韩城煤层气田水文地质旋回对煤层气的影响

通过对韩城煤层气田水文地质旋回划分、构造演化和延续时间系数及含气量的综合分析，探讨了韩城煤层气田水文地质旋回对煤层气的影响。结果表明：研究区自下而上划分为4个水文地质旋回，其中第Ⅰ水文地质旋回（∈-C1）只构成气田的基底，对煤层气的生成和吸附无影响；石炭-二叠系煤系地层在第Ⅱ水文地质旋回（C2-T3）沉积；第Ⅲ水文地质旋回（J1-J3）对煤层热成熟有一定的促进作用；煤系地层在第Ⅳ水文地质旋回（K1-Q）经过了短时间高温条件下的变质作用，是煤层气生成的关键时期，历史最大含气量达到22 m 3/t。通过该区煤层等温吸附曲线的特征判断，第Ⅳ水文地质旋回渗入水文地质阶段约20 MPa煤系地层压力的降低幅度，只造成原始最大含气量18%左右的解吸气量，没有改变研究区煤层气吸附量大和资源丰富的基本特征。水文地质旋回分析方法从成因机制上说明了韩城煤层气田具有较大的资源潜力。

Influence of hydrogeological cycles on CBM in Hancheng CBM field,Central China

Through comprehensive analysis of hydrogeological cycles，tectonic evolution，duration factor and gas content in Hancheng CBM field，the effects of hydrogeological cycle on CBM in Hancheng CBM field were discussed.The results show that the study area is divided into four hydrogeological cycles from bottom to top.The first hydrogeological cycle(∈-C1) has little influence on CBM’s generation and adsorption and only constitutes bottom aquifer of the CBM field.Coal bearing strata of Carboniferous Permian deposited during the second hydrogeological cycle（C2-T3）.During the third hydrogeological cycle（J1-J3），coal beds were buried to be primarily thermally matured.During the fourth hydrogeological cycle(K1-Q），Carboniferous Permian coal beds reached their biggest bury depth and gas was generated in great quantity with historically maximum gas content being about 22 m 3/t.According to the adsorption isothermal curve of core samples of the studied area，only about 18% of historically maximum adsorption gas was released due to pressure decrease of about 20 MPa during infiltration stage of the fourth hydrogeological cycle due to uplift and erosion of overburden formation，illustrating Hancheng CBM field has rich resource potential.