A Regional Diagenetic and Petrophysical Model for the Montney Formation, Western Canada Sedimentary Basin

Abstract

The Lower Triassic Montney Formation of the Western Canadian Sedimentary Basin is a world-class unconventional resource of gas, gas condensate and oil. Although commonly described as a shale, it is a siltstone over most of its subcrop, which presents complications for understanding and predicting petrophysical properties and hydrocarbon distribution. Petrophysical properties are functions of rock fabric, mineralogy and diagenetic processes, which in turn depend on sediment provenance, depositional environment, the pressure and temperature history, and fluid flow. In this study we are building a basin-wide petrophysical assessment of the Montney Formation, related to mineralogy and diagenesis and correlated with a sequence stratigraphic model. Datasets include mineralogical analyses from QEMSCAN and XRD, whole rock geochemical analyses by ICP-MS/ ICP-EAS, petrographic analysis from thin section investigation with optical and cathodoluminescence microscope and SEM imaging and pore system characterization. The Montney paragenetic sequence includes both pore-occluding and porosity-enhancing events. Pore-occluding events include precipitation of cements (quartz, feldspar, calcite and several generations of dolomite), mineral replacement (dolomite was found to replace silicate grains and gypsum replaces carbonates) and precipitation of authigenic phases in open pore space (pyrite and different types of clay). Pore-enhancing events include dissolution of different phases (feldspar, quartz and carbonate bioclaststic grains). Mapping mineralogy and diagenesis throughout the basin and incorporating this information together with well-logs into GAMLS software (Geologic Analysis via Maximum Likelihood System) enabled us to generate a lithological model of the Montney that was fine-tuned against core logs. From the calibrated model, we calculated porosity and water saturation profiles for selected wells and compared these results with porosity data obtained in the lab. This study is the first attempt at understanding pore systems of the Montney formation on a regional scale and within the sequence stratigraphic boundaries. Our results provide a platform for modeling basin scale fluid flow and predicting hydrocarbon distribution in the Montney.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015