AAPG Foundation 2019 Grants-in-Aid Projects

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Variation of rock mechanical properties in the sequence stratigraphic context of the Upper Devonian New Albany Shale, Illinois Basin


Rock mechanical properties of unconventional tight shale reservoirs are key parameters in shale oil/gas exploration and development. Understanding the stratigraphic variation of rock mechanical properties in black shale successions is critical for identifying target intervals for horizontal drilling and hydraulic stimulation. In this study, high-resolution hardness tests (5 cm spacing) using an Equotip Bambino 2 hardness tester and geochemical analyses (10 cm spacing) using a portable x-ray fluorescence analyzer will be conducted on a New Albany Shale core to study the stratigraphic variation of hardness and the control of rock composition on the hardness of this marine black shale. Petrographic characteristics of shales with high and low hardness values will be examined using a field emission scanning electron microscope. Biogenic silica content will be calculated by subtracting the Si associated with detrital Al from total Si. Hardness variation will be evaluated in the sequence stratigraphic context of the New Albany Shale, as well as related to mineral variability (silica, biogenic silica, calcite, dolomite, and clay minerals) and organic matter content. Our expected results are that the hardness of black shales is not controlled by total silica content, but by biogenic silica content because the latter forms an interconnecting rigid framework during diagenesis. We further expect that hardness is the highest at maximum flooding surfaces because that is where abundant biogenic silica is observed in the rock. Because most productive shales are marine kerogen type II sequences, findings of this study can be applicable to other oil and gas shale plays.