黔西上二叠统含煤层气系统特征及其沉积控制

The Upper Permian Coalbed Methane Bearing System and its Sedimentary Control in Western Guizhou, China

基于黔西地区晚二叠世含煤地层钻井岩芯观察及样品分析测试结果,指出沉积环境对"多层叠置独立含煤层气系统"的发育具显著的控制作用。研究结果表明,含煤岩系中低渗透岩层的分布对"多层叠置独立含煤层气系统"的形成具有分划性的阻隔作用,这种分划性隔水阻气的发育受控于沉积环境,从三角洲平原相区至三角洲前缘相区含煤地层中具低孔渗透条件的隔水阻气层渐趋发育,导致垂向含煤层气系统渐趋复杂。三角洲平原相区偏于氧化环境,不利于准同生成岩—早成岩作用阶段菱铁矿和黄铁矿的形成,层序内最大海侵面附近泥岩的封堵性能相对减弱,使得原本相对孤立的含气组合彼此连通构成相对统一的含气系统,垂向含煤层气系统相对简单;而三角洲前缘相区含煤地层中具低孔渗透条件的隔水阻气层相对发育,垂向含煤层气系统较为复杂。

Based on the observation of drilling cores and lab analysis, it is indicated that the formation of ＂unattached multiple superimposed coalbed-methane system＂ is controlled by sedimentary environment remarkably. This study demonstrates that the distribution of low-permeability rocks in coal-bearing strata plays a part of separating in the formation of ＂unattached multiple superimposed coalbed-methane system＂. The development of impermeable gas barrier is controlled by sedimentary environments, under which impermeable gas barrier of low porosity and low permeability in coal-bearing strata tends to form in the area from delta plain facies to delta front facies, resulting in vertical coalbed-methane bearing system becoming gradually complex. For its oxidized environment, delta plain area is not conducive to the formation of siderite and pyrite during the penecontemporaneous diagenesis and early diagenesis stages. The block performance of mudstone is relatively weakened, which is near to the maximum transgressive surface in the sequence, making the unattached coalbed methane bearing system connected to each other, constituting a relatively uniform coalbed methane bearing system. The vertical coalbed methane system is relatively simple in delta plain area. The impermeable gas barrier with low porosity and low permeability in the coal-bearing strata is relative development in the delta front where the vertical coalbed methane bearing system is more complex.