Dynamic Stress Mapping Utilizing Ultrasonic Tomography

ABSTRACT: Two indentation experiments were conducted to generate acoustic tomographic velocity imaging of a dynamically developing complex stress field. The indentation tests were conducted on dry Berea sandstone cores with successive loading increments up to 110 MPa being applied to a hardened steel indenter. A series of 20 acoustic sensors were arranged either in vertical or horizontal planes to tomographically image cross-sectional planes parallel and perpendicular to the indentation direction. The indentation generates a strongly heterogeneous stress field with the highest stresses located in the rock directly beneath the indenter. The regions of high stresses, delineated by an ABAQUS finite element solution, correspond to the tomographically mapped regions of high velocity. These results suggest that tomographic acoustic velocity changes resulting from perturbations in elastic stress states can be successfully mapped in porous reservoir rocks both in laboratory tests and in the field environment.