Accuracy in Laboratory Steamflooding Models," SPE Paper 4191, (1972). 112 24. Prats, M.: "Studies of Peace River Steam Drive Proc esses Using Scaled Physical Models," Canada-Venezuela Oil Sand Symposium, Edmonton, Canada (May 19YY)* 25. Loomis, A. G. and Crowell, D. C.: "Theory and Applica tion of Dimensional Inspectional Analysis to Model Study of Fluid Displacement in Petroleum Reservoirs," J. Pet. Tech. (August 1971) 1006-1014. 26. Niko, H. and Troost, P. J. P. M.: "Experimental Inves tigation of Steam Soaking in a Depletion-Type Reser voir," Bureau of Mines Report RI6546 (1964). 27. Harmsen, G. J.: "Oil Recovery by Hot-Water and Steam Injection," Proc. of English World Petrol. Cong. (1971), Applied Science Publishers, ltd., vol. 3, 243- 251. 28. Geerstma, J., Croes, G. A. and Schwarz, N.: "Theory of Dimensionally Scaled Model of Petroleum Reservoir," Trans. AIME, (1955) vol. 207, 118-123. 29. Nielson, R. L, and Tek, M. R,: "Evaluation of Scale-up Laws for two-phase Flow Through Porous Media," Soc. Pet. Eng. J. (June 1963) 164-176. 30. Rapoport, L. A.: "Scaling Laws for Use in Design and Operations of Water-Oil Flow Models," Trans. AIME, (1955), vol. 204, 143-150. 31. Perkins, F. M. Jr. and Collins, R. E.: "Scaling Laws for Laboratory Flow Models of Oil Reservoirs," Trans. AIME, (1960), vol. 219, 383. 32. Leverett, M.C., Lewis, W.B. and True, M. E.: "Dimen sional Model Studies of Oil Field Behavior," Trans. AIME, (1942), vol. 146, 175. 33. Croes, G. A. and Schwarz, N.: "Dimensionally Scaled Experiments and the Theories on the Water Drive Pro cess," Trans. AIME, (1955), vol. 204, 35-42. 34. Huygen, H. H. A.: "Laboratory Steamfloods in Half a Five-Spot," SPE Paper 6171, (1976). 35. Pursley, S. A.: "Experimental Studies of Thermal Re covery Processes," Presented at the Heavy Oil Symposium, Maracaibo, Venezuela (1974). 113 36. Erlich, R.: "Laboratory Investigation of Steam Dis placement in the Wabasca Grand Rapids A Sand," Canada- Venezuela Oil Sands Symposium, Edmonton, Canada (May 1977) 346. 37. Singhal, A. K.: "Physical Model Studies of Inverted Seven-spot Steamfloods in a Pool Containing a Lloydminster Type Heavy Oil," Petrol. Recovery Insti tute, Research Report RR-38 (November 1978). 38. Lo, H. Y.: "Laborasatory Model Study of Steamflood Oil Recovery," Petro. Recovery Institute, Research Report IR-5 (1977). 39. Stegemeier, G. L., Laumbach, D. D. and Volek, C. W.: "Representing Steam Process With Vacuum Models," SPE Paper 6787, Denver (1977). 40. Yortsos, Y. C.: "Analytical Modeling of Oil Recovery by Steam Injection," Ph.D Dissertation, Californiasa Institute of Technology (1979). 41. Grathoffner, E. H.: "The Role of Oil in Water Emulsion in Thermal Oil Recovery Processes," SPE Paper 7952 Ventura (April 1979). 42. Bursell, C. G. and Pittman, G. M.: "Performance of Steam Displacement in the Kern River Field," J. Pet. Tech. (August 1975) 997. 43. Mandl, B. and Volek, C. W.: "Heat and Mass Trasport in Steam Drive Process," Soc. Pet. Eng. J, (March 1969) 59. 44. Abrams, A.: "The Influence of Fluid Viscosity, Inter facial Tension, and Fluid Viscosity on Residual Oil Saturation," Soc, Pet. Eng. J. (October 1975) 437. 45. Taber, J. J.: "Dynamic and Static Forces Required to Remove aDiscontinuous Phase from Porous Media Con taining Both Oil and Water," Soc. Pet. Eng. J. (March 1969) 3. 46. Van Dijk, C.: "Steam Drive Project in the Schoonebeek Field, the Netherlands," J. Pet. Tech. (March 1968) 295-302. 47. Adelelotte, S. R, and Ramesh, A. B.: "Economic Feasi bility of Steam Drive in Light Oil Reservoirs," 5th 114 DOE Annual Symposium, Tulsa, (August 1979). 48. Hagoort, J., Leijnse, A. and Van Poolgeest, F.: "Steam Strip Drive: A Potential Tertiary Recovery," J. Pet. Tech. (December 1976) 1409-1419. 49. Van Lookern, J.: "Calculation Methods for linear Radial Steam Flow in Oil Reservoirs," SPE Paper 6788, (1977). 50. Dupuitt, J.: "Etudes Theoriques et Pratiques sur le Movement Due Eaux," Dumod, Paris 1863. 51. Neuman, C. H.: "A Mathematical Method of Steam Drive Process Application," SPE Paper 4757, Ventura (1975). 52. Carslaw, H.S. and Jaeger, J.C.: "Conduction of Heat in Solids," Oxford University Press, 2nd Ed., London (1959) 388. 53. Vogel, J. V.: Personal Communication, 1981.
Abstract (if available)
Abstract
The steam drive process has been extensively used in the recovery of moderately viscous crude oils in California, Venezuela and Canada. This study was conducted to scrutinize the application of the steam drive process for two other reservoir conditions which have not been considered attractive in the past. ❧ The earliest analytical studies of the steam drive process conceived of the steam drive to create a steam chest which frontally displaces the reservoir fluid. As a result of this assumed mechanism, a marked effect of reservoir thickness was predicted. However, the results of many field operations have revealed a surprising insensitivity of the oil/steam ratio (the energy balance of the process) to the reservoir thickness. This, together with the repeated observations in field operations that the steam overrides the oil column, has led to the hypothesis that the mechanism by which the steam drive works is different \ than that originally proposed. ❧ This study, as well as previously published studies with vacuum scaled physical models, show that the steam drive is a two-fold process. The overriding or channeling of the steam results in the heating of the oil at the interface between the oil column and the steam zone, and the heated oil is then displaced by a gas (steam) drive. It would follow from such a mechanism that thickness would have only a minor effect on the resulting oil/steam ratio. The scaled physical modeling described in this work has confirmed this hypothesis. ❧ The results obtained in this study confirm the results of an earlier study which showed the efficiency of the steam drive to be dependent on a fractional power of the reciprocal of the viscosity of the crude oil at steam temperature. It was therefore hypothesized that the oil/steam ratio would become very high if the steam drive was applied to a reservoir containing a high gravity, low viscosity crude. Contrary to earlier suggestions by other authors for the use of the steam drive for recovering high gravity crudes, this study shows that the efficiency of steam drive in such a process is not related to the volatility of the high gravity crude, but merely depends upon a high steam injection rate to efficiently displace the crude to a low residual saturation, while reducing the thermal losses from the reservoir. ❧ The scaled model studies reported here show that a high rate steam drive is extremely efficient in reservoirs containing low viscosity fluids. Favorable oil/steam ratios may be achieved in numerous water-flooded reservoirs containing residual saturations of high gravity crudes. ❧ This work has not explored the economic feasibility of implementing these novel uses for the steam drive
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Ghassemi, Farhad
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Steam drive: Its extension to thin oil sands and reservoirs containing residual saturation of high gravity crude
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