The Petrophysical and Mechanical Properties of Oklahoma's Crystalline Basement

From 2009 to 2016, a drastic increase in seismic activity occurred in the Central and Eastern US (CEUS), and particularly in the Oklahoma-Kansas region. The majority of hypocenters have been traced to the crystalline basement rock. Forecasting future seismic hazard and predicting the in-situ response of such terranes requires their geomechanical parameters be adequately constrained. This work assesses the mechanical and petrophysical properties of several sets of basement rocks from Oklahoma to provide a better framework for understanding intraplate seismicity and overall basement deformation. Laboratory experiments were conducted with granite and diabase basement rock samples. Evolution of compressional and shear wave velocity with increasing confining pressure was measured through a series of ultrasonic velocity tests. A suite of uniaxial and triaxial tests were conducted to measure the elastic and inelastic deformation behavior of the basement under both dry and water-saturated conditions. Deformation data was evaluated using the Mohr-Coulomb criterion and compared with additional pre-existing deformation data of igneous rock terranes. Results suggest a strong mechanical contrast exists between basement component rocks. Fluid-weakening in deformation tests indicates chemo-mechanical processes may also contribute to subsurface deformation in Oklahoma.