Rock Physics Templates for Analysis of Brittleness Index, Mineralogy, and Porosity - A Barnett Shale Case Study

Rock brittleness plays a significant role in effective hydraulic fracturing for shale gas production, and is often related to mineralogy, mechanical properties, and microstructure features in shales. We construct a rock physics workflow to link elastic properties of shales to complex constituents and specific microstructure attributes. Multiple compositions and various pore geometries are considered using a self-consistent approximation (SCA) method. The laminated textures due to the preferred orientations of clay particles and possible laminated distribution of kerogen are considered using Backus averaging method to model the anisotropy of shales. Our rock physics model is calibrated on the well log data from the Barnett Shale, and is applied to generate rock physics templates for the interpretation and prediction of shale rock brittleness, mineral constituents, and porosity from elastic properties of shales. Results also show that the lamination of clay particles significantly reduces the sensitivity of shale elastic properties to porosity. Seismic AVO analysis based on the modeling data from top and bottom of the Barnett Shale formation illustrates that AVO intercept and gradient have predictable trends according to the variation of brittleness index, mineralogy, and porosity, which means that we can predict such characterizations from seismic responses.