Laboratory constraints on the anisotropic dynamic-to-static ratios for shale's elastic constants: an example from the Duvernay unconventional reservoir

Abstract

Summary Dynamic material constants obtained by wave-based methods are different from their static counterparts. Constraining rock's elastic constants’ dynamic-to-static ratios (Rij) are important for understanding the geomechanical properties of earth's materials, particularly in the context of hydraulic fracturing that requires the knowledge of shale's static elastic constants. Conducting experiments with dynamic and elastic constants’ anisotropy, on top of their pressure dependency, properly accounted for is challenging. Here, we measure suites of dynamic and static elastic constants, with anisotropy fully accounted for, on the shale samples extracted from the Duvernay unconventional reservoir; a comprehensive set of geochemical/petrophysical measurements are obtained too. We observe that the dynamic-to-static ratios are generally not sensitive to the increasing pressures at σ > 50 MPa; we do not find a correlation with the samples’ mineral contents either. However, we find that Rij strongly correlates to the dynamic elastic constants except for the R11. The correlation between Rij, particularly Ri3, and the dynamic elastic constants can be explained by the sedimentary rocks’ compactness and the horizontal void spaces parallel to the rock's laminated bedding planes.