Zhang Baoxin, Deng Ze, Fu Xuehai, Yin Ke
School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China.
Key Laboratory of Coalbed Methane Resources and Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China.
ACS Omega. 2021 Jan 29;6(5):3999-4012. doi: 10.1021/acsomega.0c05930. eCollection 2021 Feb 9.
The daily gas production of a single well (coalbed methane (CBM) vertical well) in the western Fukang mining area in the southern margin of the Junggar Basin, Xinjiang, China is relatively high. However, there are significant differences between gas and water production of CBM wells at different locations in the area, and the reason has not been adequately explained. To explore the distribution characteristic of coalbed methane and water in the Fukang mining area, the three-phase CBM gas (adsorption gas, free gas, and water-soluble gas) content was determined based on theoretical analysis and simulation. Combining the calculation results and the basis of geological data, the CBM-water differential distribution in the study area was discussed. The results show that the average daily water production and average daily gas production of CBM wells show a negative correlation in the study area. The CBM wells with high daily gas production are mainly located in the high areas of the structure, and these wells commonly begin to produce gas within a short period. The calculation of three-phase CBM gas content and the test results of gas composition show that the gas content (especially the free gas) is relatively high in the high areas of the structure, while the concentration of CH is relatively low. Meanwhile, the concentration of CH shows a positive correlation with buried depth, which indicates that CBM migrates from the deep areas to the higher areas. The calculation of equivalent water level elevation and hydraulic head shows that the groundwater mainly flows from the central part to the east and the west within the CBM well areas, and the groundwater flows downward along the coal seam controlled by gravity, which results in the CBM-water differential distribution. The CBM-water differential distribution in the western Fukang mining area is the result of coupling control of tectonic and hydrological geology factors. Multistage tectonic movements formed large-scale folds and faults in the area, which controlled the migration direction of CBM and groundwater. The dip angle of the stratum in the study area is commonly greater than 45°, and the gravity effect is greater in the process of groundwater flow, which promotes the CBM-water differential distribution. Free gas migrates to the high area of the structure, and groundwater accumulates in the axial part of the syncline. The results in this study provide a basis for the large-dip angle CBM exploration and development in the Fukang mining area.
中国新疆准噶尔盆地南缘阜康矿区西部的单口井（煤层气垂直井）日产气量相对较高。然而，该区域不同位置煤层气井的产气与产水情况存在显著差异，其原因尚未得到充分解释。为探究阜康矿区煤层气与水的分布特征，基于理论分析与模拟确定了煤层气三相（吸附气、游离气和水溶气）含量。结合计算结果与地质资料依据，探讨了研究区煤层气与水的差异分布。结果表明，研究区内煤层气井的日均产水量与日均产气量呈负相关。日产气量高的煤层气井主要位于构造高部位，且这些井通常在短时间内开始产气。煤层气三相含量计算及气体成分测试结果表明，构造高部位的气含量（尤其是游离气）相对较高，而甲烷浓度相对较低。同时，甲烷浓度与埋藏深度呈正相关，这表明煤层气从深部向高处运移。等效水位标高与水头计算表明，煤层气井区内地下水主要由中部向东、西两侧流动，且地下水沿煤层在重力作用下向下流动，这导致了煤层气与水的差异分布。阜康矿区西部煤层气与水的差异分布是构造与水文地质因素耦合控制的结果。多期构造运动在该区域形成了大规模褶皱和断层，控制了煤层气和地下水的运移方向。研究区地层倾角通常大于45°，地下水流动过程中重力作用较大，促进了煤层气与水的差异分布。游离气向构造高部位运移，地下水则在向斜轴部聚集。本研究结果为阜康矿区大倾角煤层气勘探开发提供了依据。
