Abstract

The Lower Jurassic Gordondale Member is an organic-rich mudrock and is widely considered to have potential as a shale gas reservoir. Influences of Gordondale mudrock composition on total gas capacities (sorbed and free gas) have been determined to assess the shale gas resource potential of strata in the Peace River district, northeastern British Columbia. Sorbed gas capacities of moisture-equilibrated samples increase over a range of 0.5 to 12 weight percent total organic carbon content (TOC). Methane adsorption capacities range from 0.05 cc/g to over 2 cc/g in organic-rich zones (at 6 MPa and 30°C). Sorption capacities of mudrocks under dry conditions are greater than moisture equilibrated conditions due to water occupation of potential sorption sites. However, there is no consistent decrease of sorption capacity with increasing moisture as the relationship is masked by both the amount of organic matter and thermal maturation level. Clays also affect total gas capacities in as much as clay-rich mudrocks have high porosity which may be available for free gas. Gordondale samples enriched with carbonate (calcite and dolomite) typically have lower total porosities than carbonate-poor rocks and hence have lower potential free gas contents.

On a regional reservoir scale, a large proportion of the Gordondale total gas capacity is free gas storage (intergranular porosity), ranging from 0.1-22 Bcf/section (0.003-0.66 m³/section). Total gas-in-place capacity ranges from 1-31.4 Bcf/section (0.03-0.94 m³/section). The greatest potential for gas production is in the south of the study area (93-P) due to higher thermal maturity, TOC enrichment, higher reservoir pressure, greater unit thickness and improved fracture-potential.