沁水盆地安泽区块煤层气藏水文地质特征及其控气作用

Hydrogeological characteristics of CBM reservoirs and their controlling effects in Block Anze,Qinshui Basin

在我国华北地区,煤层气藏的水文地质条件与煤层气的运移、散失、保存、富集等关系密切,但过去很少有学者采取动态监测地下水特征的方式来分析其对煤层气藏的影响。为此,以山西沁水盆地安泽区块煤层气藏为研究对象,在动态监测煤层气产出水离子浓度、水质水型及矿化度变化的基础上,结合该区煤层气井开发实际与地下水动力场分布特征,讨论了不同水文地质单元的产气、产水情况,并利用微量元素检测结果分析了合层排采的井间干扰。最后,结合构造、煤质特征探讨了水文地质条件对煤层气富集与产出的控制作用。结果表明:①该区主力煤层为下二叠统山西组3号煤和上石炭统太原组15号煤,煤层顶底板大部分为砂岩和泥质砂岩:②煤层气产出水离子浓度和矿化度随排采时间的增加不断降低,水型以NaCl型和NaHCO_3型为主;③将该区划分为弱径流区、径流区和滞流区3个水文地质单元,其中径流区产气量最高,滞流区产气量最低,合层排采井受15号煤的干扰较大。结论认为:该区煤层气的富集主要受断层及水动力条件的控制,下一步应加大对煤层气优势富集区的开发力度。

In North China, coalbed methane （CBM） reservoirs are hydrogeologically related with the CBM gas migration, dispersion, preservation and enrichment, but groundwater dynamic monitoring technology was seldom used to analyze the effects of hydrogeological conditions on CBM reservoirs. In this paper, the water produced from CBM reservoirs in Block Anze, Qinshui Basin, was monitored in terms of ion concentration, water quality and salinity. Then, combined with the actual production data of CBM wells and the hydrodynam- ic field distribution characteristics of the groundwater, gas and water production rates of different hydrogeological units were discussed. Well interference during commingled production was also analyzed by use of trace element test results. And finally, the controlling effects of hydrogeological conditions on CBM enrichment and production were probed in terms of reservoir structures and coal characteristics. Results show that the major coalbeds are No.3 coalbed of the Lower Permian Shanxi Fm and No.15 coalbed of the Upper Carboniferous Taiyuan Fro, with their roofs and bases mostly composed of sandstones and argillaceous sandstones. The water produced is mainly of NaCI and NaHCO3 types and its ion concentration and salinity drop continuously with the proceeding of the production. This area is di- vided into three hydrogeological units, i.e. weak runoff zone, runoff zone and retaining zone. In particular, the runoff zone provides the highest gas production, while the retaining zone reveals the lowest. Commingled producing wells are mainly interfered by No.15 coal- bed. It is concluded that CBM enrichment in this area is mainly controlled by faults and hydrodynamic conditions. So it is necessary to strengthen the development of CBM dominant enrichment zones.