Organic Matter Characterization of the Lower Cretaceous Garbutt Formation, Liard Basin, Canada
Recent exploration for unconventional hydrocarbon resources in British Columbia with abundant shale intervals leads to increase British Columbia's natural gas resources. However, higher economic value of gas condensates attracts higher attention to the formations in the gas condensate zone. The present study reports the high resolution organic matter characterization of subsurface samples of the Lower Cretaceous Garbutt Formation obtained from 3 cores in the eastern part of Liard Basin. The Garbutt Formation consists of black, silty shale and mudrock. Samples are from 3 wells in a north to south direction parallel to the eastern margin of Liard Basin in the vicinity of Bovie fault, at depths ranging from 1200 to 1400m. High percentage of farmboidal pyrite (Up to 30%), high Mo and U concentration of Garbutt Formation in two upper wells indicate a euxinic environment during deposition. The majority of samples have very good to excellent TOC content ranging from 1.1 to 10.3% with an average of 4.3%. The current TOC content of samples represents 75–88% of the residual carbon with an increasing trend from north to south. The Tmax values obtained from the Rock-Eval analysis ranges from 432 to 470°C which represent the onset of the oil window to the onset of the dry gas window toward south. Samples in the oil window with high S2 values exude oil under fluorescent light. The maceral group composition of these samples appears to reflect the thermal maturity populations. Those samples in the lowest maturity zone are predominately liptinite group macerals (alginate) (64%), with 25% vitrinite and 11% inertinite group macerals by volume. Samples within the middle population of maturity contain 44% liptinite group macerals (alginate), with higher vitrinite at (40%), and low inertinite (16%). Samples with the highest maturity, are rich in vitrinite (41%) and inertinite group (37.5%) macerals, and lower in liptinite group macerals (liptodetrinite) at 21.5%. Vitrinite reflectance (VRo) was measured in these samples and exhibit a slight variation in thermal maturity compared to Tmax values. Samples with lower maturity show two distinct vitrinite populations, one with an average peak of 0.75%, the other with an average peak of 1.08%. Within samples with higher maturity, these two populations are far closer, with greatly overlapping measurement distribution, with peaks at 1.49%, and 1.31%, respectively.
AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015