潮水盆地煤层气储层特征及勘探潜力

为查明河西走廊北部潮水盆地煤层气富集规律及成藏主控因素，从煤层分布特征、煤岩煤质特征、煤岩演化程度、煤层等温吸附特征等方面，分析了该区煤层气的储层特征。结果表明：潮水盆地煤岩演化程度低，处于低煤阶褐煤-气煤演化阶段；煤层兰氏压力高（5.95~6.90 MPa），利于煤层气的解吸。通过进一步的现场解吸实验，测试了该区A1、A3井煤层的含气量（分别为0.25、0.56 m³/t），并从生气条件、保存条件两个方面分析得出导致其煤层含气量低的主要原因为：①盆地发育拉张性正断层，成为煤层气逸散的通道；②盆地西部缺少区域性盖层，直接盖层为砂岩，导致煤层气散失；③缺少生物气的补充。最后，综合评价了各构造单元的勘探潜力，认为红柳园坳陷生物气特征明显且顶板盖层封盖性好，可作为该区下一步煤层气勘探的靶区。

Characteristics of CBM gas reservoirs and their exploration potential in the Chaoshui Basin, northern Hexi Corridor

In order to enhance the understanding of the CBM enrichment pattern and the major controlling factors of CBM accumulation in the Chaoshui Basin, northern Hexi Corridor, we first analyzed the characteristics of CBM gas reservoirs in the study area in the aspects of coal layer distribution, coal rock quality, evolution degree of coal rocks, and isothermal adsorption features of coal beds. And we drew a conclusion that the coal rocks in this basin are low in thermal evolution degree at a stage of low rank of lignite to gas coals, and are high in Langmuir pressures in the range of 5.95 ~ 6.90 MPa, which provides a favorable condition for CBM desorption. Then the gas contents of the coal beds in A1 and A3 wells in this area were tested to be 0.25 and 0.56 m³/t respectively through field desorption experiments. The causes of such low gas content in the coal layers were analyzed in respect of gas generation and preservation conditions. The following conclusions were obtained. (1) Extensional faults are developed in the basin and act as pathways for CBM gas escaping. (2) No regional seals exist in the western part of the basin and the direct overlying strata are sandstones, which leads to the escaping of CBM gas. (3) There is no biogas charging. Finally the exploration potential of each structural unit was comprehensively evaluated and the Hongliuyuan depression was thought to have prominent features of biogas with perfect caprocks so as to be selected as the target of CBM exploration in the future.