The shale gas accumulation in the Sinian Doushantuo Formation in the Baojing region,Hunan

The development and distribution of the shale reservoirs in the Sinian Doushantuo Formation in the Baojing region, Hunan are examined on the basis of field geological investigation and analytical results of core samples so as to evaluate the exploration potential of the shale gas in the Doushantuo Formation, where there developed grey dolomitic limestone, black carbonaceous mudstone, black siliceous rocks, dark grey micritic limestone and dark grey calcium-bearing carbonaceous mudstone of the passive continental margin shallow shelf-slope facies. These shale reservoirs have tremendous thickness (150-200 m), higher organic carbon contents (4.07%-10.25%), and higher maturity (3.78%-4.97%), moderate porosity (0.19%-2.355%) and extremely low permeability (0.0005257-0.5910081 mD). The contents of the brittle minerals in the shale reservoirs are relatively higher, varying from 55.9% to 84.5%, and consist dominantly of quartz, calcite, pyrite and plagioclase, while the contents of the clay minerals are relatively lower, ranging from 16.5% to 44.1%, and mainly composed of illite, chlorite, mixed illite-montmorillonite beds and chlorite-montmorillonite beds, suggesting that the Sinian Doushantuo Formation went through the late diagenetic stages. The reservoir spaces include solution openings, organic matter solution openings, intercrystalline pores in pyrite and clay minerals, diagenetic cleavage cracks and structural microfractures. It is concluded from the results of research cited above that the Doushantuo Formation in the Baojing region is of favourable geological conditions for the shale gas accumulation, and thus may have the potential for further exploration in this region.