Shale Gas Potential in Lower Cretaceous Strata of Northeastern British Columbia, Canada

Gareth Chalmers and R. Marc Bustin
University of British Columbia, Vancouver, BC

The Lower Cretaceous Moosebar and Buckinghorse Formations are thick sequences of organic-rich shale in northeastern British Columbia and are potential gas shale resources. To assess the gas potential, the quality (type and maturity) and concentration of organic matter, sorption capacity and porosity have been determined.

The TOC ranges between 0.42 and 14.48% and averages 2.34%. Methane adsorption capacities vary from 0.05 to 1.15 cc/g (1.6 to 37 SCF/ton) at a pressure of 6 MPa (870 PSI) and a temperature of 30°C. Porosity ranges between 1.5 and 22.5% with an average of 6.9%. The total gas capacity is the addition of free gas to the sorbed gas calculation. The total gas capacity is between 3.3 cc/g (106 Scf/ton) and 11.7 cc/g (376 Scf/ton). As the average stratal thickness is 105 metres, the total gas in place is up to 66 Bcf/section.

A strong positive correlation exists between the TOC content of the shale and its capacity to store methane. Other factors such as the moisture content become more important in the TOC-lean samples. Rock-Eval analysis and organic petrology show that samples with a high TOC are dominated by terrestrial derived Type-III and IV organic matter that are sourced from the coastal areas to the south of the study area. Inertodetrinite appears to be a significant contributor to the organic-rich shales that are proximal to the shoreline. Higher gas potential is found in the samples that contain higher contents of inertodetrinite.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005