鄂尔多斯盆地煤岩气储层孔裂隙结构类型划分及其勘探意义OA

The Ordos Basin harbors immense resource potential of coal-rock gas.At present,however,there is a lack of thorough research on the maceral characteristics,pore classification,pore structure characterization,and controlling mechanisms on gas occurrence in coal-rock gas reservoirs.Taking the deep coal reservoirs of Carboniferous Benxi Formation in the Ordos Basin as the research object,this paper systematically develops a set of full-scale quantitative characterization method for the pore-fracture structures in coal-rock gas reservoirs by means of various experimental methods such as coal petrographic and quality analysis,scanning electron microscopy(SEM),Nano-scale CT scanning and 3D reconstruction,gas adsorption,and high-pressure mercury intrusion(HPMI).In addition,the types,distribution characteristics and controlling factors of the microscopic pore-fracture structures are systematically revealed,and the pore-fracture structures in coal-rock gas reservoirs are classified into three types.The following results are obtained.First,the Benxi Formation coal reservoirs are mainly composed of bright and semi-bright coals with medium to high evolution degree,where primary structures are dominant,and pore-fracture structures are dominated by organic matter pores and cellular pores.Second,the pore size distribution in the Benxi Formation coal reservoirs is primarily micropores(65.0%of total pore volume),followed by microfractures(25.4%of total pore volume),with macropores and mesopores underdeveloped,overall presenting the characteristics of dual pore-fracture structures.Third,the pore-fracture structures are jointly controlled by metamorphism degree,vitrinite content,and ash yield.The northern part of the study area is generally dominated by the"U"-shaped bimodal-microfracture predominance type;the central part mainly develops the"U"-shaped bimodal-micropore and microfracture predominance type,which has the greatest exploration and development potential;and the southern part is mainly characterized by the"U"-shaped bimodal-micropore predominance type.Fourth,the exploration potential and fracture network demand for development and production of coal-rock gas are controlled by pore-fracture structure types and total gas content.In conclusion,this study provides important guidance for the exploration direction and sweet spot prediction of coal-rock gas in the Ordos Basin.