鄂尔多斯盆地东缘临兴地区煤系气富集的构造-热作用控制

鄂尔多斯盆地东缘的临兴地区是我国煤系三气勘探开发的重点地区之一,从构造-热作用控制的角度,探讨临兴地区煤系气共生富集规律及其控制因素。受紫金山岩体侵入影响,区域单斜构造格局分划为中央隆起带、环形褶皱带和单斜构造带3个次级构造单元,各次级构造单元构造变形特征差异,决定了煤系气共生组合类型和煤系气富集规律。煤系地温梯度和储层压力梯度由中央隆起带向外逐渐降低,导致煤层气、页岩气等吸附气含气量依次降低,致密砂岩气则呈现出相反趋势。地下水矿化度分布特征表明环形褶皱带内水动力条件最弱,有利于吸附气保存。根据不同次级构造单元内煤系气富集主控因素特征,提出与中央隆起带、环形褶皱带、单斜构造带相对应的"岩浆侵入型→向斜与水力封堵型→缓倾单斜与岩性封堵型"的煤系气富集成藏模式。

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 development 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 secondary 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 features 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 annular fold belt was the weakest so that where was favorable for the adsorption gas preservation.According to the characteristics 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 structural belt.