Study Of The Mechanism Of Synergistic Oil Displacement Between Hydrophilic Emulsifying Functional Bacteriaand Endogenous Bacteria

Crude oil is a valuable non-renewable resource.With the development of exploration technology and large-scale exploitation in China,the production of conventional light oil has gradually declined,whereas unconventional resources,such as heavy oil,play an important role in the energy supply.China has abundant reserves of heavy oil.However,thermal recovery,chemical methods,and other traditional recovery technologies cannot exploit heavy oil effectively on a large scale because of their high energy consumption and cost.Microbially enhanced oil recovery has economic,environmental,and wide spread applications.Metabolites,such as biosurfactants,bioemulsifiers,biogas,and organic acids,produced by microorganisms can reduce crude oil viscosity and improve oil recovery.Therefore,microbial methods are becoming a key technique for improving the recovery of heavy oil.In this study,the degradation performance of Geobacillus sp.K4,the community structure of indigenous microbes,hydrocarbon degradation,and viscosity changes of heavy oil under different activation methods were investigated.Finally,the microbial interaction relationships and oil displacement performance under the synergistic effect of Geobacillus sp.K4 with indigenous bacteria are also discussed.This study provides theoretical support for the application of synergistic oil displacement using indigenous and exogenous bacteria.The physiological and biochemical characteristics and emulsification performance of Geobacillus sp.K4 was investigated at formation temperature,and experiments on oil degradation by K4 under different culture conditions were performed.The distributions of saturated hydrocarbons,aromatic hydrocarbons,resin,and heteroatoms in the crude oil before and after degradation were analyzed.The p H,surface tension,and bacterial concentration of the culture medium were determined before and after degradation.Functional genes related to alkane and aromatic degradation were identified by sequencing the whole genome.Strain K4 can grow in the environment of 65℃,pH 6-8,salinity 5000 mg L^-1-20000 mg L^-1,and has good emulsification performance on toluene,m-xylene,and diesel oil.Whole-genome sequencing analysis showed that many functional genes,such as alkane hydroxylase,hydrolase,and catechol 2,3-dioxygenase genes,were annotated in the genome of strain K4.Crude oil degradation experiments showed that the degradation rate of alkanes by strain K4 exceeded 60%and had a certain degradation effect on organic heterocyclic compounds.After degradation,the content of N₁O₁and O₂compounds increased.Low and high organic nutrient activators were selected,and the structural changes in the endogenous flora in the reservoir and their effects on crude oil were studied using different addition methods.The oil viscosity decreased to 707.72 mPa·s and530.04 mPa·s after adding low organic nutrient activator and high organic nutrient activator,respectively.The lowest oil viscosity 494.58 mPa·s was achieved after adding the above two activators alternately.Thus,alternating the addition of the two activators is beneficial for reducing the viscosity of crude oil.The results of GC-MS and FT-ICR MS analyses showed that the addition of high organic nutrients promoted the degradation of long-chain n-alkanes and increased the content of N₁O₂and O₂compounds.Microbial structure analysis showed that the phylum Synergistetes,including Anaerobaculum.Metabolomic analysis showed that the alternating addition of nutrients was conducive to the degradation of heterocyclic compounds and aromatic compounds in heavy oil,thereby reducing the viscosity of crude oil.Under the alternating addition of low/high organic nutrient activators,strain K4was used as an exogenous bacterium for co-cultivation with the indigenous microbial community.Changes in the microbial community structure,production of volatile fatty acids and biogas,and the composition of crude oil were analyzed.The results showed a synergistic effect between Geobacillus sp.K4 with indigenous bacteria reduced the content of volatile fatty acids,such as acetic acid and propionic acid,and the content of CH₄in the biogas increased.The oil viscosity decreased to 504.8 mPa·s after the stimulation of indigenous bacteria,while the oil viscosity decreased to 384 mPa·s after the synergistic action of strain K4 and indigenous bacteria.GC-MS analysis showed that the addition of strain K4 enhanced the degradation of n-alkanes with high carbon numbers.FT-ICR MS analysis showed that the degradation of organic heterocyclic compounds was enhanced.Metagenomic analysis showed that Methanothermobacter,a hydrogenotrophic methanogen,was activated after the addition of indigenous bacteria to the indigenous microbial community,as well as Pseudothermotoga,Thermoanaerobe,and other functional bacteria.The metabolic pathways for alkanes,aromatic hydrocarbons,and fatty acids were identified.Therefore,the synergistic effect of strain K4 and the indigenous bacteria was beneficial for the viscosity reduction and methanation of heavy oil.