Multiple Scenarios From Diverse Thermal Indicators: Contrasting Organic Versus Mineral-Based Methods for a Frontier Intracratonic Basin in the Canadian Arctic.

Abstract

The burial and thermal histories are critical elements in the evaluation of conventional and unconventional petroleum systems. For years, thermal parameters obtained through Rock-Eval and organic petrography have been the preferred approaches to understand the thermal evolution of basins. Various mineral-based methods have also been developed and increasingly applied to comprehend the thermal history of sedimentary successions. The Paleozoic Hudson Bay Basin in the Canadian Arctic is a large intracratonic basin and after an initial exploration phase (5 wells) in the 1970-1980 period, it was abandoned as based on Rock Eval 2 data, source rocks were deemed immature. However, all wells had gas kicks and bitumen-rich intervals. A research project by the Geological Survey of Canada aims at re-evaluating the petroleum systems of this basin with a particular attention to understanding its burial-thermal history. The burial-thermal research focusses on the Upper Ordovician stratigraphic interval at the base of the 2500 m preserved succession. Organic matter-rich source rocks and porous potential reservoir units (reef and hydrothermal breccia) occur over a short stratigraphic interval. These are particularly well exposed on Southampton Island at the northern reach of the basin where satellite and airborne radar images have identified nearby potential seawater oil slicks and hydrographic surveys have mapped seafloor pockmarks. The Upper Ordovician Type I-IIs shales are rich in TOC (up to 35%), with high HI value (average 630 mg HC/g TOC). New organic-matter based thermal indicators from Rock-Eval 6 and reflectance petrography indicate that the outcropping Upper Ordovician shales are immature (Tmax below 435°C and average Rvit-eq of 0.44%). Inverse modeling of apatite fission tracks data from basal Upper Ordovician sandstone suggest that the succession reach the early oil window with an acceptable temperature envelope of 65 to 85°C and best fit data of 72°C. Thermal evolution from fluid inclusions microthermometry data in early and late carbonate cements from porous Upper Ordovician reefs has identified an early hydrothermal event (Th of 120°C) and late burial oil window conditions (Th of 93°C); clumped isotope temperature data from these cements are currently being acquired. Therefore, assuming proper analytical techniques, various organic and mineral-based thermal analyses could yield significantly different results.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018