潞安矿区煤层气井产出水地球化学特征及意义

Geochemical characteristics and significance of water produced by coalbed methane wells in Lu’an Mining Area

水文地球化学分析是研究煤层气富集条件及开采动力条件的重要方法。以沁水盆地中南段潞安矿区山西组3号煤煤层气井产出水为研究对象,开展了矿化度、H/O稳定同位素和主要离子浓度分布特征研究,结合区域构造展布特征及煤层气开发历史分析了区内煤层气开发优选区。结果表明:(1)潞安矿区分布有3个高矿化度区(五阳井田、余吾西南部、高河北部–古城井田),地下水平均矿化度2000~3200 mg/L;1个低矿化度区域(常村井田和余吾井田中东部),地下水平均矿化度1500 mg/L。(2)煤层产出水中的δD和δ^(18)O值均落在该区大气降水线附近,表明该区各含水层均有来自大气降水的补给,且煤层中的水主要来源于大气降水。(3)潞安矿区地表水从东部太行山裸露岩层区向下运移至含煤地层和下部奥陶系含水层,而后在灰岩系中向东出露地表,补给辛安泉域。研究区内两条区域断层文王山断层和二岗山断层是开放性导水断层,为地下水运移提供了通道,其展布特征决定了地下水的基本流动规律,其控制区域内的煤层气含量较低;地下水在挤压性断层中华–安昌断层附近、天仓向斜和许村向斜轴部相对滞流,矿化度较高,是煤层气富集区,也是潞安矿区煤层气开发的优选区。

Hydro-geochemistry analysis is an important method for CBM exploration and development research.In this paper,the distribution characteristics of salinity,H/O stable isotope and ion concentration in sample water was investigated,and the optimal CBM development area was analyzed by the characteristics of regional structural distribution and the CBM development history.The testing water was from the No.3 CBM well of the Shanxi Formation Permian system in the Lu’an Mining area in the south-central part of Qinshui Basin.The results show that there are three high salinity areas in the mining area,with an average groundwater salinity of 2000-3200 mg/L,including Wuyang Minefield,southwestern Yuwu,and northern Gaohe-Gucheng Minefield.And there is a low salinity area in Changcun minefield and east-central Yuwu Minefield,with an average groundwater salinity of about 1500 mg/L.The δDand δ^(18)O of testing water are close to the atmospheric precipitation line in the research area,indicating that all aquifers are supplied by atmospheric precipitation,and the water in the coal seam mainly comes from atmospheric precipitation.It also shows that the surface water in Lu’an Mining Area moves downward from the exposed rock stratum of Taihang Mountain in the east to the coal-bearing stratum and the lower Ordovician aquifer,and then exposes eastward in the limestone series to supply the Xin’an spring area.The Wenwangshan Fault and Ergangshan Fault are open water-conducting faults,providing channels for groundwater migration.Their distribution characteristics determine the basic flow law of groundwater,with lower gas content in the area.There are three groundwater retention areas with higher salinity,including Zhonghua-Anchang fault,Tiancang syncline and Xucun syncline.They are not only gas enrichment areas,but also preferred areas for CBM development.