MEOR pilot sees encouraging results in Chinese oil field

Jan. 24, 2000
Microbial enhanced oil recovery (MEOR) tests in two wells indicated that the process could improve oil recovery from the Qinghai Seven Springs oil field in China (Fig. 1).
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Microbial enhanced oil recovery (MEOR) tests in two wells indicated that the process could improve oil recovery from the Qinghai Seven Springs oil field in China (Fig. 1).

Other EOR attempts had previously failed to increase production from the field that has relatively high-salinity formation water.

Well Zhong 19, in the Qinghai oil field, was one well in which a microbial treatment improved oil production (Fig. 2).
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The huff-and-puff pilot test involved two wells: Well Zhong 19 (Fig. 2) and Well 5-8. After the wells were shut in for 7 days, daily oil production from Well Zhong 19 increased from 2.5 to 4.1 tonnes/day (18-30 b/d). This elevated rate lasted for about 2 months.

The test included three bacteria strains isolated from Jianghan oil field produced-water samples. The three strains were bacillus sp. (DLA5), bacillus sp. (LB7), and pseudomonas sp. (HG9).

High-performance capillary electrophoresis, gas chromatography, and infrared spectroscopy analyzed the crude oils before and after microbial treatment. Results showed that the microbes degraded the long-chain alkanes and alkyl chains of aromatics, although the frameworks of aromatic ring cannot be changed. Microbial metabolization produced organic acids, acetones, ethers, and gases.

Based on the physical characteristics of oils before and after microbial treatment, the tests suggest that microbial treatment can reduce viscosity and wax content of crude oils.

Oil recovery in the laboratory test increased by 23.1%.

MEOR

Microbial enhanced oil recovery (MEOR) potentially can lower the cost of recovering oil in China.1-3 Some promising tests have been done.4-9

In 1990, the Daqing Petroleum Administrative Bureau was the first to use microorganisms for in situ fermentation to enhance oil recovery in the Daqing oil field.10 Since then, many other oil fields have conducted pilot tests in China, with satisfactory results.11 Most of them, however, used bacterial strains from ready-made packs sold by international companies.12

This article discusses the screening and evaluation of bacterial strains both in the laboratory and in a pilot test in Qinghai oil field. The field has a relatively low formation pressure and the formation-water salinity is about 20%. Physical characteristics of the crude are poor.

The wells in the field have low producing rates that continue to decrease, even though the field operators made many attempts to improve oil production by acidizing, fracturing, surfactant injection, thermal processes, microwave technology, etc., but without success.

The field has the following reservoir conditions:

  • Temperature-20-80° C.
  • Crude oil wax content-15-24.5%.
  • Formation water pH-6.0-9.0.
  • Permeability-greater than 75 md.

Laboratory experiments

The laboratory work involved bacteria DLA5, LB7, and HG9 that had been isolated from Jianghan oil field-produced water. The work planned to:

  • Degrade a heavy crude oil into a light oil and improve its mobility.
  • Generate organic acid and reduce the oil-water interfacial tension.
  • Generate gases by oxidation and degradation to enhance fluid mobility.

The laboratory evaluation of experimental bacteria determined the changes in the crude oil components before and after fermentation and the changes in the fermented fluid properties.

A Hewlett Packard Model 5890 chromatograph, equipped with a thermo-conductivity detector, compared the total amount of hydrocarbons and analyzed the changes in the saturated hydrocarbons before and after fermentation.

It also determined the crude oil biodegradation based on the changes in the ratio of pristane, C17/phytane, C18 (pristane, 2, 6, 10, 14-tetramethyl pentene; phytane, 2, 6, 10, 14- tetramethyl hexane).

In the test, the oven temperature was held at 100° C. for 2 min and then increased at a rate of 3° C./min to a final temperature of 300° C. for 30 min.13 The ratio of pristane, C17/phytane, C18 is taken as an index of the biodegradation of crude oil. A higher index indicates that more n-alkane is transformed into cycloalkanes, and therefore, crude-oil recovery improves.

Chromatography analyzed the percentage changes of saturated hydrocarbons, aromatic hydrocarbons, and asphaltenes in the crude oil before and after fermentation. The changes indicated the portion of the crude oil mainly affected by the bacteria.

A Bruker Model IFS infrared spectroscope determined the changes in the molecular composition of the crude oil and the physical characteristics before and after microbial fermentation.

An analysis of the gases, after microbial fermentation, determined the changes in the properties of the fermented fluid. The results showed that there were changes in the crude-oil viscosity and wax content. Also, a high-performance capillary electrophoresis determined the content of short-chain organic acid in the fermented fluid. The test also simulated the oil under atmospheric pressure.

MEOR simulation

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Table 1 shows the biological characteristics of the three microbes screened from Jianghan oil field-produced water.14-16

The MEOR simulation showed degradation of long-chain saturated hydrocarbons in the crude-generated lighter components. The chromatography of n-alkanes indicated that the curve not only is shorter with more iso-peaks, but also the peak values of C17 and C18 are much shorter than the peak values of pristane and phytane. The ratio of pristane, C17/phytane, C18 increase markedly.

The ratios of crude oil in Well Zhong 19 and Well 5-8 increased from 0.88 and 1.58 to 2.57 and 1.82 respectively. This verified that crude production improved with MEOR.

Oil compositions changed before and after the microbe treatment. The oil samples acquired saturated hydrocarbon, aromatic hydrocarbon, and asphaltene components.

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Table 2 shows the sample composition from each well. The results indicate that both saturated hydrocarbon and asphaltene contents in oil samples increased.

Well Zhong 19 had a larger increase in its saturated hydrocarbon content than Well 5-8. Also, aromatic hydrocarbon content decreased in both wells after the oil was treated with microbes. The changes can improve oil recovery.

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Infrared (IR) analysis of oil samples (Table 3) showed long-chain alkanes. Mixed bacteria strongly degraded the alkyl chains of aromatics in crude oils by generating organic acids, acetones, ethers, etc. during microbial fermentation. This process also indicates an improvement in the crude oil flow.

In the production of short chain organic acid, fermented liquid pH decreased significantly from 8.5 to 6.2, while the acid value of the crude oil increased. These pH changes reflect the production of organic acids by oxidation during bacterial fermentation.

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The short organic acid content and quantity of the fermented liquid (Table 4) indicated a maximum of 277.91 mg/l. These organic acids can decrease the interfacial tension of the fermented liquid.

A simulation model used the Lazar's scheme under normal pressure conditions. The simulation included three kinds of bacteria and field water mixed together with a few added nutrients. With conventional methods, saturated water and oil was displaced by water. When water cut reached 98%, displacement continued with water for more than 2 hr before being stopped.

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The next step injected into the model two pore volumes (PV) of fluid containing bacteria. The model was then placed in a box at a temperature of 50° C. for cultivation and observation (Table 5).

As shown in Table 5, mixed bacteria benefit MEOR. After 7 days, the incremental oil produced in Core L5 by mixed bacteria was 0.4 ml, which is equivalent to 10.5% of the original oil and 23.1% of the residual oil.

On the other hand, all the simulation models in the crude oil tests generated a large amount of gas within 72 hr. Large amounts of gas were produced before gas production ceased.

Chromatography analysis determined the quantity of gas produced from Well 5-8 oil after microbial treatment in the core. The produced gases mainly consisted of CO2 (2.82%) and N2 (61.3%). Oil was produced with the gas.

Qinghai field test

Laboratory results were the basis for the design of the microbial huff-and-puff MEOR test.17 The design included the following six points:

  1. Simulation experiments indicated that bacteria could degrade the crude oil in Wells 5-8 and Zhong 19.
  2. The test mode would be a microbial huff-and-puff.
  3. For convenience and result comparison, the working system remained constant before and after the test. No work was done in the wells. Pumps were left in the wells and injection was carried out through the casing.
  4. The bacterial fluid was prepared in the fermentation plant. The fluid for injection was then formulated at the well sites and injected with high-pressure piston pumps.
  5. After microbial injection, the wells were shut for at least 7 days to allow the microbes to ferment in situ.
  6. All facilities and pipelines were sterilized, and care was taken to ensure that all personnel were protected to prevent contaminating the field.

After the 7-day shut in, the wells showed a variation in the properties of oil and water. The numbers of live bacteria in the produced water had increased to 24 million/ml in Well Zhong 19 and 1.5 million/ml in Well 5-8.

The produced water contained all of the bacteria strains injected. The bacteria numbers in the water remained at a high level of 7,400/ml even after 2 months. This showed that the bacteria injected into the wells can survive and grow in the reservoir for a long time.

The produced water also showed an increase, by a factor of more than seven, in the amount of organic acid. Table 6 lists the physical characteristics of crude oil changes after the microbial treatment.

The microbial treatment decreased the viscosity and wax content of both oil samples. These changes help in displacing oil in the formation.

In Well Zhong 19, the water cut decreased by about 12.5%, and oil production increased from 2.5 tonnes/day (prior to the test) to 4.1 tonnes/day. The incremental oil production lasted for 2 months.

In Well 5-8, the measured oil production rate did not increase because of a pipeline leak. The water cut, however, decreased by about 10.05%.

The treatment also controlled paraffin depositions in both wells. The period of washing out the well increased from once a week before treatment to once every 55 days.

References

  1. Hitzman, D.O., "Microbial enhanced oil recovery-The time is now," 1990 International Conference on Microbial Enhancement of Oil Recovery, Microbial Enhanced Oil Recovery-Recent Advances, Donaldson, E.C., editor, Elsevier, 1991, pp. 11-20.
  2. Donaldson, E.C., Chilingarian, G.V., and Yen, T.F. Microbial Enhanced Oil Recovery, 1989.
  3. Burtch, F., "Introduction to the Fourth International MEOR Conference," Microbial Enhanced Oil Recovery-Recent Advances, Premuzic, E.T., and Woodhead, A., editors, Elsevier, 1993, pp. 1-6.
  4. Bubela, B., "Combined effects of temperature and other environmental stresses on Microbial Enhanced Oil Recovery," International Conference on Microbial Enhanced Oil Recovery, Donaldson, E.C., and Clark, J.B., editors, Afton, Okla., 1982.
  5. Lazar, I. "Microbial Enhancement of Oil Recovery in Romania," International Conference on Microbial Enhanced Oil Recovery, Donaldson, E.C., and Clark, J.B., editors, Afton, Okla., 1982.
  6. Lazar, I., "MEOR field trials carried out over the world during the last 35 years,". 1990 International Conference on Microbial Enhancement of Oil Recovery, Microbial Enhanced Oil Recovery-Recent Advances, Donaldson, E.C., editor, Elsevier, 1991, pp. 485-530.
  7. Lazar, I., "MEOR the suitable bacterial inoculum according to the kind of technology used," Results from Romania's last 20 year's experience, Paper No. SPE/DOE24207, 1992.
  8. Qin, T.L., and Yang, G.H.,"A brief introduction to the progress of MEOR in China, 1990 International Conference on Microbial Enhancement of Oil Recovery, Microbial Enhanced Oil Recovery-Recent Advances, Donaldson, E.C., editor, Elsevier, 1991, pp. 29-34.
  9. Zajic, E.J., "Scale up of microbes for single well injection." 1st International MEOR Workshop, King, J., and Stevens, D., editors, US DOE Bartlesville project office, 1987.
  10. Zhang, C.Y., and Zhang, J.C., "A pilot test of EOR by in-situ microorganisms fermentation in the Daqing oilfield." Microbial Enhanced Oil Recovery-Recent Advances, Premuzic, E.T., and Woodhead, A., editors, Elsevier, 1993. pp. 231-44.
  11. Xiu-Yuan, W., and Wang, X.J., "Advances in Research, Production and Application of Biopolymers used for EOR in China," 1990 International Conference on Microbial Enhancement of Oil Recovery, Microbial Enhanced Oil Recovery-Recent Advances, Donaldson, E.C., editor, Elsevier, 1991, pp. 467-82.
  12. Wang, B., and Dong, L., "Paraffin characteristics of waxy crude oils in China and the methods of paraffin removal and inhibition." Paper No. SPE29954, 1995.
  13. Gevertz, D., Paterek, J.R., et al., "Isolation and characterization of anaerobic halophilic bacteria from oil reservoir brines," 1990 International Conference on Microbial Enhancement of Oil Recovery, Microbial Enhanced Oil Recovery-Recent Advances, Donaldson, E.C., editor, Elsevier, 1991, pp. 45-60,
  14. Balkwill, D.L., "Number, diversity and morphological characteristics of aerobic, chemoheterotrophic bacteria in deep subsurface sediments from a site in South Carolina," Geomicrobiology, Vol. 7, No. 1-2, 1989, pp. 33-52.
  15. Brock, T.D., and Madigan, M.T., Biology of Microorganisms, Fifth Edition. Prentice Hall, Englewood Cliffs, N.Y., 1988.
  16. Bhupathirju, V. K., et al., "Isolation and characteristics of novel halophilic anaerobic bacteria from oil field brines," 1990 International Conference on Microbial Enhancement of Oil Recovery, Microbial Enhanced Oil Recovery-Recent Advances, Donaldson, E.C., editor, Elsevier, 1991, pp. 131-44,
  17. Yen, T.F., Microbial Enhanced Oil Recovery: Principle and Practice, CRC Press, Boca Raton, Fla, 1990.

The Authors

Zhengguo He is doing research on MEOR at the Jianghai Petroleum University. He holds a BS in microbiology and an MS in biotechnology from the Huazhong Agriculture University.

Yuehui She is an associate professor at Jianghai Petroleum University. He holds a BS from Beijing Petroleum University.

Tingsheng Xiang is a senior engineering in the geochemistry research center of Jianghai Petroleum University.

Feng Xue is a lecturer on instrumental analysis at Jianghai Petroleum University. He holds a BE and ME from Peking University.

Bowen Mei is a professor in Geochemistry. He holds a BS and MS from Peking University.

Yong Li is director of the Institute of Drilling & Production Technology. He holds a BE in petroleum engineering.

Bangqing Ju works on enhanced oil recovery. He has a BE in petroleum engineering.

Hai Mei is a PhD candidate in environmental engineering at University of Southern California, Los Angeles.

Teh Fu Yen is a professor at the University of Southern California, Los Angeles, specializing in MEOR.