A rock physics model for estimating elastic properties of upper Ordovician-lower Silurian mudrocks in the Sichuan Basin, China

Abstract The elastic properties of shale and mudstone from unconventional subsurface reservoirs are of great significance for the evaluation of rock fracturing, especially for hydraulic fracturing and borehole stability. In this study, mineral compositions of the rock cuttings over 100 m in length from the well XK-1 (Wufeng and Longmaxi Formations in the Sichuan Basin, China) were accurately measured by automated mineralogy and a new multi-mineral equal probability contact Hertz-Mindlin model that considers three or more granular medium contacts is proposed to estimate the elastic properties of the Wufeng and Longmaxi Formations. The results show that elastic parameters obtained from the new multi-mineral equal probability contact Hertz-Mindlin model are consistent with those from sonic logging. Thus, this model can be used to estimate the elastic properties of Wufeng and Longmaxi shales. When applied to mudstone and sandy mudstone of Longmaxi Formation, the clay content plays an important role to improve estimates of the elastic parameters. The new rock physics model is fast, cost-effective, and provides an alternative in case there are no rock blocks available for conventional uniaxial or triaxial tests in the laboratory, or wireline logging tools are not best options.