新疆后峡盆地中–低阶煤煤层气成藏模式

Accumulation mode of middle-low rank coalbed methane in Houxia Basin,Xinjiang

  • 摘要: 低阶煤层气在国外有规模开发成功的案例,我国低阶煤层气资源丰富,但其勘探开发进展缓慢。新疆后峡盆地煤层气勘探程度较低,为进一步认识后峡盆地中–低阶煤煤层气成藏条件,指导勘探实践,根据研究区内地震、地质及已钻探井的煤岩分析化验和排采生产资料进行总结分析。结果表明,该区构造较为复杂,煤层厚度较大(4.1~24.3 m),发育较稳定,含气量差异较大(1.16~12.30 m3/t),物性较好,渗透率(1.61~13.30)×10−3 μm2,渗透性较好;并且存在热成因、次生热成因、混合成因及生物成因4种煤层气成因类型,结合构造演化、水文地质及煤层顶底板保存条件,形成了深层热成因、常规圈闭次生热成因及中浅斜坡生物气3种成藏模式,每一种成藏模式代表了不同的煤层气富集过程。认为研究区中–低阶煤煤层气在匹配的构造、水文及顶底板封盖条件下能够形成有利的资源富集区;3种成藏模式中,深层热成因及常规圈闭次生热成因成藏模式更有利于聚集成藏,其对应的区域是今后勘探开发有利区。

     

    Abstract: There are successful cases of large-scale CBM development of low-rank coal abroad. Though China is rich in low-rank CBM resources, their exploration and development progress is slow. Considering the low exploration degree and for the purpose of further understanding the accumulation conditions of medium-low rank CBM and guiding exploration practice in Houxia Basin, seismic and geological analysis, as well as coal petrography analysis and drainage production data of drilled wells are carried out in the study area. The results show that the coal seams are characterized by complex structure, large thickness (4.1-24.3 m), stable development, large difference in gas content (1.16-12.30 m3/t), good physical properties and large permeability (1.61-13.30)×10−3 μm2. There are four genetic types of CBM: thermal origin, secondary thermal origin, mixed origin and biological origin. Under this condition, combined with structural evolution, hydrogeology and preservation conditions of the coal seam roof and floor, three accumulation models of deep thermal origin, secondary thermal origin of conventional traps and medium shallow slope biogenic gas are formed. Each mode represents the concentration processes of different types CBM. It is considered that the medium-low rank CBM in this study area can form a favorable resource concentration area under the matched structural, hydrological, and roof and floor sealing conditions. Among the accumulation modes, deep thermal origin and secondary thermal origin of conventional traps are more favorable for accumulation, and the corresponding areas are favorable for future exploration and development.

     

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