Use of Indigenous or Injected Microorganisms for Enhanced Oil Recovery

Transcription

1 Use of Indigenous or Injected Microorganisms for Enhanced Oil Recovery Michael J McInerney, Roy M Knapp, John L Chisholm, Vishvesh K Bhupathiraju, John D Coates University of Oklahoma, Norman, Oklahoma, 73019, USA ABSTRACT Microbially enhanced oil recovery may offer an economic alternate to enhance oil recovery One of the major factors that limits oil production is permeability variation in the reservoir Because of permeability variation, the recovery fluid, usually water, preferentially flows through high permeability regions, leaving the oil present in less permeable regions unrecovered In laboratory experiments, we showed that the stimulation of in situ microbial growth by nutrient injection results in substantial permeability reductions in sandstone cores, that microbial growth and consequently permeability reduction preferentially occur in high permeability regions, and that the plugging of high permeability regions diverts fluid flow into less permeable regions A field test of the microbial plugging process was conducted in the Southeast Vassar Vertz sandstone reservoir located in Payne County, OK Selective reductions in the interwell permeability between the injection well and three production wells were observed after stimulation of the growth of indigenous microorganisms by nutrient injection Also, a major water channel from the injection well to another portion of the reservoir was partially plugged Increases in alkalinity and sulfide concentration in the produced brines confirmed that metabolic activity occurred as a consequence of nutrient injection A causal relationship between nutrient injection and sulfide production was observed, which supported the conclusion that the reservoir had a microbial community capable of mineralizing molasses with sulfate as the terminal electron acceptor These results show that a microbial plugging process for enhanced oil recovery is technically feasible Introduction Continued industrialization and economic growth will increase the demand for oil, especially to meet the growing demand for liquid transportation fuel The demand for crude oil often exceeds existing production in many industrialized nations, thereby increasing the reliance of these countries on foreign imports This slows economic growth, reduces employment and aggravates trade deficits Conventional oil production technologies are able to recover only about one-third of the oil originally in place in a reservoir In the United States, it is estimated that over 300 billion barrels of oil remain unrecovered after conventional technologies reach their economic limit [3] New technologies to recovery this residual oil offer the most timely and cost effective solution to reverse the decline in domestic oil production and to increase the oil reserves of the United States Microbial Biosystems: New Frontiers Proceedings of the 8 th International Symposium on Microbial Ecology Bell CR, Brylinsky M, Johnson-Green P (ed) Atlantic Canada Society for Microbial Ecology, Halifax, Canada, 1999

2 Microbially enhanced oil recovery (MEOR) has several unique advantages that make it an economically attractive method to enhance oil recovery MEOR processes do not consume large amounts of energy as do thermal recovery processes and MEOR processes do not depend on the price of crude oil as do many chemical recovery processes Because microbial growth occurs at exponential rates, it should be possible to produce large amounts of useful products quickly from inexpensive and renewable resources Economic analysis of two recent MEOR field trial show that in addition oil is produced for as little as three dollars per barrel [2, 7] MEOR Technologies MEOR processes can be grouped into three main categories depending on the type of production problem and where the process occurs in the reservoir [5] Well bore clean out processes involve the use of hydrocarbon-degrading or scale-removing bacteria to remove deposits from tubing, rods, and other surfaces in the well Wells treated with hydrocarbondegrading bacteria do not require as frequent chemical treatments to maintain oil production, which greatly reduces operating costs and extends the lifetime of the well [15] This approach is a mature commercial technology with thousands of wells treated on a regular basis [11,12] While there is much controversy about the proposed mechanism for improved oil recovery and whether this technology is as effective as claimed, it has survived in the market place for many years The next MEOR technology is well stimulation where an oil well close to its economic limit is treated with a mixture of anaerobic bacteria and a fermentable carbohydrate, usually molasses [4] The production of acids, solvents, and gases in the well bore region is believed to alter the wettability of the rock and improve the drainage of oil into the well Although the technology is easy to implement, the stimulation of oil recovery is very inconsistent and this technology does not seem to be effective in sandstone reservoirs [4] Microbially enhanced waterflooding processes are done late in the course of a waterflood and involve the injection of nutrients and or microorganisms into the reservoir in order to stimulate microbial activity throughout the reservoir In carbonate formations, the production of organic acids by the microbial fermentation of carbohydrates is believed to alter pore structure due to the dissolution of the carbonate minerals and substantial improvements in oil production in carbonaceous sandstone reservoirs have been reported with this process [7,18] In sandstone formations, substantial increases in oil production require that the interfacial tension between the oil and water phases be reduced by a factor of 10,000 or more in order to release the oil that is entrapped in small pores by capillary pressure The lipopeptide biosurfactant produced by Bacillus licheniformis strain JF-2 substantially reduces the interfacial tension between oil and water [8,9] The introduction of this organism along with other anaerobic bacteria in two field trials in Oklahoma has increased oil production and decreased the water to oil ratio of the produced fluids [2] The addition of nitrate and/or inhibitors of sulfate reduction to injection waters are also used to control hydrogen sulfide production and improve oil recovery [16,17] In addition to the above approaches, we have developed a microbial plugging process to reduce permeability variation in oil reservoirs in order to improve the performance of waterfloods [10] Variations in permeability are common-place in petroleum reservoirs and dramatically affect the ultimate recovery of oil Water preferentially flows through the most

3 permeable layers of the rock with little or no movement in the less permeable regions The oil present in the low permeable regions is by-passed and unrecovered The stimulation of the in situ growth of indigenous microorganisms in the high permeability regions by nutrient injection reduces water movement in these regions and diverts fluid flow into the less permeable regions of the reservoir that have high oil saturations Laboratory experiments have showed that in situ microbial growth substantially reduces the permeability of sandstone cores, that microbial growth occurs preferentially in the high permeability regions, and that plugging of the high permeability regions diverts fluid flow into less permeable regions [13,14] Since the process does not require the production of a specific chemical or the growth of a specific organism, it should be applicable in many reservoirs Methods A field trial of the microbial plugging process was conducted in the Southeast Vassar Vertz sandstone reservoir (Figure 1), which is a hypersaline oil reservoir [1,6] Well 7-2 was the injection well for the trial and wells 5-1, 5-2 and 7-1 were the production wells Approximately 56 metric tons of cattle feed molasses and 19 metric tons of ammonium nitrate were injected into the reservoir over a three month period [6] Tracer studies and pressure interference tests were conducted before and after nutrient injection to determine if the fluid flow patterns changed as a result of microbial growth and activity [6] It should be noted that the purpose of the field pilot was to determine if flow patterns changed and not whether significant amounts of oil were recovered The reservoir had been extensively waterflooded and an analysis of the oil production history indicated that oil recovery in the portion of the reservoir where the trial was to be conducted was close to the theoretically predicted maximum for secondary oil recovery processes [6] Thus, little oil remained to be recovered by improving sweep efficiency Results and Discussion Two tracer studies conducted prior to nutrient treatments showed that a major flow path existed between the injection well, 7-2, and the production wells in the 1A tract, with breakthrough times of 16 and 18 days After the nutrient treatments, two peaks of tracer were observed in the wells of the 1A tract The first peak occurred about 20 days after tracer injection and the second peak occurred between 55 and 70 days after tracer injection, depending on the well location This shows that a portion of the fluid injected into well 7-2 took an alternate path to the wells in the 1A tract, indicating that the water channel that existed between well 7-2 and the wells in the 1A tract had been partially blocked [6] Initial pressure interference tests showed that interwell permeability variations existed between the injection well 7-2, and wells 5-1, 5-2, and 7-2 (Table 1) For all three wells in the test area, the time of first arrival of the pressure pulse and the rate of pressure change increased after nutrient treatment, indicating that the interwell permeabilities in the pilot area were altered as a result of microbial activity Very close agreement was obtained between the permeability reduction factors calculated from the time of first arrival of the pressure pulse compared to those calculated from the rate of pressure change (Table 1) [6], indicating that the assumptions used in the respective approaches were valid The largest change in interwell permeabilities occurred between wells 7-2 and wells 5-1 and 5-2, which were also the regions that had the highest initial permeabilities Thus after microbial treatment, the

4 Figure 1 Plat map of the Southeast Vassar Vertz sand unit 11 R 1 W Tract 1 Tract 2 Unit Boundary 14 Tract Tract Tract 1A T 18 N Tract 4 Tract Tract 6 6 Tract 7 4 Tract 8 Active production well Active injection well Inactive injection well = 1320 ft Fig 1 Map showing the location of wells at the Southeast Vassar Vertz sand unit interwell permeabilities were more uniform than prior to nutrient treatment These are the desired results of a selective plugging process for enhanced oil recovery Increases in alkalinity and sulfide concentration in the produced brines confirmed that metabolic activity occurred as a consequence of nutrient injection [6] No organic acids or alcohols were detected in the produced brines indicating that a microbial community exists in the reservoir capable of the mineralization of carbohydrate to carbon dioxide Consistent with this hypothesis, Bhupathiraju et al [1] found that the produced brines contained high levels of heterotrophic haloanaerobes, halophilic sulfate reducing bacteria and halophilic methanogenic bacteria A causal relationship between nutrient injection and sulfide production was observed [6], which supports the conclusion that the reservoir had a

5 microbial community capable of mineralizing molasses with sulfate as the terminal electron acceptor Table 1 Well Relation to Nutrient Treatment Pulse Size (Barrels per day) Rate of Pressure Change a Permeability (millidarcies) Percent Permeability Reduction (from pressure pulse) Time of Pressure Pulse Arrival (h) 5-1 Before Percent Permeability Reduction (from arrival time) After Before After Before Acknowledgements We thank W Jenkins, B T Hopkins, R A Raiders, P K Sharma, T T Liu, B E Jackson, M Coughlin, and D W Wareck for technical assistance and R S Tanner for helpful discussions and comments References 1 Bhupathiraju VK, McInerney MJ, Knapp RM (1993) Pretest studies for a microbially enhanced oil recovery field pilot in a hypersaline oil reservoir Geomicrobiol J 11: Bryant RS, Stepp AK, Bertus KM, Burchfield TE, Dennis M (1993) Microbial enhanced waterflooding field pilots Devel Petrol Sci 39: Fisher WL, Tyler N, Ruthven CL, Burchfield TE, Pautz JF (1992) An assessment of the oil resource base of the United States Oil Resources Panel, U S Department of Energy, Bartlesville Project Office, DOE/BC-93/1/SP, Bartlesville, OK 4 Hitzman DO (1983) Petroleum microbiology and the history of its role in enhanced oil recovery In: Proceedings of the International Conference on Microbial Enhancement of Oil Recovery (E C Donaldson and J B Clark, eds) pp Technology Transfer Branch, U S Department of Energy, Bartlesville, OK 5 Jenneman GE (1998) Identification, characterization and application of sulfide-oxidizing bacteria in oilfields Microbial Ecol in press 6 Knapp RM, Chisholm JL, McInerney MJ (1990) Microbially enhanced oil recovery In: Proceedings of the SPE/UH emerging technologies conference, pp Institute for improved ol recovery, University of Houston, Houston, Texas 7 Knapp RM, McInerney MJ, Coates JD, Menzie DE, Bhupathiraju VK (1992) Design and implementation of a microbially enhanced oil recovery field pilot, Payne Count,

6 Oklahoma SPE Presented at the 1992 Annual Technical Conference and Exhibition, Dallas, TX 8 Lazar I, Dobrota S, Stefanescu MC, Sandulescu L, Paduraru R, Stefanescu M (1993) MEOR, recent field trials in Romania: reservoir selection, type of inoculum, protocol for well treatment and line monitoring Devel Petrol Sci 39: Lin S-C, Minton MA, Sharma MM, Georgiou G (1994) Structural and immunological characterization of a biosurfactant produced by Bacillus licheniformis JF-2 Appl Environ Microbiol 60: McInerney M J, Javaheri M, Nagle DP Jr (1990) Properties of the biosurfactant produced by Bacillus licheniformis strain JF-2 J Indust Microbiol 5: McInerney MJ, Jenneman GE, Knapp RM, Menzie DE (1985) In situ microbial plugging process for subterrranean formations U S Patent No 4,558, Nelson L, Schneider DR (1993) Six years of paraffin control and enhanced oil recovery with the microbial product, Para-Bac TM Devel Petrol Sci 39: Portwood JT (1995) A commercial microbial enhanced oil recovery process: statistical evaluation of a multi-project database, In: The Fifth International Conference on Microbial Enhanced Oil Recovery and Related Biotechnology for Solving Environmental Problems (R S Bryant and K L Sublette eds), pp Office of Scientific and Technical Information, CONF Raiders RA, McInerney MJ, Revus DE, Torbati HM, Knapp RM, Jenneman GE (1986) Selectivity and depth of microbial plugging in Berea sandstone cores J Indust Microbiol 1: Raiders RA, Knapp RM, McInerney MJ (1989) Microbial selective plugging and enhanced oil recovery J Indust Microbiol 4: Streeb LP, Brown FG (1992) MEOR-Altamount/Bluebell field project PE Presented at the SPE Rocky Mountain Regional Meeting, Casper, Wyoming 17 Telang AJ, Ebert S, Foght JM, Westlake DWS, Jenneman GE, Gevertz D, Voordouw G (1997) Effect of nitrate injection on the microbial community in an oil field as monitored by reverse genome probing Appl Environ Microbiol 63z: Wagner, M, D Lungerhausen, H Murtada, and G Rosenthal 1995 Development and application of a new biotechnology of molasses in-situ method: detailed evaluation for selected wells in the Romashkino carbonate reservoir In: The Fifth International Conference on Microbial Enhanced Oil Recovery and Related Biotechnology for Solving Environmental Problems (R S Bryant and K L Sublette eds), pp Office of Scientific and Technical Information, CONF