Laboratory Study On Activating Indigenous Microorganisms At S12 Block In Shengli Oilfield To Enhance Oil Recovery

Based on the analysis of community structure of indigenous microorganisms at S12 block in Shengli Oilfield, a formula of selective-activating agent was screened out and the feasibility of activating indigenous microorganisms at S12 block to enhance oil recovery was studied through physical simulation experiments. The main research contents were listed as follows:1. Analysis of community structure of indigenous microorganisms at S12 block in Shengli OilfieldWith selected media, the community structure of indigenous microorganisms in six water samples (including recycled produced water for flooding reservoir at S12 block in Shengli Oilfield and produced waters from five oil wells of the reservoir) was analyzed. The results proved the bio-diversity of microorganisms at S12 block, including both the beneficial bacteria (hydrocarbon degrading, denitrifying, and methane-producing bacteria) and the detrimental bacteria (iron, sulfur, sulfate reducing, and total growth bacteria). It supports the possibility that the oil recovery at S12 block can be enhanced by injecting proper nutrients, selectively activating the beneficial stratal microorganisms and inhibiting the detrimental ones in the reservoir formations.2. Screening of activation agent to stimulate the stratal microflora selectively at S12 block in Shengli OilfieldBased on the theory of bio-inversion of oil in reservoir by Ivanov, the activation agent ST-12Y, which was mainly made up of corn syrup, was screened out by considering the population of living bacteria, surface-tension reducing efficiency, emulsification efficiency and the economical budget. It could effectively activate the beneficial bacteria and restrain the detrimental bacteria with desirable results. The hydrocarbon degrading bacteria increased from 1-10 to 105-106 cell/ml, theABSTRACTdenitrifying bacteria increased from below 10 to 103-104 cell/ml, and the methane-producing bacteria increased from below 10 to 10-102 cell/ml. After the activation of the indigenous microorganisms, an increase of saturated short-chain hydrocarbons and a decrease of saturated long-chain hydrocarbons content in the crude oil occurred. Thus the enhancement of hydrocarbon emulsification and the fluidity were observed obviously. The change of acetate concentration reflected the succession from aerobic to anaerobic microorganisms in the culture.3. Physical simulation study on indigenous microbial floodingIn order to determine the oil recovery efficiency from waterflooded residual oil, the change of system pressure, the concentration of acetate, the yield and the composition of biogas, the indigenous microbial flooding process in stratum was simulated through laboratory experiments with the crude oil and connate water from S12 block. The results showed that the oil recovery from residual oil had been increased by 4.7% after 36 days culture by adopting air-assistant technique (liquid/air 1:10 v:v). Based on the synergistic effect of the ecosystem of reservoir, 8.3% of the in-situ residual oil after waterflooding was recovered after two treatments of 77 days, mainly depending on the anaerobic microorganisms. The results strongly support the theory of the bio-inversion of oil in reservoir. The concentration of methane in the biogas increased with incubation time and the maximum concentration could reach 74.45%. The H2S was not checked out throughout the experiment, which showed that the yield of H2S had been effectively restrained.The results of this thesis will hopefully provide the theoretical basis and technologic support for the design of enhanced oil recovery project by activating indigenous microorganisms. And it has been put into use in-situ at S`I2 block.