Hydraulic and chemical data collected along the eastern limb of the Alexander Creek Syncline near Weary Creek in southeastern British Columbia provide valuable insight to gas origin and reservoir character of the Jurassic-Cretaceous Mist Mountain Formation.
Carbon and hydrogen isotope data for formation water and methane gas collected from the Mist Mountain succession indicate on-going in-situ generation of methane and carbon dioxide through methanogenesis.
Single well recovery tests indicated that the permeability of the coal and sandstone beds ranges from approximately 1.5 to 60 mD. Hydraulic gradient and pumping test data for Site 1 indicate at least partial hydraulic connection between and among the beds.
Collectively, the data point toward a complex source and reservoir rock marked by variable physical characteristics which may impart different responses to depressurization and gas production.
Industry and government are currently assessing the coalseam gas (CSG) resources of the Western Canada Sedimentary Basin (WCSB). Coal basins lying within the Rocky Mountain Front Ranges of southeastern British Columbia are among potential areas for CSG development. The Elk Valley, and in particular, the area near Weary Creek is among the more promising (Fig. 1).
Exploration within the Weary Creek area has progressed from coal in the early 1970's to coalseam gas in the late 1980's and 1990's. The coal resource for the area has been investigated by numerous workers, however, a series of studies completed by ELCO Mining Ltd.(1) are among the most comprehensive.
CSG exploration in the immediate study area has been carried out by Norcen Energy Resources Ltd. The data compiled by Norcen have been assembled as part of a detailed review of CSG wells drilled in Canada. (2) Detailed accounts of the hydrogeology and hydrochemistry of the study area also have been compiled. (3, 4, 5)
The current work focuses on the Mist Mountain Formation within the Weary Creek exploration area. The study incorporates data from various sources. (1, 2, 3, 4, 5)
Detailed stratigraphy along the eastern limb of the syncline has been documented in coal exploration programs and feasibility studies. (1, 5,) Two sites, designated Site 1 (Fig. 2) and Site 2 (not shown), show a complex succession of interbedded mudstone, sandstone, siltstone and coal. Each site is instrumented with a pumping well and an array of monitoring wells completed at varying depths.
Groundwater samples collected from the monitoring wells, open wells, streams, seeps, and ponds within the valley were analyzed for routine groundwater chemistry and hydrogen and carbon isotopes (from dissolved gases). Single well response test data and long-term pumping test data collected from Site 1 were used to evaluate the hydraulic conductivity/permeability and the response of the Mist Mountain beds to depressurization.
Analyses of dissolved methane gas in groundwater sampled from monitoring wells at Site 1 and Site 2 and open exploration wells showed a δ13C range from -50 to - 60% and δ2H range from about -410 to -290%. The groundwater samples collected from selected monitoring wells at Site 1 and open exploration wells also showed high bicarbonate concentrations of up to 1800 mg/l (as dissolved inorganic carbon, DIC).
