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Lower Cretaceous gas shales in northeastern British Columbia, Part II: evaluation of regional potential gas resources

Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada

R. Marc Bustin

Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada

The Lower Cretaceous Buckinghorse Formation and equivalent strata in northeastern British Columbia are investigated for potential as gas shale reservoirs. A total of 215 cored samples were analyzed for methane sorption capacity, moisture content and total porosity. Organic geochemistry was determined by Rock-Eval 6 ® analyses and a suite of samples with a variation in TOC content, mineralogy and porosity were analyzed for permeability. Total organic carbon (TOC) contents vary between 0.2 and 16.99 wt%, with an average of 2.52 wt%. Organic matter is a mixture of Type I, II and III kerogens. Moisture contents vary between 1.5 and 11 wt%, with an average of 4.6 wt%. Methane sorption capacities range between 0.03 and 1.86 cm³/g, with an average of 0.53 cm³/g at hydrostatic pressure. Porosity of the shale is between 0.7 and 16% and averages 6.5%. The total gas capacity is between 1.49 and 14.5 cm³/g with an average of 5.7 cm³/g at hydrostatic pressure.

The highest level of thermal maturity, as defined by Rock-Eval T_max, occurs along the deformation front where depths of burial were the greatest. T_max values ranged between 416°C (immature) and 476°C (overmature). TOC content and reservoir pressure are the primary controls on the methane sorption capacity of the strata. The highest methane sorption capacity is in NTS map section 94-P of the study area near the British Columbia, Alberta and Northwest Territory borders, where TOC contents are the highest and the kerogen is dominated by types I and II. Areas with greater depths of burial (adjacent to the deformation front) have higher reservoir pressures and this increases the ability to store significant amounts of sorbed gas even though TOC is lower than the shallower sediments. The TOC is lowest along the deformation front likely because of higher sedimentation rates and higher thermal maturities compared to the distal parts of the basin.