黔西比德-三塘盆地煤层群含气系统类型及其形成机理

Type and geological controls of coalbed methane-bearing system under coal seam groups form Bide-Santang basin,Western Guizhou

黔西比德-三塘盆地上二叠统煤层群具有特殊的煤层气含气系统.基于实测资料分析,根据煤层群垂向层位含气量波动性强弱和含气量梯度大小作为划分研究区煤层群含气系统类型的指标,将研究区划分为3类煤层气系统.研究表明:中部区域波动性最为复杂,含气量梯度中等;东部区域波动性较简单,含气量梯度最大;西部区域含气量梯度最小,波动亦简单,3类系统总体上显示为随层位降低煤层含气量增加.控制含气量波动性变化的主要因素是含煤地层的层序结构,东、西区域灰岩和细砂岩发育,封闭性较弱,含气系统较为简单;中部地区泥质岩发育,封闭性好,存在多套含气系统.钻孔抽水资料佐证了中部地区存在多套含气系统,各系统内部视储层压力随埋深增加而增大,这是煤层群含气量总体随埋深增加而增大的间接控制因素.

There is a particular coalbed methane（CBM）-bearing system in the Upper Permian coal seam groups form the Bide-Santang basin,Western Guizhou.Based on the measured data,the CBM content fluctuating curve and gas vertical gradient were used to distinguish three types of the CBM-bearing system.The results show that the fluctuation character is complex in middle part of the basin with middle CBM content gradient,and relatively simple in eastern part with the largest CBM content gradient and western part with the lowest gradient.In general,the CBM content increase with the falling down of coal seam horizon.The key geological control of the CBM content fluctuation is the structure of coal-bearing strata sequence.The limestone and sandstone developed well in the eastern and western parts,and the CBM cap rocks are relatively open and simple.The mudstone developed in the middle part,and the cap rocks are closed and multi-CBM-bearing system which has been testified with the borehole pumping-water information.Inside each CBM-bearing system,the apparent reservoir pressure increases with increasing of burial depth,which results indirectly in the increasing of CBM content with the increasing of depth.