Hydrogeology of a coal-seam gas exploration area, southeastern British Columbia, Canada: Part 2. Modeling potential hydrogeological impacts associated with depressurizing

A three-dimensional, finite-element flow model was used to assess the hydro geological effects of depressurizing coalbeds lying in the Weary Creek expl oration block, Elk River valley, southeastern British Columbia, Canada. The simulation results permit, at an early stage, assessment of the environmen tal and economic implications of how the flow system may respond to depress urization. Estimated reservoir conditions for the coal-seam gas targets lying within t he Upper Jurassic-Lower Cretaceous Mist Mountain Formation indicate that th e coalbeds must be depressurized by up to 350 m to attain the critical gas desorption pressure. The simulations suggest that depressurizing has little effect on groundwater flux to the Elk River. Simulated water production fo r three depressurizing wells operating under steady-state, single-phase flo w for initial reservoir conditions of 13 and 16.5 cm(3)/g is 645 m(3)/d (4, 057 barrels/d) and 355 m(3)/d (2,233 barrels/d), respectively. Groundwaters collected from monitoring wells have relatively low salinity, ranging from about 250-1,300 mg/L. The groundwater is supersaturated with r espect to Ca-Mg-Fe carbonates (calcite, dolomite, and siderite) and Al-bear ing silicates, including kaolinite and illite. Dissolved trace-metal concen trations are low; only Fe, Cd, Cr, and Zn exceed Canadian water-quality gui delines for aquatic life. Groundwaters were devoid of the more soluble mono cyclic aromatic organic compounds, including benzene, toluene, ethylbenzene , and polycyclic aromatic compounds, including naphthalene.