Structural and thermal control of enrichment conditions of coal measure gases in Linxing block of eastern Ordos Basin

Linxing block,located in the eastern part of the Ordos basin,is one of the key areas of exploration and de- velopment of unconventional gases in coal series,in China. This paper discusses the paragenesis and enrichment law of coal measure gases and their control factors of Linxing block from the point of tectonic-thermal effect. Impacted by the intrusion of Zijinshan magmatic rock mass,the regional monocline tectonic pattern was superimposed into three second- ary structural units,named as central uplift zone,annular fold zone and monocline structural belt,and the difference of deformation characteristics in secondary tectonic units determined the different paragenesis types and enrichment fea- tures of coal measure gases. The geothermal gradient and reservoir pressure gradient in coal series decreased in order from the central uplift belt,which leads to the lower gas content of coalbed methane and shale gas,but tight sandstone gas showed opposite trend. The distribution of groundwater salinity showed that the hydrodynamic condition of the an- nular fold belt was the weakest so that where was favorable for the adsorption gas preservation. According to the char- acteristics of main control factors of gas enrichment in different secondary structural units,the coal measure gases reservoir models have been proposed with “ magmatic intrusive type→syncline and hydraulic sealing type→low-angled monocline and lithologic sealing type” which correspond to central uplift zone,annular fold zone and monocline struc- tural belt.