Effect Of Bioconversion On Pore Structure And Permeability Of Coal Rock

The low permeability,low porosity and high stress of coal seams in China are not conducive to the production of coal bed methane.In recent years,some scholars have proposed coalbed methane microbial enhanced mining technology.The pores of coal are used as groundwater and coalbed methane storage sites and migration channels,and their structural characteristics will directly affect the enrichment and migration of coalbed methane.However,the existing research on bio-enhanced coal bed methane technology is more focused on low-rank coal such as lignite and biogas production,and there are relatively few studies on the pore structure changes after bio-enhanced coal,especially medium and high rank coal.The mechanism of coal bioconversion is still to be further studied,and there are few direct experimental studies on bioconversion to change the permeability of coal seam.Therefore,studying the effect of bioconversion on bituminous coal pore microstructure and its permeability is of great significance for improving coal seam structure and increasing reservoir permeability.This article adopts the method of joint research between laboratory experiments and theoretical analysis to study the microstructure and surface chemical properties of bituminous coal by bioconversion,the paper reveals the mechanism of bioconversion and studies the effect of bioconversion on pore permeability.The main research conclusions are as follows:(1)By carrying out the modification experiment of biological nutrient solution,the effect of bioconversion on the pore microstructure of bituminous coal was studied.High pressure mercury intrusion(MIP),low temperature nitrogen adsorption(LP-N₂GA)and scanning electron microscopy(SEM)techniques were used to characterize the pore size distribution,pore connectivity and surface morphology of coal samples.According to the pore structure characteristics,the most suitable p H and nutrient solution treatment methods of bioconversion were determined.The results showed that bioconversion increased the distribution of macropores,reduced micro-and mesopores,and increased the porosity of Tashan and Pingdingshan coal samples by 33.80%and 22.89%,respectively.The optimal p H of the nutrient solution used by the microorganisms to change the pore structure is 7.Mine water contains more biological nutrients,and the nutrient solution is more conducive to microbial activity and has a greater impact on pore structure.(2)The mineral content,crystal structure and surface groups of coal before and after bioconversion were characterized by X-ray diffraction(XRD)and Fourier infrared spectroscopy(FTIR)techniques,revealing the mechanism of bioconversion.Due to bioconversion,some microorganisms enter the coal pores.Through a series of biological actions,the organic matter on the coal surface is consumed by the microorganisms,reducing the oxygen-containing functional groups,degrading the coal surface,reducing the quartz content,increasing the pyrite content,and reducing the degree of coal crystallization.Due to the degradation of organic matter,the pore size gradually expands,and these changes lead to enhanced pore connectivity.(3)Through the test of permeability and porosity of biocoversion,the effect of bioconversion on permeability properties was studied.The results show that under two different biological nutrient solutions,bioconversion increased the permeability of Tashan coal samples by 496.78%and 651.12%,respectively.And the nutrient solution rich in trace elements such as Ni,Co,Se,W is more conducive to the change of pore permeability properties.After bioconversion,the stress sensitivity decreases,but the permeability sensitivity to porosity increases,and the change of pore microstructure leads to the increase of coal sample permeability.