Pilot Test of Indigenous Microorganism Flooding in a Heavy Oil Reservoir

Indigenous microbial flooding technology injects nutrients (sometimes mixed with air), activates the useful indigenous microbes which multiply and metabolize rapidly, and oil recovery enhanced. The technology was carried out through in Dagang oilfield in China from 2001 and mostly used in high temperature oilfield. Generally, the technology injects only basic nitrogen source mixed with air and utilizes residual oil in the reservoir as carbon source. Whereas, exgenous microbial flooding tests carried out in the past mostly inject carbon source, nitrogen source and no air.

Based on the research of reservoir geology, the analyses of development situation and study of nutrients, the pilot test was conducted in a low temperature(20°C) heavy oil(80mPa• S) reservoir in a trial block with 4 injection wells and 7 production wells. The test is different from the past MEOR tests in injecting molasses as carbon source, nitrogen source and air at the same time. It injected 0.05 pore volume and lasted for 2 years.

Field performance monitoring and product ion tracking results show: ① the indigenous bacteria were activated with the number increased 2-3 orders compared with pre-test, and microbial population structure changed apparently; ②properties of formation water were changed, the content of HCO3- in formation water varied greatly, and emulsion was found; ③Although CO₂ can be generated when molasses is decomposed and activity of producing methane was strengthened, the content of CO₂ and CH₄ in the gas of oil well changed slightly; ④oil produc increased in wells, and total oil increase was 5, 626t up to Jun., 2013. ⑤That the crude oil is emulsified by microbes is the primary mechanism of Indigenous Microbial Flooding Technology and that biogas generated by microbes is not the primary mechanism were determined.

Indigenous Microbial Flooding Technology injecting organic carbon source, nitrogen source and air simultaneously was appiled successfully in a low temperature heavy oil reservoir, which would serve as an example for similar reservoirs in high water cut stage.