Geomechanical restoration as a tool for fractured reservoir characterization: Application to the Permian Basin, west Texas

We present a three-dimensional (3-D) geomechanical-restoration method as a reservoir characterization tool in the Permian Basin, west Texas. The Oates SW field produces gas from the Lower Devonian Thirtyone Formation within structural traps. The Thirtyone is a brittle chert with characteristics of a fractured reservoir: field development has experienced variable production trends for decades. To assess the impact of deformation on reservoir properties, we employ 3-D geomechanical restorations to model strain patterns associated with fault displacement and fold growth. We correlate these model strains with independent measures of natural rock strain to assess the viability of the restoration results. A semblance volume generated from 3-D seismic reflection data illuminates secondary faults and fracture zones that are not incorporated in the geomechanical restorations. Our analysis yields strong correlations between low semblance and elevated strain throughout the Thirtyone reservoir. These correlations indicate that restoration strains may be used to describe the distribution of secondary faults and fractures that are not represented in our models, providing predictive capabilities for defining fractured reservoir properties. We integrate strain and semblance with production data to evaluate these correlations at the borehole scale in the study area. We describe how tectonic strain likely enhanced permeability, directly impacting observed production trends. Our characterization of the Thirtyone reservoir demonstrates the ability to accurately predict strain distributions with geomechanical restorations where structure has been a significant factor in the development of reservoir permeability. We suggest that these methods show promise as a reservoir characterization tool for conventional and unconventional development operations.