西山煤田古交矿区煤层气藏水文地质特征及其控气作用

煤层气藏的水文地质条件是控制煤层气运移、散失、分布和富集的重要因素之一。以西山煤田古交矿区为研究对象,分析产出水离子浓度、水质水型、矿化度和煤层含气量分布特征,结合地下水动力场分布特征,划分区域水文地质单元,并讨论不同单元内含气量分布特征及地质控制机理。结果表明:(1)该区煤层气井产出水离子以Na~+,HCO_3~-为主,水型主要为NaHCO_3型,该区煤层气井产出水矿化度介于632~2 512 mg/L,属于淡水-微咸水;(2)根据折算水位和矿化度分布特征将矿区划分为补给径流区、滞留区以及过渡地带的弱径流区3种水文地质单元,滞留区含气量最高,弱径流区次之;(3)古交矿区煤层气的富集成藏受构造、水文地质条件双重控制,在屯兰中部形成单斜-水力封堵型煤层气藏,为全区煤层气最为富集区,东曲断层比较发育,形成地垒-水力封堵型煤层气藏,为煤层气较为富集区。

Hydrogeological characteristics of CBM reservoirs and their controlling effects in Gujiao Mining Area,Xishan Coalfield

Hydrogeological condition is one of the most important factors controlling the migration,dispersion,distribution and accumulation of coalbed methane (CBM) in coal reservoir.In this paper,the water produced from CBM wells in Gujiao mining area was monitored in terms of concentrations,water quality and salinity.Then,combined with the local gas content and the distribution characteristics of groundwater,the geological controlling mechanisms on gas distribution characteristics in different units were discussed.Results show that the main ions of produced water were Na+,HCO-3 and the type was NaHCO3.The total dissolved solids (TDS) of produced water were relatively lower,which ranged from 632 to 2 512 mg/L,belonging to freshwater-saline water.The research area were divided into runoff zone,weak runoff zone and stagnant zone,and the stagnant zone according to discounted water level and TDS.The stagnant zone had the highest gas content,while the gas content in the weak runoff zone was relatively lower.The enrichment of Gujiao mining area was controlled by structure and hydrogeological conditions.Now two hydraulic patterns were identified:The monocline-hydraulic sealing in the central of Malan was the richest area and the horst-hydraulic sealing in Dongqu was the richer area.