Control factors of mesopore-macropore development in medium-and low-rank coal in Cubey Coalfield

The Cubey Coalfield is one of the key targets for coalbed methane (CBM) exploration in Xinjiang Uygur Autonomous Region.The meso-pores and macro-pores are the main seepage channels in coal reservoir and their development degrees are key factors determining coal reservoir development potential.In this paper,in order to clarify the factors controlling the development of mesopore and macropore in the medium and low-rank coals of the Cubey Coalfield,coal samples drilled from nine CBM wells were collected,and experiments including high-pressure mercury intrusion porosimetry tests (forty-five samples),coal maceral analyses (thirty-one samples),and maturity tests (thirty-two samples) were carried out.In addition,coal structural characteristics of forty-five samples were described.Based on the analyses above,the volumes of meso-pore and macro-pore were extracted,and the geological factors controlling their development degrees were discussed.The results showed that: ① the vitrinite content and maturity of coal had a weak influence on the development of meso-pores and macro-pores; ② the meso-pore and macro-pore volumes of primary structural coal,cataclastic coal and pulverized coal were close,while those of mylonitized coal were relatively greater;③ the complexities of meso-pore and macro-pore structure tended to increase with the increased of vitrinite content when vitrinite content was greater than 70%;④ the coal structure had a slight influence on the complexity of meso-pore structure,while it was positively correlated with the complexity of macro-pore structure; ⑤ maturity had an obvious controlling effect on the complexity of meso-pore structure,while its effect on the structural complexity of macro-pore was weak.Results of this study can provide theoretical support for the scientific evaluation of high permeability coal reservoir in the Cubey Coalfield.