煤层气藏边界类型、成藏主控因素及富集区预测

Coalbed gas reservoirs:Boundary types,main controlling factors of gas pooling,and forecast of gas-rich areas

如何定义煤层气藏、如何界定气藏边界是认识煤层气藏的关键,要评价煤层气富集区首先要找出控制其成藏的主要因素。为此,结合我国含煤盆地的典型煤层气藏特征,围绕煤层气藏边界类型、成藏主控因素进行了探讨,并预测了沁水、鄂尔多斯、准噶尔盆地的煤层气富集区。结论认为:①煤层气藏的边界是煤层气藏划分的前提,煤层气藏主要有5种地质边界类型:水动力边界、风氧化带边界、物性边界、断层边界和岩性边界;②煤层气藏的形成经历了煤层气的生成和吸附、煤层的吸附能力增加和煤层气的解吸—扩散和保存阶段;③保存阶段是成藏的关键,区域构造演化、水动力条件和封闭条件是主要的成藏控制因素。进而在沁水盆地、鄂尔多斯盆地和准噶尔盆地优选出9个煤层气有利富集区:晋城、阳城、安泽、阳泉、大宁—吉县、韩城、吴堡、准南、阜康。

How to define a coalbed gas reservoir and identify its boundary is important for researchers to know well about the coalbed gas reservoirs,and a better evaluation on the coalbed gas-rich areas relies mostly on a better understanding of the main controlling factors of coalbed gas pooling.Therefore,in combination with the characteristics of typical coalbed gas reservoirs in some coal-bearing basins in China,this paper discussed the boundary types and the main controlling factors of coalbed gas reservoirs,and forecast the coalbed gas-rich areas in the Qingshui,Ordos,and Junggar basins.The conclusion was presented as follows:a.the boundary of a coalbed gas reservoir is the prerequisite of classifying the coalbed gas reservoir types,and five boundary types include hydrodynamic boundary,the boundary of efflorescent oxygenized belts,petrophysical boundary,fault boundary,and lithological boundary;b.a coalbed gas reservoir came into being after the following stages:methane gas first generated and was adsorbed in coalbed layers,then the adsorption ability of coalbed layers increased,and gas was preserved after desorption-diffusion-migration;c.the preservation stage plays an important role in a coalbed gas reservoir,and regional structure evolution,hydrodynamic and sealing conditions are the main controlling factors.Furthermore,nine optimal coalbed gas-rich areas were selected from the Qingshui,Ordos,and Junggar basins:Jincheng,Yangcheng,Anze,Yangquan,Daning-Jixian,Hancheng,Wubao,Zhunnan,Fukang.