中国煤系气成藏特征及勘探对策

广义的煤系气是指赋存于煤系地层中的全部天然气，而狭义的煤系气则主要指赋存于煤层中的煤层气及其附近致密砂岩储层中的天然气。为了提高煤层气的开发效益，从烃源岩分布、煤与砂岩的组合类型、沉积相、封闭体系等方面分析了我国狭义煤系气的成藏特征及其控制因素。结果表明：①我国含煤盆地煤系地层煤与砂岩组合配置关系多样；②广覆式烃源岩分布为煤系气的富集提供了充足的气源基础；③沉积相控制了煤系气生储盖组合的配置关系，构成煤系气成藏的先天物质基础，河流、三角洲沉积体系煤层和砂岩均发育，是煤系气共生成藏最有利的沉积相带；④封闭体系对煤层（系）气的控制作用贯穿于煤层（系）气生成、聚散、富集及成藏等全过程，可划分出3种煤系气气藏类型--自生自储型煤层气藏、煤层气-砂岩气共生气藏、煤成砂岩气藏，其中前者是目前煤层气勘探开发的主要对象。进而指出了下一步的煤系气勘探方向：①以沁水、鄂尔多斯、准噶尔、海拉尔、鸡西等煤系气资源量较大的盆地为重点，开展煤系气勘探和评价；②针对不同煤系气气藏类型开展有针对性的勘探工作，在浅部自生自储型煤层气富集区进行煤层气勘探，对深部煤层气-砂岩气共生气藏进行煤层气＋砂岩气综合勘探，对煤成砂岩气藏重点开展砂岩气勘探。

Characteristics of coal measure gas accumulation and such gas exploration strategies in China

Coal measure gas is broadly defined as all natural gas occurring in coal measure strata while narrowly defined as the coalbed methane (CBM) in coal beds and the natural gas in the adjacent tight sandstone reservoirs. In this paper, the hydrocarbon accumulation characteristics and control factors of narrowly defined coal measure gas in China were analyzed from the aspects of source rock distribution, coal-sandstone combination type, sedimentary facies and closed system to improve CBM development benefit. And the following research results were obtained. First, there are various coal-sandstone combintion relationships in coal measure strata of coal bearing basins in China. Second, the widely-distributed source rocks provide sufficient gas sources for the enrichment of coal measure gas. Third, sedimentary facies dominate the combination relationships of source–reservoir–caprock assemblages of coal measure gas, so the inborn material base of coal measure gas accumulation is formed. The sedimentary systems of fluvial facies and delta facies are the most favorable sedimentary facies for the paragenesis and accumulation of coal measure gas for their coal beds and sandstones are developed. Fourth, the closed system controls the whole process of generation, enrichment and accumulation of CBM (coal measure gas). Three types of coal measure gas reservoirs are identified: self-source and self-reservoir CBM reservoirs, paragenetic CBM-sandstone gas reservoirs, coal-derived sandstone gas reservoirs, among which the first type is currently the main target of CBM exploration and development. Finally, the next exploration direction of coal measure gas was pointed out as follows. First, the exploration and evaluation of coal measure gas shall be focused on the giant basins with abundant coal measure gas, such as Qinshui, Ordos, Junggar, Hailar and Jixi. Second, coal measure gas reservoirs shall be explored specifically based on different types. It is necessary to carry out CBM exploration in the self-source and self-reservoir CBM enriched zones in the shallow layers, integrated exploration of CBM and sandstone gas in the paragenetic CBM–sandstone gas reservoirs in the deep layers, and sandstone gas exploration in coal-derived sandstone gas reservoirs.