鄂尔多斯盆地东缘构造-水文地质控气特征

摘要

基于大量野外地质工作,结合钻孔抽水试验资料分析,探讨了鄂尔多斯盆地东缘构造、水文地质条件及其对煤层气保存的控制特征.结果显示,盆地边界近NS向的压性断裂和褶皱构造发育,构造变形程度向盆地内部逐渐减弱,即盆地边缘和内部的构造条件均有利于煤层气保存.依据构造、地下水补给及排泄条件和地貌等特征,研究区可划分为5个水文地质单元,西南部韩城单元的水动力条件强于东部各水文地质单元,东部各单元中又以柳林泉流域水动力条件最强,这种差异在构造背景上的叠加,导致煤层气保存条件发生分异.中部黄河东断凹单元煤层含气量随埋藏深度的加深而增高,北部柳林单元在柳林泉以西发育有利煤层气保存的地下水动力场条件,中南部龙门山单元北部的地下水动力条件可能有利于煤层气保存,西南部韩城单元西北段地下水处于滞流环境而使煤层气保存条件较好.%Based on field investigation and data of borehole pumping test, the structure, hydrogeology and their controls to the coalbed methane (CBM) preservation in eastern margin of the Ordos basin were discussed. Results showed that the compression faults and folds with nearly south-north direction develop well in the basin margins, and the tectonic deformation weaken gradually towards the center of the basin, which indicates the structure both in the margin and center of the basin is all conducive to the CBM preservation. Five hydrological units in the area were distinguished based on the geomorphological and geological conditions such as the structure and groundwater recharge and discharge. Hydrodynamic in southwestern Hancheng unit is stronger than that in other units in the eastern, and that in the Liulin unit is strongest among the eastern units. Superposition of the hydrodynamic variation on the tectonic setting makes the differentiation of CBM preservation conditions. CBM content in middle Yellow River depression increases with the increase of the burial depth. Hydrodynamic favorable to CBM preservation in northern Liulin unit occurs at the western part of the Liulin Spring in the unit. Groundwater dynamic at the northern part of the Longmenshan unit may be favorable to CBM preservation. Good CBM preservation occurs in the northwest part of the Hancheng unit due to the stagnant groundwater.