国内外低煤阶煤层气地质差异性与聚气模式探讨

全球低煤阶煤层气资源丰富，煤层厚度大、含气量偏低、渗透性好、单井产量高，成为煤层气地质评价与产业发展的重点。国外低煤阶煤层气产量已占煤层气总产量的80%，而中国仅为1.8%。通过国内外低煤阶煤层气资源分布、勘探开发进展、地质差异性、成藏共性特点及聚气模式等研究，得出以下结论：中国低煤阶煤层气资源丰富，主要赋存于新疆侏罗系、内蒙古东部白垩系及中国东北地区古近系煤层；在以挤压、碰撞为主的构造演化背景下，中国低煤阶煤层物性显著变差，湿润气候区降雨或干旱气候区山前冰川融水的补给使煤层产生次生生物气，但区域动力变质、岩浆接触热变质所产生的热成因气，使新疆、中国东北地区低煤阶煤层含气量普遍偏高；地质差异性导致中国低煤阶煤层气风化带深、聚气模式多样、产气量偏低；气候条件、构造演化对低煤阶煤层气聚集影响显著，“淡水补给生气”、“圈闭聚气”是国内外低煤阶煤层气成藏且气井高产的共性主控因素，但生气、聚气阶段的差异会形成不同特点的煤层气藏；中国低煤阶煤层气“甜点”区评价应注重一定埋深、高煤层水矿化度、单斜/向斜的承压水滞留区或断块、背斜等圈闭部位。

Geological differences and accumulation modes between domestic and foreign low-rank coalbed methane

Global low-rank coalbed methane(CBM) resources are abundant. The coal seam has large thickness, low gas content and good permeability, which lead to high production. Foreign low-rank CBM accounts for 80% of total production, while China is 1.8%. Based on the study of the resources characteristics, exploration and development progress, geological differences and accumulation models, the conclusions were obtained. Abundant low-rank CBM are mainly found in Jurassic, Cretaceous and Paleogene coal seam in Xinjiang, eastern Inner Mongolia, and Northeast China. The plate tectonic evolution is dominated by extrusion and collision in China, the physical properties of coal seams have deteriorated significantly. Regional dynamic metamorphism and magma contact thermal metamorphism have caused thermogenic gas in Xinjiang and Northeast China, and secondary biogas generated by rainfall or glacial meltwater in mountain fronts, which lead to high gas content. Geological differences result in the deep weathering zone, diversified gas accumulation modes, and low gas production in China. Climatic conditions and tectonic evolution have a significant impact on the accumulation of low-rank CBM, whose characteristics are “freshwater supply gas” and “trap accumulation gas”. The differences of gas generation and accumulation stages will form different characteristics of CBM reservoirs. China's low-rank CBM exploration should focus on certain depth, high salinity water, monocline/syncline confined water retention area or trapped parts such as fault blocks and anticline.