Numerical and experimental simulations of multiarray azimuthal laterolog sonde responses in fractured reservoirs

Abstract

The occurrence, orientation, and development of fractures are key parameters in the evaluation of carbonate and volcanic reservoirs. We have used a 3D finite-element method to numerically simulate the logging responses of a newly proposed multiarray azimuthal laterolog sonde (MALS) in a fractured formation. More importantly, a physical simulation performed with a scaled-down 3D resistivity apparatus was developed to verify the numerical simulation results. Comparative analysis indicated that the laterolog resistivity curves are controlled by the fracture dip angles. High-angle fractures normally correspond to positive differences in the array laterolog curves, whereas fractures with low dip angles consistently result in a negative difference. The MALS tool also provides an azimuthal resistivity measurement that can be used to determine the fracture dipping direction. The sine-wave trend in the 2D imaging of azimuthal resistivity displays the fracture occurrence. In addition, MALS can be used to identify vertical fractures around a borehole within a certain distance. In addition, combined with laterolog data, the fracture occurrence and extension length can be evaluated.