鄂尔多斯盆地北部上古生界煤成气及其砂岩气藏成藏模式

鄂尔多斯盆地北部上古生界地层中广泛发育的煤层是大型气田形成的物质基础,煤层埋深为2.2~2.8 km,厚度为22~49 m,镜质体反射率为0.6%~2.5%,属长焰煤—贫煤;煤层是良好的烃源岩,其平均生烃强度为23.52×108m3/km2.煤层、砂岩储层和顶部上石盒子区域性泥岩盖层的良好空间配置是上古生界煤成气砂岩气藏形成的关键.描述了该地区上古生界砂岩和泥岩中2种高角度裂缝特征,指出了裂缝的形成时期及其在煤成气成藏中的运移通道作用.最后将该地区煤成气藏近源型成藏模式细分为近源-源内聚集型和近源-裂缝运移型.

Coal-formed gas of upper Paleozoic in the north of Ordos Basin and its pool forming modes

The coal seam developing in the upper Paleozoic in the north of Ordos Basin is the material basis of forming large scale gas-fields.The buried depth of the coal seam is in 2.2~2.8 km,its thickness is in 22～49 m,and its vitrinite reflectance is between 0.6% and 2.5%.The property of the coal is between flame coal and lean coal.The coal seam is good hydrocarbon source rock,and its average hydrocarbon-generating intensity is 23.52 × 108 m3/km2.The good space matching among the coal seam,the sandstone reservoir and the mudstone cap-rock in upper Shihezi Formation is the key to the formation of the coal-formed gas sandstone reservoir in the upper Paleozoic.The features of two types of high-angle fractures in the sandstone and the mudstone in the upper Paleozoic show their role in the fracture formation period and migration channel in the coal-formed gas accumulation.The near-source accumulation mode of the coal-formed gas is further classified into near-source-source-inner accumulation type and near-source——fracture migration type.