沁水盆地榆社-武乡区块深部煤层气赋存条件及开发甜点预测

Occurrence conditions and development sweet spots prediction of deep coalbed methane in Yushe⁃Wuxiang block of Qinshui Basin

沁水盆地榆社-武乡区块深部煤层气富集成藏受多因素耦合作用,深部条件的特殊性使其选区不能完全参照浅部地质评价技术,亟需从地质-工程角度对区块进行开发甜点区优选,满足实际生产需要。以3#煤层为目的层,从构造与水动力、地应力、煤储层含气性、孔渗性、煤体结构及力学性质等条件出发,剖析深部煤层气富集特点,运用多层次模糊数学评价法对区块进行甜点优选。结果表明:3#煤层煤体结构以Ⅰ类原生结构煤为主,具有泊松比小、弹性模量大、脆度指数高、含气性良好的特点,煤层厚度0.25~5.19 m,平均1.59 m,含气量16.5~25.5 m^(3)/t,平均19.84 m^(3)/t;研究区褶皱与断层较为发育,煤层顶板岩性以泥岩为主,地下水径流条件差;深部地应力状态表现为σV(垂直压力)>σH(最大水平压力)>σh(最小水平压力);3#煤层属低孔、低渗储层,微小孔发育,渗透率平均为0.183×10^(-3)μm^(2);根据综合评价得分划分4类甜点区,其中区块中西部和L1302井附近为开发甜点区。研究成果对榆社-武乡区块深部煤层气下一步勘探开发具有指导意义。

The enrichment and accumulation of deep coalbed methane of Yushe-Wuxiang block in Qinshui Basin are affected by coupling of multiple factors,and the particularity of deep conditions makes its areaselection cannot fully refer to shallow geological evaluation technology.Therefore,the development sweet spots optimization from perspective of geology-engineering is urgently needed so as to meet actual production requirements.Taking 3#coal seam as target layer,The enrichment characteristics of deep coalbed methane are analyzed on the basis of condi‑tions including structure and hydrodynamics,in-situ stress,gas-bearing properties of coal reservoir,porosity and permeability,coal structure and mechanical properties.The optimization of sweet spots in this block is carried out by using multi-level fuzzy mathematical evaluation method.The results show that the main coal structure of 3#coal seam is Class I primary structure,which is characterized by low Poisson ratio,high elastic modulus,high brittle‑ness index and good gas-bearing properties.The thickness of coal seam is 0.25~5.19 m with average of 1.59 m,and gas content is 16.5~25.5 m^(3)/t with average of 19.84 m3/t.Folds and faults are relatively well developed in studied ar‑ea,roof lithology of coal seam is principally mudstone,and groundwater flow conditions are poor.Deep in-situ stress state isσV(vertical pressure)>σH(maximum horizontal pressure)>σh(minimum horizontal pressure).3#coal seam is low-porosity and low-permeability reservoir,with micro pores well developed and average permeability of 0.183×10^(−3)μm^(2).According to comprehensive evaluation scores,the sweet spots are divided into 4 types,in which the development sweet spots are located in central and western parts of the block and near Well L1302.The re‑search results have guiding significance for further exploration and development of deep coalbed methane of Wuxiang-Yushe block in Qinshui Basin.