--> Application of Computed Tomography and Scanning Electron Microscopy in the Determination of Pore-Space Characterization of a Potential Unconventional Reservoir: A Case Study in Mowry Shale in the Powder River Basin, WY

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Application of Computed Tomography and Scanning Electron Microscopy in the Determination of Pore-Space Characterization of a Potential Unconventional Reservoir: A Case Study in Mowry Shale in the Powder River Basin, WY

Abstract

The Cretaceous Mowry Shale in the Powder River Basin (PRB), WY is a well-known hydrocarbon source for overlying Frontier and underlying Muddy sandstones. Recent studies have focused on the hydrocarbon potential of the Mowry formation as an unconventional reservoir. It consists of primarily siliceous black shale which can be subdivided into three intervals: a fissile, weakly cemented, bioturbated shale at the bottom; highly siliceous, thinly laminated, organic-matter-enriched shale in the middle; and a coarsening upward, bioturbated silty-shale in the upper section. Twelve primary bentonite beds are distributed throughout the Mowry section and can be correlated across the PRB. Investigation of cores, drill stem test, production data, rock evaluation and sequence stratigraphy indicates two ideal drill intervals within the middle Mowry section. The lateral continuity of these two zones and the correlation between bentonites provide further work on the facies changes and deformational structures across the PRB to find ideal drill locations. In this study, we utilize computed tomography (CT) and scanning electron microscope (SEM) to better understand the heterogeneity of pore space and fracture networks at varying depths in the PRB. CT and SEM analysis of available core samples within the potential drilling intervals provide critical information about micron-to-nanometer scale characteristics of the Mowry shale. A detailed fracture analysis yields a structural model to explain the potential tectonic effects on pore space evolution. Sampling across facies changes within the drilling interval will help develop an understanding of the effect that variations in depositional minerals or material have on pore space. The results of this study will show changes in granular and organic-matter-hosted pore space, pore throat size and effective permeability due to both structural deformation and variations in sedimentation. The major contribution of this study is to provide a better understanding for successful drilling practices in unconventional black shale and clay rich hydrocarbon resources.