无烟煤煤层气成藏与产气机理研究——以沁水盆地无烟煤为例

煤层气成藏和产气必须具备6个方面的必要条件:①生气母质;②储气空间;③吸附动力;④导流通道;⑤驱动能量;⑥煤体结构.当前的气藏潜力判定条件主要包括等温吸附性质、导流性质、含气性质和吸附与驱动能量,吸附常数、渗透率、含气量以及储层压力是4个重要的代表性参数.在以4项参数为表征时,常规无烟煤作为煤层气储层存在着很大的地质缺陷,因而无法成藏和产气.而沁水无烟煤则具备良好的沉积、构造和地热作用历史配置,用当前较为成熟的中阶煤产气理论来判定,由其4项参数所定性的气藏是典型的优质商业气藏.研究结果表明,地壳抬升造成的浅埋、莫霍面上拱造成的快速热变、区域拉张应力以及特殊的汇水构造是沁水无烟煤煤层气成藏和产气的根本原因.

Coalbed methane reservoir and gas production mechanism in anthracite coalbeds

The necessary conditions for coalbed methane (CBM) reservoir and gas production include gas prone organic matters,gas storage space,absorbing power,flow channels,driving capacity and coal reservoir stimulation.At present,the diagnostic criteria for gas reservoir mainly include isothermal adsorption property,flowing transferability,gas content,absorbing and driving power.The adsorption constant,permeability,gas content and reservoir pressure are the key indexes for evaluating the potential of a CBM reservoir.In terms of these four indexes,the normal anthracite has no potential for gas reservoir and production.The evaluation result of Qinshui anthracite with middle ranked coal theory shows that it has good sedimentary tectonic and geothermal history.The evaluation with the four indexes shows that anthracite in Qinshui Basin has good commercial gas production.The crustal movement,magma intrusion and sedimentation are very well stacked during the coalification process in Qinshui Basin.The four elements are attributed to the commercial production of CBM in Qinshui anthracite coal,including shallowly buried coal seam resulting from crustal movement upward before the second gas generating rush,short-time strong geothermal coal alteration due to Mohole layer up-bending,regionally distributed extensional crustal stress and geological structure for water pressurization.