Yin Shuai, Ding Wen-long, Dai Peng, Wang Ru-yue, Yang Wen-na
Gas logging abnormality is very common in Taiyuan Formation,Shanxi Formation and Lower Shihezi Formation in Qinshui Basin,which has a high potential for gas exploration.But there is a huge difference in the extent of hydrocarbon accumulation,which is dominated by fracture development degree.Inversion of rock pore aspect ratio has reference value for basic research of hole seam,seismic inversion,physical simulation,gas channel conservation and wellblock optimization.Making a coalbed methane Well in south of Shanxi Formation in Fanzhuang block,Guxian well block of Qinnan as an example,based on optimization algorithm,we extract the matrix mineral and rock skeleton modulus of coal and its roof sandstone and sandy mudstone,then inverse the pore aspect ratio using DEM theory model.It shows,the nearly spherical pore space system is dominant in the studied coal rock;the roof dense clayey sandstone is given priority to micro cracks;there are multiple space systems of pore and fracture in sandy mudstone.The use of this method can effectively identify the formation with fracture development,the coincidence rate was 92%.For sandy shale,sand or mud package type rock,micro cracks mainly exist in the sand, α is negatively related to the porosity of rock,and positively related to shale content in this kind of rock.Regardless of sandstone,mudstone or coal rock,communication or drainage capacity of fracture system is superior to the pore system.When there are good gas source,drainage system,fracture system and preservation conditions,coal-derived gas reservoir will be formed.Study of α has certain reference value in fracture parameters extraction,rock ability of saving gas,pore communication ability,permeability ability,and gas channel conservation accumulation etc,and it has positive significance to guide CBM or coal-derived gas exploration and development.
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