热解作用下不同煤岩类型孔隙结构差异演变模式OA

Deep coalbed methane(CBM)is of important strategic significance to energy security and low-carbon development.However,the differential pore development patterns of different coal lithotypes throughout the complete thermal evolution path have not been figured out,which restricts the occurrence mechanism study and reservoir evaluation of deep CBM.Taking the low-maturity coal of the Haerwusu Mine in the Junggar Coalfield of the Ordos Basin as the simulation sample,this paper analyzes the differential variation characteristics and controlling factors of coal pore structures at different evolutionary stages by means of field emission scanning electron microscopy(FESEM),high-pressure mercury intrusion porosimetry(MIP),low-temperature nitrogen(N2)adsorption,and low-temperature carbon-dioxide(CO2)adsorption,and other characterization techniques.Based on this,a pore structure evolution model is established.The following results are obtained.First,the coal pore volume exhibits a bimodal distribution of micropores and macropores,with mesopores having the smallest pore volume,and micropores being the main contributors to specific surface area.With increasing thermal evolution degree,the volume and specific surface area of micropores generally show a trend of first decreasing and then increasing,those of mesopores display a sharp decrease followed by basic stability,and those of macropores exhibit a phased variation of first increasing and then decreasing.Second,different macroscopic coal lithotypes show significant difference in maceral.In bright coal and semi-bright coal,macropores and micropores are relatively developed,while in dull coal,pore evolution shows lag characteristics.Third,coal lithotype and thermal evolution degree are the primary factors controlling coal pore volume and specific surface area.Fourth,the models of four thermal evolution stages of coal reservoir pores are established.It is revealed that the evolution process of pore structures in coal reservoirs is the competitive outcome of primary pore alteration and secondary pore formation.In conclusion,the research results are beneficial for deepening the understanding of the geological evolution patterns of pores in different coal lithotypes,and further provide a reference for evaluating the carriers and mature intervals of free gas and adsorbed gas enrichment in deep coal seams,as well as for deep CBM accumulation research,exploration,and evaluation.