Elastic anisotropy in deep carbonate reservoir

Plugs drilled in two perpendicular directions (horizontal and vertical) from a core extracted from a deep (about 10 kft) vertical well were used to study the effect of anisotropy on the elastic, strength, and deformational properties of a carbonate formation. The effect of anisotropy on the elastic moduli and strength was determined using three laboratory techniques: ultrasonic velocity measurements (dynamic method); stress-strain measurements (static method); and the scratch test method (STM), where two resistance forces (tangential and normal) acting on the cutter were recorded and theoretically related with the unconfined compressive strength (UCS). A triaxial frame equipped with ultrasonic transducers was used to obtain the static and dynamic elastic moduli. The total porosity and permeability were measured using helium permeameter/porosimeter as well as NMR. Direct UCS tests were performed at the end of this study. The P- and S-wave velocities were also measured during the deformational tests. The above-mentioned properties of these samples show very small variations versus the orientation of the plugs. In this respect, the samples appear approximately isotropic.