Research On Characteristic Microbial Diversity Of Shale In Fuling

The immature,organic-rich shales represent a worldwide source of unconventional gas.Methane production by microorganisms in situ is the main biogenic methane origin.It is necessary to study the metabolic pathway and microbial flora characteristics of methane production in shale environment for shale gas exploitation and enhanced oil recovery.This study collected Fuling shale sample as the research object and reveals the characteristic microflora of the target shale reservoir through the combination of traditional microbiology and modern molecular ecology methods.The research results are as follows:Based on molecular ecology method,the total microbial DNA of original shale samples was extracted16S rDNA was sequenced and bioinformatics analyzed.The bacteria in the original shale sample are mainly:The genera Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium,Acinetobacter,Halomonas,and Methylobacterium were identified.There are Pseudomonas and Thermus in individual shale samples.The main archaea are Nitrososphaeraceae,Methanobacterium and Candidatus＿Nitrocosmicus in original shale.Based on the traditional microbiology and molecular ecology methods,different substrates（betaine,sodium acetate and CO₂/H₂）and native shale characteristic microorganisms were cultivated,and the microflora characterization was carried out in each reaction period,during which the main metabolites CH₄ and CO₂ content was tested.The highest CH₄ content in shale 1,shale 2 and shale water was 0.23mg/L,0.10and 0.60,and the highest CO₂content was 1070.64,64.99 and 20.42mg/L,respectively.Based on the contents of three kinds of CH₄ and CO₂,shale 1 was selected for enrichment culture of three different metabolic substrates to further reveal the mechanism of methane production shale in Fuling.The shale cultivated the substrate by betaine has the highest CH₄content of 0.58mg/L,and the highest CO₂ content of 1636.14mg/L,which is about 2.5 times and 1.5times higher than the highest CH₄（0.23mg/L）and CO₂（1070.64mg/L）contents in the original shale,respectively.The CH₄ content of the shale metabolized by sodium acetate and CO₂/H₂ hardly changed compared with that of the shale without substrates.However,the content of CO₂（137.4mg/L）in the shale metabolized by sodium acetate was significantly reduced.The bacterial communities in which betaine was the substrate were Bacillus,Desemzia,Oceanobacillus and Paraliobacillus.The main archaea communities were Candidatus＿Nitrososphaera,Nitrososphaeraceae,Candidatus-Methanomethylicus,Candidatus＿Nitrosotenuis,and Nitrososphaeraceae.Analyses of CH₄ and CO₂ content and metabolites showed that the addition of betaine substrate could increase the production of CH₄,which proved that the shale reservoir had the potential to enhance oil recovery by microorganisms.