Experimental Investigation of Coupled Geomechanical, Acoustic, and Permeability Characterization of Berea Sandstone Using a Novel True Triaxial Assembly

Abstract

Technological advancement of laboratory testing methods for investigating comprehensive geomechanical and transport properties of reservoir rocks is of great importance to the development of comprehensive geomechanical models that can improve operational risk assessment and production optimization. The in situ stress state can largely change due to drilling, completion, fracturing, and production, depending on the initial complexity of the geological setting, intrinsic rock anisotropy, and the degrees of artificial geomechanical and hydraulic disturbances. The versatility of a geomechanical model is therefore assured by reflecting the effects of stress magnitude and anisotropy on the considered properties. The purpose of this study was to investigate the effects of intermediate principal stress on the constitutive and flow behavior of Berea sandstone under true triaxial stress state. We present results of experiments with independent variation of intermediate principal stress under an array of octahedral normal and shear stresses, performed in dry and water-saturated cylindrical Berea sandstone core samples using a novel true triaxial testing apparatus. Data analysis indicated presence of microstructural behavior suggestive of opening and closing of microfractures, and revealed the effect of intermediate principal stress on deformation, wave velocities, and permeability. Vertical permeability displayed reduction to a smaller extent under increased vertical stress than under increased radial stress while exhibiting a steady decline under higher mean stress.