Artificial thermal maturation of source rocks at different thermal maturity levels: Application to the Triassic Montney and Doig formations in the Western Canada Sedimentary Basin

Abstract

Artificial thermal maturation of petroleum source rocks is widely performed by either open- or closed-system pyrolysis. These experiments are performed usually on immature source rock or isolated kerogen samples to quantify petroleum generation potential and to calculate kinetic parameters. Here, we characterize a maturation series from the Triassic Montney and Doig formations in the Western Canada Sedimentary Basin (WCSB), in order to investigate the evolution of the source rock properties and their corresponding kerogen kinetic parameters as a function of the thermal maturity. Organic petrography determined the thermal maturity and the spatial distribution of organic matter particles. Rock-Eval Shale Play analyses were then applied to assess the presence of both free and sorbed hydrocarbons still contained in the sample as well as the hydrocarbon generation potential. Based on vitrinite reflectance values, three kerogen samples from the Doig Formation and one kerogen sample from the Montney Formation at different thermal maturity levels were selected for analysis of bulk kinetic parameters (e.g., activation energy distribution, frequency factor) using programmed open-system pyrolysis. Additionally, we evaluated the type of hydrocarbons and determined the molecular composition of organic compounds that comprise the first two Rock-Eval peaks (Sh0 and Sh1) obtained during the improved thermovaporization. TD–GC–MS–FID analyses were carried out on rock samples sequentially from 100°C to 200°C and then from 200°C to 350°C in order to characterize the composition of hydrocarbons represented by each Rock-Eval Shale Play peak. Free and sorbed low-to-medium molecular weight aliphatic and aromatic hydrocarbons (<C20) are the main hydrocarbon components released in the temperature range corresponding to the Rock-Eval Shale Play Sh0 parameter. Medium and high-molecular weight hydrocarbons (C10–C30 aromatics and saturates) are predominant components thermally released in the temperature range corresponding to the Rock-Eval Shale Play Sh1 parameter. Results show both an increasing activation energy and loss of petroleum generation potential as thermal degradation proceeds. The Shale Play method has been developed to better discriminate the generated fluids (Sh0+Sh1) from the residual kerogen (Sh2) providing a more accurate Rock-Eval Tmax. Sh0 and Sh1 parameters also offer a practical way for an early estimate of oil in place.