To seek an effective oil recovery approach, Brevibacillus brevis and Bacillus cereus were screened and applied in a Microbial Enhanced Oil Recovery (MEOR) process to recover oil from Daqing low permeability areas. The selected bacteria were found to be highly compatible with indigenous microbes; the laboratory data shows:
The oil-water interfacial tensions (IFT) after microbial treatment decreased by 50%;
The alkanes with middle and high carbon numbers could be degraded;
The viscosity of treated crude oil decreased by about 40%;
The content of paraffin and resin decreased from 1.3% to 4.9%, and from 0.7% to 2.6%, respectively, thus improving significantly the rheology of the crude oil; and
The oil recovery from laboratory coreflooding achieved about 6.5% original oil in place (OOIP) over that achieved by waterflooding.
From 2002 to 2005, microbial huff 'n' puff trials have been conducted in 70 wells altogether in the Daqing Chaoyanggou (0.5×10-3µm2-25×10-3µm2) and Pubei areas (103×10-3µm2). Effectiveness was observed in 43 out of 60 Chaoyanggou wells, with accumulative incremental oil amounting to 9175.7 tons. Eight out of 10 Pubei wells showed effective results as well, with 1873 tons of accumulative incremental oil. The total incremental oil from the two areas amounted to 11,000 tons, with an average of about 158 tons for one individual well.
Based on the success of microbial huff 'n' puff trials, a microbial flooding pilot test with two injectors and 10 producers was carried out in the Chaoyanggou low permeability area (25×10-3µm2) in June 2004. The bacteria injection was followed by a pressure decrease in two injectors and an increase in the fluid injection. The daily produced fluid and oil increased from 43.6 tons to a high of 79.6 tons and from 24.7 to 40.8 tons, respectively. Water cut decreased from 45.2% to 38.6%. By the end of Dec, 2007, 7 out of 10 wells showed significant oil production response. The incremental oil is about 13,000 tons. The analysis made to the effective and non-effective wells demonstrates that MEOR plays an important role in establishing an effective driving system.
There are six oil layers in the Daqing periphery oilfields. The main reservoirs are the fluvial facies and delta depositions, which are buried from 500 to 2200 meters deep. Daqing periphery oilfields have the unfavorable features of low permeability (from 0.1 × 10-3 µ m2 to 200 × 10-3 µ m2), low reserves, and low output. The ground oil viscosity is from 8 mPa•s to 100 mPa•s with a wax content from 20% to 30%. Due to these adverse conditions, both recoverable reserves and waterflood efficiency in these areas are low. A driving system cannot be established and oil production has decreased dramatically (Hou, 2005; Ren et al., 2005; Zhang et al., 2004). A new, economical, and effective way to further enhance oil recovery is urgently needed.
In 1926 Beckman first presented the concept of MEOR. Currently, it has been applied successfully in EOR, with promise of a successful future (Cheng et al., 2006; Dietrich et al., 1996; Feng and Chen, 1999; Feng et al., 2005; Gao et al., 1999; Jiang et al., 2005; Li et al., 2002; LV et al., 2002; Portwood, 1995; Streeb and Brown,1992; Wang and Liu, 2005; Wang et al., 2002; Wang et al., 2004; Xing et al., 2000; Yang et al., 2005; Zhang et al., 2001).