Organic matter characterization in mixed hydrocarbon producing areas within the Duvernay Formation, Western Canada Sedimentary Basin, Alberta

This paper characterizes organic matter in the mixed hydrocarbon (oil-dry gas, oil-condensate) producing areas of the Late Devonian Duvernay Formation in Alberta (Canada) by high-resolution RockEval data (n = 246) and petrography (n = 35) at three drillhole locations (Locations A and C distal, Location B proximal to Leduc Reef, respectively). Total organic carbon (TOC) ranges from 0.15-622 wt.% at Location A, 0.43-820 wt.% at Location B, and 1.84-5.23 wt.% at Location C with an overall median value of 3.42 wt.%. S2 values range from 0.20-7.42 mg HC/g of rock at Location A, 022-4.23 mg HC/g of rock at Location B, and 1.68-5.04 mg HC/g of rock at Location C. These results for samples from Locations A, B and C indicate that kerogen is Type I to Type II. The hydrogen index (HI) of these rocks is significantly lower (<160 mg HC/g TOC) than that of traditional oil-producing source rocks of this age (similar to 400-700 mg HC/g TOC). At Locations A and C, T-max lies within the oil window with a mean value of 459 degrees C; at Location B, T-max varies greatly between 434 and 488 degrees C, between the oil and gas window, with no observable association with sample depth. Vitrinite reflectance of samples ranges from 0.99-1.32%. T-max values do not correlate with vitrinite reflectance of the samples (R-2 = 0.04), nor with depth (R-2 = 0.4), suggesting that T-max is not a reliable indicator of thermal maturity in this system. Low TOC/S2, high mineral carbon is associated with intervals of intergrown sparry calcite and pyrite in petrographic samples at Location B. Organic matter within the Duvernay Formation was characterized as almost entirely solid bitumens, with very minor inertinite, <1% by volume). The RockEval and petrographic observations suggest that secondary diagenetic effects are the cause for the mixed hydrocarbon signature, rather than any spatial variation in depositional environment or thermal maturation regimes. (C) 2016 Elsevier B.V. All rights reserved.