Geochemical characteristics and hydrocarbon-generation potential of coal- bearing source rocks in the deep part of Panxie mining area,Huainan

In order to ascertain the hydrocarbon generation potential of the deep part of Panxie mining area in Huainan coalfield,on the basis of sampling the source rocks of coal measures,some organic geochemical methods such as total organic carbon content ( TOC),chloroform bitumen “ A”,rock pyrolysis,kerogen carbon isotope and vitrinite reflectance were used,combined with the achievements of deep coal exploration,to investigate the geochemical characteris- tics,thermal evolution and hydrocarbon generation combination characteristics of coal-bearing source rocks in the deep part of Huainan mining area. The geochemical test results show that the organic kerogen in coal measures belongs to type Ⅱ2 -Ⅲ,with a small amount of type Ⅱ1 ,and has a good potential for gas generation. The TOCs of shale in Upper Shihezi Formation,Lower Shihezi Formation and Shanxi Formation all meet the standard of medium hydrocarbon source rocks,the chloroform asphalt “ A” also meets the standard of good hy-drocarbon source rocks,the S1 +S2 of shale in Upper Shihezi Formation and Shanxi Formation meets the standard of medium hydrocarbon source rocks,and the S1 +S2 of shale in Lower Shihezi Formation meets the standard of good hydrocarbon source rocks. Therefore,all indexes of or- ganic matter abundance in shale have reached the standard of medium or good hydrocarbon source rocks,and the total organic carbon content in coal seam is above 60% ,which indicates that the organic matter in deep coal measures in Panxie mining area has high primary hydrocarbon generation ability. Based on the analysis of organic geochemistry and gas logging characteristics of coal-bearing source rocks in PQ-1 well,combining with the borehole columnar of deep coal exploration,and taking the thick coal seam and shale as the target horizon,three sets of stable hydrocarbon-gener- ating combinations were divided in the deep part of Panxie mining area. Combination 1 is located in the middle-lower part of the upper segment of Upper Shihezi Formation,with a thickness of about 40 -60 m,and is a good shale gas- coalbed methane co-generation reservoir. Combination 2 is located in the upper part of Lower Shihezi Formation,with a thickness of about 60-150 m,and dominated by coalbed methane and supplemented by shale gas. Combination 3 is lo- cated at the bottom of Shanxi Formation,with a thickness of about 20-35 m,and dominated by coalbed methane and supplemented by shale gas.