Study On Cooperation Between Microorganisms And CO₂ Flooding In Low Permeability Reservoir To Improve Oil Recovery

Although CO₂ flooding and microbial flooding have been carried out in some pilot experiments of oilfields,the research on their synergistic effect is relatively few.This paper takes the Jingbian carbon dioxide region of Yanchang oilfield as the research object,comprehensively evaluates the oil displacement potential of exogenous and endogenous microorganisms cooperating with CO₂ respectively and aims to provide a theoretical basis for exploration on the synergistic effect between microorganism and CO₂.The main results of this paper are as follows:?1?Using high-throughput sequencing technology,the diversity of endogenous microbial community structure in different blocks of Yanchang oilfield is studied in this paper.Different blocks differ greatly in the phylum classification level.There are 44,45,46 bacterial colonies in Xingzi Chuan water flooding samples;46,48,48 colonies in Gangu Yi air flooding samples;20,25 colonies in Jingbian CO₂ flooding samples.In terms of the species richness of the samples,each block has met the data requirements for the experiment.?2?Three high-efficiency hydrocarbon reduction bacteria are screened from the Yanchang oil-water samples,and the degradation rate of three bacteria C3,W1 and KB is respectively 56.5%,42.2%,44.4%.Analyzing the crude oil after the action of three bacteria by four components and GC-MS,the bitumen of crude oil is found to be degraded to a certain extent,and the crude oil shows a lightweight trend.?3?The endogenous microbial activator in Jingbian CO₂ flooding oilfield is developed and their activation effect is evaluated.The activator formula was obtained by screening optimization:Molasses 7.5 g/L,Na NO₃ 5 g/L,K₂HPO₄ 3.5 g/L.Activating them in the atmosphere of air,N₂ and CO₂ respectively,it turns out that activator in CO₂ atmosphere produces more small molecule organic acids and methane gases than under air and N₂,indicating that the activation of endogenous microorganisms in CO₂atmosphere is more favorable to improve the recovery rate.By using the vanish dilution method to evaluate the activation effect of endogenous microorganisms,sulfate reducing bacteria were better inhibited in reservoir,nitrate reduction bacteria were not well activated.From this we can infer that CO₂ displacement solution is not suitable for the survival of nitrate reduction bacteria,probably because it belongs to carbonized water.?4?Under the reservoir temperature and pressure,the synergistic effect between microorganism and CO₂ is explored by using physical simulation of oil displacement experiment.In 50m D core displacement,the oil recovery rate of CO₂ flooding was60.41%;CO₂ compound exogenous microbial flooding was 63.46%,CO₂ compound endogenous microbial flooding was 66.3%.It indicates that microorganisms can improve the oil recovery rate on the basis of CO₂ flooding.