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,distribu- tion 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 lo- cal gas content and the distribution characteristics of groundwater,the geological controlling mechanisms on gas distri- bution characteristics in different units were discussed. Results show that the main ions of produced water were Na+ , HCO- 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 identi- fied:The monocline-hydraulic sealing in the central of Malan was the richest area and the horst-hydraulic sealing in Dongqu was the richer area.