An Experimental Investigation of Performance Evaluations for Seawater and CO 2 Injection Using Dual Core Methodology at Reservoir Conditions

Transcription

1 An Experimental Investigation of Performance Evaluations for Seawater and Injection Using Dual Core Methodology at Reservoir Conditions Authors: Xianmin Zhou, Fawaz M. Al-Otaibi, AlMohannad A. Al-Hashboul and Dr. Sunil L. Kokal ABSTRACT In this study, a novel methodology of dual coreflooding testing was first developed and described in detail, and then applied to evaluate the displacement efficiency and performance of seawater and supercritical carbon dioxide ( ) injection in tests of two carbonate core plugs with different permeabilities at reservoir conditions. The dual coreflooding apparatus, which consists of seven components, can be used for the individual or simultaneous injection of one- or twophase fluids into core plugs of various length arranged in a single or dual coreflooding configuration. The orientation of the single or dual core holder with its test core plugs can be changed horizontally or vertically for different experiments. The experimental conditions of this new apparatus go up to 150 C for temperature, up to 6,000 psi for pore pressure and up to 10,000 psi for confining pressure. As an example of the application of this dual coreflooding experiment setup, a test of the different oil recovery schemes of seawater flooding as a secondary enhanced oil recovery (EOR) process followed by a injection, and as a tertiary EOR process was conducted at reservoir conditions. The results from the dual coreflooding experiments are discussed here for high and low permeability carbonate rocks, as is the potential of EOR projects. The experimental procedures followed in these dual core experiments are provided and have the potential to become a gold standard for other such studies. INTRODUCTION Development of coreflooding apparatuses started in the 1940s. Various types of this equipment are used in laboratory experiments for reservoir engineering processes. Experimental techniques were also devised, such as the classical steady-state method, examples including the Penn State method 1, the Hassler method 2, the single core dynamic method (Hafford s) 3 and the stationary fluid method 4. With further development of laboratory testing techniques, the apparatus started to accommodate the use of in situ saturation imaging techniques by X-ray to measure saturations when two or three fluids are injected into the core. Depending on research objectives, the components of the coreflooding apparatus were changed to meet the requirements of the investigation. The basic coreflooding apparatus has been used in many research areas, such as tests of oil recovery by seawater and low salinity waterflooding 5, by chemical flooding 6 and by carbon dioxide ( ) injection 7. A review of the coreflooding apparatuses employed in these areas found that a single core holder was always used no matter which research objectives were investigated. In this article, a dual coreflooding apparatus is proposed. It is designed to test the performance of different oil recovery schemes of seawater flooding involving supercritical carbon dioxide ( ) injection at reservoir conditions. The objective is an evaluation of the practicability of a dual coreflooding system. DUAL COREFLOODING APPARATUS A dual coreflooding apparatus has been custom designed to perform tests on stacked or composite core plug samples to study oil recovery by improved oil recovery (IOR) and enhanced oil recovery (EOR) processes. It has the capacity to evaluate the impact of reservoir heterogeneities, such as permeability contrast and gravity override, on the performance of oil-water production at reservoir conditions. Figure 1 is a schematic of the coreflooding apparatus. The core holders are placed horizontally with a high permeability core plug (HPCP) core holder arranged above a low permeability core plug (LPCP) core holder. A detailed description of the dual coreflooding system can be found in Zhou et al. (2015) 8. APPLICATION OF THE DUAL COREFLOODING APPARATUS As an example of the application of the dual coreflooding experiment setup, a test of the different oil recovery schemes of seawater flooding as a secondary EOR process along with injection, and as a tertiary EOR process was conducted for carbonate core plugs with different permeabilities at reservoir conditions. Properties of Fluids Brines. Two types of brines were used in this study: field FALL 2016 SAUDI ARAMCO JOURNAL OF TECHNOLOGY

2 T = 102⁰C MV#31 MV#29 MV#30 P = 3200 psi MV0 MV#19 High Permeability Core Plug MV#25 MV#35 MV#43 AV0 MV#18 MV#20 MV#27 MV#26 P = 4500 psi MV#36 AV3 MV#17 MV#40 MV#42 MV#39 MV#41 MV#47 AV4 AV5 AV6 MV#45 MV#14 MV#15 MV#16 MV#11 MV#12 MV#13 MV#22 MV#24 P = 3200 psi MV#46 Live Oil Foam Connate Water Sea Water Dead Oil MV#21 MV#32 Low Permeability Core Plug MV#28 MV#34 MV#37 MV#23 MV#38 MV#33 MV#44 N 2 MV#48 MV#8 MV#9 MV#10 MV#5 MV#6 MV#7 MV#4 MV#3 MV#2 MV#1 Pump 2 (Confining Pump) Pump 1 Pump 3 MV#49 Fig. 1. A schematic of the dual coreflooding apparatus. connate water and seawater. The field connate water was used to saturate the core plugs for brine permeability measurement and to acquire the initial water saturation (S wi ). Seawater was used to displace live oil in the core plugs for purposes of evaluating its displacement efficiency. This was done by injecting seawater simultaneously into both the HPCP and the LPCP. The composition, density and viscosity of both brines are described in a previous paper 8. Dead and live crude oils. A dead crude oil from a carbonate reservoir was used in this study to set up the S wi and to age the core plugs at reservoir conditions. Separator crude oil and gas were collected from the same reservoir and recombined for the live crude oil sample. The live oil was then used to age the core plugs and to represent the oil phase for the seawater flood and miscible flooding experiments. The viscosity and density of the dead and live crude oils at reservoir temperature are described in a previous paper 8.. was also used as a displacing agent for tertiary oil recovery at a pressure of 3,200 psi and temperature of 102 C. This created a miscible flooding condition with the live crude oil similar to that in the reservoir. The minimum miscible pressure difference between the live oil and was 2,600 psi. The viscosity and density of the are described in a previous paper 8. Preparation of Core Plugs Core plugs. The core plugs were selected from a carbonate reservoir and scanned to ensure that no fractures or permeability barriers were present. Table 1 shows the length (L) and diameter (D) of the two core plugs. Composite ID Composite 1 (HPCP) Composite 2 (LPCP) L (cm) D (cm) PV (cc) K b (md) S wi (%) S oi (%) K eo at S wi (md) Table 1. Initial data for live oil flooding at reservoir conditions SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2016

3 Setting up of S wi and original oil in core (OOIC) saturation, S oi. Before running the dead crude oil flooding for purposes of setting up the initial conditions, S wi and S oi, several tests were done to saturate the core plugs with field connate water and measure the brine permeabilities. Core plugs were assembled in a stack using Teflon tape, aluminum foil and one layer of Teflon shrink tube. The aluminum foil functioned as the diffusion barrier found between core and overburden sleeve. The procedure of setting up the initial conditions in detail can be found in Zhou et al. (2015) 8. Table 1 shows the results of the tests. Aging of composite core plugs with live crude oil. After the initial water and OOIC saturations were set up, live oil flooding was conducted at reservoir conditions a pore pressure of 3,200 psi, confining pressure of 4,500 psi and temperature of 102 C for both the HPCP and the LPCP. Every day for three weeks, one pore volume (PV) of live oil was injected into each composite core at a flow rate of 1.0 cc/min to check the stabilization of the injection pressure and the effective oil permeability of the core plugs. The S wi and S oi were, respectively, 24.6% and 75.4% for the HPCP and 17.6% and 82.4% for the LPCP. Oil Recovery by Seawater and Injection Oil recovery by initial miscible flooding. After the initial seawater flooding and after the remaining oil saturation had been established, the inlet and outlet valves of both composites were closed. All the lines, which were filled with seawater, were displaced with. Then the two composites were opened again, and was injected simultaneously into both at a rate of 0.2 cc/min. The recovered oil was collected from the two composites separately. Differential pressures and injection pressures for each composite were also recorded as a function of time. Injection of a diverting system. To investigate the effect of permeability contact and to mitigate its impact on oil recovery, a diverting system was injected into the HPCP composite. The main idea was to block the HPCP composite so that the subsequent would travel through the LPCP composite and recover the bypassed oil. The diverting system used for this experiment is described in a previous paper 9. Second miscible flooding. After the diverting system injection, both the HPCP and the LPCP composites were opened for the second miscible flooding at an injection rate of 0.2 cc/min. Oil production and differential pressure across the composites and injection pressure were recorded individually for the HPCP and the LPCP. Oil recovery by seawater flooding. Once both composites were aged with live oil at reservoir conditions, seawater was injected simultaneously into both the HPCP and the LPCP at injection rates of 0.5 cc/min, 1.0 cc/min and 2.0 cc/min, until the water cut reached 99%. The recovered oil was collected from the two composites separately as a function of PVs of injected seawater. The differential pressures across both composites and the injection pressure were also recorded as a function of time. RESULTS AND DISCUSSION Profile of Differential Pressure during Seawater and Injection Figure 2a shows the differential pressure across the HPCPs and the LPCPs vs. total PV of seawater injection. At the breakthrough point of the injection fluid, the differential pressure across the HPCP core reached a maximum value of 0.8 Fig. 2. Comparison of differential pressure vs. the sum of PV injected during simultaneous injection for the HPCP and LPCP composites: (a) seawater injection, and (b) injection. FALL 2016 SAUDI ARAMCO JOURNAL OF TECHNOLOGY

4 Cumulative Oil Recovery Oil Recovery % (OOIC) % (OOIC) Seawater Flooding 0.5 cc/min HPCP LPCP 1.0 cc/min 2.0 cc/min 1 st Flood Total PV Injected by Seawater (Initial and 2 nd ) Total PV Injected by Seawater (Initial and 2 nd ) Flooding at 0.2 cc/min 19% 2 nd Flood Fig. 3. Overall oil recovery by seawater, initial and second flooding after diverting the system with a slug injection at reservoir conditions. psi and then dropped to a value of about 0.2 psi at an injection rate of 0.5 cc/min. For the LPCP, the differential pressure across the core reached a maximum value of 11 psi and then dropped down to the same value as the HPCP. This phenomenon is due to the seawater bypassing through the HPCP and the effect of rock heterogeneity. Figure 2b presents the differential pressure drop across both cores during initial injection. For the LPCP composite, the performance of the initial injection was quite different from that of the seawater injection. After breakthrough, the differential pressure drop across the two cores was different a second peak value of differential pressure was observed for the LPCP at a value greater than 5 psi. This was due to a two-phase and three-phase flow in the LPCP. Slow continuous oil production was observed beyond 0.2 PVs of the injected. Oil Recovery during Seawater and Injection Figure 3 shows the overall oil recovery with seawater and before and after the diverting system slug injection. The results show exceptional recovery 98% in the HPCP composite after the seawater and the first injection cycles. Due to seawater and bypassing the HPCP, the performance of the LPCP composite was relatively poor. By plugging the HPCP with the diverting system slug, the subsequent was able to extract some of the remaining oil from the LPCP composite. CONCLUSIONS Based on results and observations of seawater and flooding using a dual coreflooding apparatus at reservoir conditions, the following conclusions can be drawn: 1. A novel apparatus and experimental procedure for dual coreflooding experiments was applied successfully to study oil recovery by seawater and as well as conformance control using a diverting system at reservoir conditions. 2. Novel methodologies of dual coreflooding tests are an effective technique, and a dual coreflooding apparatus is a very useful tool with which to study oil recovery and performance by IOR and EOR processes, and to evaluate the effect of permeability contrast, reservoir heterogeneities and injection flow rate on oil recovery at reservoir conditions. ACKNOWLEDGMENTS The authors would like to thank Saudi Aramco management for the permission to publish this article. Special thanks Amin M. Alabdulwahab and Sentbilmurugan Balasubramanian for the preparation of a diverting system. This article was presented at the International Symposium of the Society of Core Analysts, Snow Mass, Colorado, August 21-26, SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2016

5 REFERENCES 1. Morse, R.A., Terwilliger, P.L. and Yuster, S.T.: Relative Permeability Measurements on Small Core Samples, Oil and Gas Journal, August 1947, pp Hassler, G.L.: Method and Apparatus for Permeability Measurements, U.S. patent No. 2,345,935, April Richardson, J.G., Kerver, J.K., Hafford, J.A. and Osoba, J.S.: Laboratory Determination of Relative Permeability, Journal of Petroleum Technology, Vol. 4, No. 8, August 1952, pp Leas, W.J., Jenks, J.H. and Russell, C.D.: Relative Permeability to Gas, Journal of Petroleum Technology, Vol. 2, No. 3, March 1950, pp Yousef, A.A., Al-Saleh, S.H., Al-Kaabi, A. and Al-Jawfi, M.S.: Laboratory Investigation of the Impact of Injection Water Salinity and Ionic Content on Oil Recovery from Carbonate Reservoirs, SPE Reservoir Evaluation and Engineering, Vol. 14, No. 5, October 2011, pp Shedid, S.A.: Experimental Investigation of Alkaline/ Surfactant/Polymer (ASP) Flooding in Low Permeability Heterogeneous Carbonate Reservoirs, SPE paper , presented at the SPE North Africa Technical Conference and Exhibition, Cairo, Egypt, September 14-16, Kokal, S.L., Al-Otaibi, F.M. and Zhou, X.: Laboratory Evaluation of Performance of WAG Process for Carbonate Rocks at Reservoir Conditions, SPE paper , presented at the SPE Kuwait Oil and Gas Show and Conference, Kuwait City, Kuwait, October 8-10, Zhou, X., Al-Otaibi, F.M., Kokal, S.L., Al-Hashboul, A.A., Balasubramanian, S. and Al-Ghamdi, F.A.: Novel Insights into IOR/EOR by Seawater and Supercritical Miscible Flooding Using Dual Carbonate Cores at Reservoir Conditions, paper presented at the 18 th European Symposium on Improved Oil Recovery, Dresden, Germany, April 14-16, AlOtaibi, F.M., Zhou, X., Kokal, S.L., Senthilmurugan, B., Al-Hashboul, A.A. and Al-Abdulwahab, A.M.: A Novel Technique for Enhanced Oil Recovery: In-Situ Emulsion Generation, SPE paper , presented at the SPE Asia Pacific Enhanced Oil Recovery Conference, Kuala Lumpur, Malaysia, August 11-13, BIOGRAPHIES Xianmin Zhou is a Petroleum Engineer with 40 years of experience working in Saudi Aramco s Exploration and Petroleum Engineering Center Advanced Research Center (EXPEC ARC). His focus areas are at present in paleo oil and heavy oil recovery studies. Prior to joining Saudi Aramco in 2010, Xianmin worked as a Senior Petroleum Engineer/Senior Special Core Analyst for four major oil companies: Daqing Petroleum Research Center, China; Core Lab Inc., U.S.; Omni Labs Inc., U.S.; and Intertek/ Westport Technology Center, U.S. His areas of expertise include special core analysis; and chemical enhanced oil recovery studies; reservoir characterization that includes developing methods for measuring two-phase and three-phase relative permeability; single and dual coreflooding apparatuses at reservoir conditions; and wettability studies. Xianmin has authored or coauthored 30 papers on the above subjects in Chinese and Canadian journals, and in several Society of Petroleum Engineers (SPE) journals. He has published four patents. In 1976, Xianmin received his B.S. degree in Petroleum Engineering from Daqing Petroleum Institute, Heilongjiang, China, and in 1996, he received his M.S. degree in Chemical and Petroleum Engineering from the University of Wyoming, Laramie, WY. Fawaz M. Al-Otaibi is a Petroleum Engineer at Saudi Aramco s Reservoir Characterization Department. Prior to that, he worked as a Supervisor of the Petrophysics Unit in the Exploration and Petroleum Engineering Center Advanced Research Center (EXPEC ARC). Fawaz has worked in many technical positions and a variety of disciplines, including production engineering and reservoir management, within Saudi Aramco. He has led research projects on both enhanced oil recovery using carbon dioxide ( EOR) and reservoir fluids. Fawaz has evaluated different EOR methods, such as water-alternating gas (WAG) and tapered WAG during EOR flooding. He has also taught courses on EOR and coreflooding theories and applications. Currently, Fawaz is leading a group of scientists and technicians to conduct studies to investigate several techniques in overcoming the gravity override during EOR. He is an active member of the Society of Petroleum Engineers (SPE) and has published numerous SPE papers and technical journals. Fawaz also has five filed patents. He is a Certified Petroleum Engineer and has received several awards and other recognitions from SPE. In December 1997, Fawaz received his B.S. degree in Chemical Engineering from King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia. FALL 2016 SAUDI ARAMCO JOURNAL OF TECHNOLOGY

6 AlMohannad A. Al-Hashboul is a Petroleum Engineer with Saudi Aramco s Reservoir Engineering Technology Team at the Exploration and Petroleum Engineering Center Advanced Research Center (EXPEC ARC). Since joining Saudi Aramco in July 2014, he has been involved in enhanced oil recovery (EOR) research projects, specifically EOR. He is a member of the Society of Petroleum Engineers (SPE). In 2014, AlMohannad received his B.S. degree in Petroleum Engineering along with a minor in both Mechanical Engineering and Mathematics from Texas Tech University, Lubbock, TX. Dr. Sunil L. Kokal is a Senior Petroleum Engineering Consultant and a Focus Area Champion of enhanced oil recovery (EOR) in the Reservoir Engineering Technology Team of Saudi Aramco s Exploration and Petroleum Engineering Center Advanced Research Center (EXPEC ARC). Since he joined Saudi Aramco in April 1993, he has been involved in applied research projects on EOR/improved oil recovery (IOR), reservoir fluids, hydrocarbon phase behavior and production-related challenges. Currently, Sunil is leading a group of scientists, engineers and technicians to develop a program for EOR and to conduct studies and field demonstration projects. The main driver for his research is to increase the ultimate oil recovery to 70% and so add billions of barrels of reserves. Sunil has written over 100 technical papers and has authored the chapters Crude Oil Emulsions and Reservoir Fluid Sampling for the revised edition of the SPE Petroleum Engineering Handbook (2006). He has been the associate editor for the Journal of Petroleum Science and Engineering, the SPE Reservoir Evaluation and Engineering Journal and the Journal of Canadian Petroleum Technology. He has been a keynote speaker, helped organize several petroleum engineering-related conferences and symposia, and taught courses on EOR, reservoir fluid properties and other related topics. A Registered Professional Engineer, Sunil is a member of the Society of Petroleum Engineers (SPE) and the Association of Professional Engineers, Geologists and Geophysicists of Alberta (Canada). He received the prestigious 2012 SPE DeGolyer Distinguished Service Medal, the 2011 SPE Distinguished Service Award, the 2010 SPE Regional Technical Award for Reservoir Description and Dynamics, and the 2008 SPE Distinguished Member Award for his services to the society. Sunil also served as a SPE Distinguished Lecturer during He has received several other awards, including best paper awards from the Canadian Petroleum Society, an outstanding technical editor award, and several internal company awards for publications, service, teamwork and technical contributions. Sunil has mentored several young professionals both at Saudi Aramco and for the SPE. In 1982, he received his B.S. degree in Chemical Engineering from the Indian Institute of Technology, New Delhi, India, and in 1987, he received his Ph.D. degree in Chemical Engineering from the University of Calgary, Calgary, Alberta, Canada. SAUDI ARAMCO JOURNAL OF TECHNOLOGY FALL 2016