Characterizing the Geomechanical Properties in Middle and Upper Devonian Horn River Shale, Northeast British Columbia, Canada

Abstract

Economic development of shale gas depends substantially on hydraulic fracturing, which can be optimized by proper characterization of geomechanical properties. Heterogeneity in shale composition results in great spatial and stratigraphic difference in geomechanical properties, which are typically described by Young's modulus and Poisson's ratios. We have analyzed the Middle and Upper Devonian Horn River Shale, including the Evie, Otter Park Members and the Muskwa Formation, which is a major shale gas target in Western Canada Sedimentary Basin. Core hardness measurements, Young's modulus, Poisson's ratio and brittleness calculated from dipole sonic and density log data, geochemical composition analysis, scanning electron microscopy (SEM) images with complementary EDS maps and SEM-CL (Cathodoluminescence) techniques were carried out on four long cores in order to characterize the variation in rock mechanical properties and relate them to rock composition. Clay content is the most significant factor controlling the brittleness of shale rocks, showing a strong negative correlation to hardness. The behavior of quartz, typically regarded as a brittle mineral, is more complex. Authigenic quartz is positively correlated to brittleness while the detrital quartz is negatively correlated. No correlation between hardness and TOC content was observed, although it is commonly regarded as a ductile material. Carbonate generally shows positive relationship with brittleness. Different lithofacies vary greatly in geomechanical properties. Massive mudstone and pyritic mudstone have highly brittle, while laminated and bioturbated mudstone have relatively ductile. SEM-CL images suggest that massive quartz cement significantly enhances brittleness by forming rigid framework in massive and pyritic mudstone. Less quartz cements were observed in the laminated and bioturbated mudstones because of the presence of clay minerals surrounding detrital quartz grains. The geomechanical properties display geographic and stratigraphic variation. Brittleness is higher in distal areas of the basin than in proximal areas where more clay minerals were trapped. The Otter Park member, a lowstand unit that is richer in clay minerals is more ductile than the underlying Evie Member and the overlying Muskwa Formation that were deposited during higher sea level and are more rich in carbonate and quartz, respectively.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016