 formation water of less than 10 x 104 ppm salt content, preferably a carbonate reservoir, and a temperature of approximately 38 °C.
Petrogen, Inc. did some preliminary field testing with 24 wells during 1977-82. Wells varied in depth from 300 to 4,600 ft. Some 75% of the wells showed a pressure increase of 10 to 200 psi. The type of microbial or nutrient injectant was not defined. Four wells doubled production for 6 months, and 12 increased production by 50% for 3 months. The production increase was indicated to average 42%; however, the final results remain to be reported (26).
The first MEOR project in the Rocky Mountains was initiated in 1983 (27). An independent oil operator purchased three field service operations from Petroleum Bio-Resources Company. These were (a) a reservoir field conditioning system to avoid plugging; (b) use of a microorganism that produces gas and surfactant; and (c) use of a microorganism that produces a polysaccharide for mobility control. The most recent information regarding this field project indicated that production immediately doubled, which was attributed to well stimulation, whereas the remainder of the wells in the field increased from 26 to 60 bbl/day, which was considered due to mobilization of oil by microorganisms and waterflooding (28).
Microbial flooding is being tested for oil recovery in an oil field near Nowata, Oklahoma, by NIPER, the U.S. Department of Energy, and two industrial paticipants (29). A microbially enhanced waterflood is being implemented in a field that has been waterflooded for more than 35 years and in a lease where the average oil production per well is currently 0.4 bbl/day. This microbial waterflood test is a carefully monitored field experiment, and should provide much needed documentation and information for future MEOR testing. Laboratory compatibility testing and coreflooding studies were done to optimize microbial formulations for this test (30, 31, 32).
Bryant and Douglas (30) have demonstrated the oil recovery efficiency of several different bacterial strains in Berea
sandstone cores. Treatment with microorganisms could recover an average of 32% more residual light crude oil than waterflood recovery. There were some spore-forming bacteria that brought about a recovery of 60 and 50% more crude oil. Heavy oil (API 14 and 17) Berea sandstone core experiments showed that selected microbial strains could recover up to 72% of the heavy oil left after waterflooding.
The United States has not been as active in field tests of microorganisms for EOR as some of the eastern European countries.
Kuznetsov (3) reported that in 1950 bacteria were present in certain oil-gas-bearing strata in the Saratov and Guguruslan areas of the USSR in such numbers that large quantities of CO2 were generated (depth was approximately 3,300 ft). Apparently methane was also formed. In subsequent work, Kuznetsov et al. injected mixed aerobic and anaerobic bacteria together with acid-hydrolyzed substances from peat and soils, shut in the well for 6 months, and then put the well in production (26). The rate of oil production rose from 275 to 300 bbl/day; however, 4 months later it had fallen to 270 bbl/day. No other work has been reported concerning these field tests.
Von Heningen et al. (34) reported on two field tests performed in the Netherlands. The year and location of the tests are unknown. In one test they used Betacoccus dextranicus in a sucrose-molasses medium of 10% total sugar content and obtained a 30% increase in cumulative oil recovery. The second test used a mixed culture of slime-forming bacteria in 50% molasses. The oil-to-water production ratio changed to 1:20 compared to 1:50 before treatment.
Field tests in Czechoslovakia in the mid 1950s by Dostalek and Spurney (34) utilized injected sulfate-reducing (Desulfovibrio) and hydrocarbon-utilizing (Pseudomonas) bacteria with nutrients (generally molasses). The daily average oil production increased by nearly 7% during the 6-month experiment period. No further work has been reported since 1958.
In Hungary, Jaranyi et a