Characterization of Organic Matter in the Canadian Lower Triassic Montney Shale Gas Reservoir

Sanei, Hamed; Freeman, Melissa; Clarkson, Chris; Gentzis, Thomas

The Lower Triassic Montney Formation is currently a prolific gas producer in the Western Canadian Sedimentary Basin and is projected to continue as a major energy resource in the future. However, the Montney Formation is notoriously difficult to characterize and model using conventional methodology due to the presence of heterogeneities below the scale of traditional analysis. This study applies innovative methodology to investigate the vertical heterogeneity of reservoir quality and the influence of organic matter (OM) on pore structure and connectivity. This was conducted using profile permeability, organic petrography, and a slow heating Rock-Eval pyrolysis. Manual integration of Rock-Eval pyrograms over extended temperature range shows traditional S2 peaks can be quantitatively divided into three components based on their degree of de-volatilization including light oil, heavy oil, and the most refractory thermally degraded bitumen. The results show that the bulk of hydrocarbon in the study samples consists of the refractory OM component attributed to thermally degraded bitumen. Optical petrography revealed the lack of significant indigenous kerogens, instead confirming an interconnected, intergranular network of degraded bitumen mats throughout the samples. The pervasive nature of the degraded bitumen is indicative of hydrocarbon migration into the formation, followed by extensive thermal degradation. There is an inverse relationship between the profile permeability and distribution of refractory hydrocarbon suggesting that the degraded bitumen may obstruct porosity and hence hinders fluid flow. This is in contrast to the increase to porosity and permeability experienced from the organic matter in many unconventional reservoirs.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013