淮南煤田煤层气成藏动力学系统的机制与地质模型研究

淮南煤田由次生生物成因和热成因气组成的混合型煤层气藏,受各种地质和水文地质条件的影响和控制。本文通过热流场和地温场、古构造应力场和原地应力场以及地下水动力场的系统分析,探讨了煤层气成藏动力学系统的形成机制,进而提出了相应的成藏地质模型。淮南煤田的煤层气藏虽然属向斜式(或盆心)聚气模型,但是,该模型强调,作为附加气源的次生生物气的补充,成藏动力学系统演化、构造样式和能量场的耦合关系,是混合型煤层气富集成藏的主因。 

A study on the mechanism and geological model of CBM reservoir-forming dynamic system in Huainan Coalfield

The Permian coalbed methane(CBM) reservoir with mixed secondary biogenic and thermogenic gas in the Huainan Coalfield, Anhui Province, is affected by complex geological and hydrogeological factors. The purpose of this paper is to provide a basic understanding of CBM reservoir-forming dynamic system mechanism, which involved the thermal flux and geotemperature fields, palaeo- and modern tectonic stress fields, and hydrodynamic field. Although the CBM reservoir in the Huainan Coalfield is usually considered as a conceptual model of synformal or/and basin-centered gas accumulation, but this model emphases that, after Permian coals reaching their maturity, it had suffered uplift in large scale, unload and reburied. Due to lose of thermogenic adsorbed gas, it resulted in that the coal reservoirs were in the unsaturated status. When meteoric water seeps through coal beds, in them secondary biogenic methane and CO₂ are generated from wet gas and other organic matter by the metabolism of bacteria activity. In the process of groundwater centripetal drainage, the secondary biogenic gas carried in the front (or "washing" soluble gas) was pushed to the impermeable barrier or/and the structure hinge line, and was stayed and resorbed by coal matrix, or/and was full in coal cleats, which supplements the coal reservoirs and leads to the increase of gas content and saturation, and then, it was enriched and formed CBM reservoir. Therefore, the CBM accumulation in the Huainan Coalfield is mainly controlled by the evolution of coal reservoir-forming dynamic system, and the coupling relationship between the tectonic style and the energy fields.