Static and Dynamic Mechanical Properties of Rock at Elevated Temperature

Abstract

Knowledge of mechanical properties of subsurface at elevated temperature is crucial to understand a range of processes in the earth’s crust and in building geomechanical models to assist in operating geothermal systems, nuclear waste repository, CO2 sequestration and hydrocarbon extraction. Although there exists sufficient literature reporting measurement of static mechanical properties on a range of rock types at elevated temperature, reported values for ultrasonic velocities are extremely limited. This in turn presents a challenge for the dynamic-to-static conversion of mechanical properties, a pivotal step in building geomechanical model. This paper presents the results of a laboratory study utilizing Castlegate and Berea sandstone and mudstone samples from a producing US reservoir at 75C. A decrease in both P and S wave velocity with temperature is observed in a Berea sample. A decrease in static Young’s modulus is observed in mudstone samples from two clay-rich reservoir intervals with one of the reservoir intervals demonstrating significant static and dynamic anisotropy. Additionally, the samples from both intervals mimicked the response of Castlegate for dynamic mechanical properties under constant hydrostatic stress. This study is intended to provide better representative inputs for improving the accuracy of subsurface characterization and geomechanical models for aforementioned applications.