Modeling of 3D Crack Attributes and Crack Densities in Geothermal Reservoirs

Abstract

We describe a Matlab-based, interactive, self-contained, graphics-oriented code to process shear-wave splitting data from microearthquakes in order to image the fractured subsurface in geothermal reservoirs. The code consists of three main modules: 1) data processing, 2) forward modeling, and 3) inverse modeling. The first module allows for rapid and precise measurement of fast S-wave polarizations and split delay times through the display of seismic waveforms, corresponding power spectra, and particle motion plots. The second module uses the basic horizontal transverse isotropy (HTI) model to simulate crack-induced anisotropy and computes S-wave polarizations, time delays, and synthetic seismograms. One or two crack sets can be simulated. Equal-area projection diagrams of polarizations and time delays, as well as rose diagrams for specific crack models are interactively generated. The third module permits inversion for crack geometries through interactive trial-and-error comparison of real and synthetic data. The operator optimizes the fit while observing the sequence of previous trial-and-error events. A fully automated complementary inversion program is being incorporated. It discretizes the medium into blocks each having its own HTI model.