ent 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 al. (35) used a mixture of anaerobic thermophilic bacteria that fermented molasses in an MEOR field test to recover naphthenic crude. They also used raw sewage as an inoculum (100 L, along with 20 to 40,000 kg molasses) in later trials (1969-70). The deepest reservoir was 8,200 ft, where the pressure was 228 atm and the temperature was 97 °C. In most reservoirs tested (7 out of 10), the introduced microbial populations produced a positive effect on cumulative oil recovery.
Karaskiewicz conducted 18 field trials in Poland between 1961 and 1969 (36). Microbial cultures were obtained from soil and water samples taken in the vicinity of the oil fields and from sugar factory waters. The mixed culture includes the genera Arthrobacter, Clostridium, Mycobactetium, Peptococcus, and Pseudomonas grown in 10-L bottles with formation water plus 4% molasses, and incubated at 32 °C. The wells ranged in depth from 1,650 to 5,000 ft. The rate of additional oil recovery ranged from 20 to 200% of the original production rate. A second injection of nutrients was considered a major factor in the increased oil recovery.
Lazar (37) recently published an extensive review of MEOR work done in Romania during the last decade. Three areas of research are emphasized: (a) examination of the bacterial population in the formation water of the reservoir; (b) adaptation of these microorganisms in the laboratory for oil release; and (c) field testing of such adapted cultures. Seven wells were treated with microbial formulations and two conclusions were drawn: the bacterial population caused an increase of oil flow up to 200% for 1 to 5 years in 2 out of 7 reservoirs (the other five were unaffected), and much information about the ecology of the reservoir is needed before initiating any MEOR activity.
Overall, MEOR field trials in eastern Europe have been promising. Field testing in Romania is still in progress, and is supported in part by the Romanian government. There are obvious difficulties in obtaining key information regarding European MEOR fi