Integrating Geomechanical modeling and Three-dimensional Mapping to Constrain Deformation Associated with Growth of the Permian Capitan Reef Complex

Phillip G. Resor, Wesleyan University
Eric Flodin, Chevron Energy Technology Company

Abstract

The stratal geometry of the Permian Capitan Reef Complex has been influenced by syn-sedimentary deformation including tilting, folding, Previous HitfracturingTop, and faulting of strata. The importance of these effects has been a topic of debate for decades and impacts our understanding of the initial sedimentary geometry as well as the distribution of early-formed fracture systems. We use geomechanical finite element modeling to predict the magnitude and distribution of syn-sedimentary deformation associated with a prograding shelf margin. The model is linear elastic with heterogeneous layering comprised of four principal facies (platform, reef, upper slope, and lower slope/basin). In order to simulate reef growth, models are run step-wise where the outer geometry is replicated with each successive step. For each model run, the progradation-aggradation ratio is held fixed. Model results include basinward tilting of platform strata near the shelf edge due to differential compaction (fall-in geometry) and broad areas of high tensile stress in the platform and buried reef strata that would likely lead to tensile failure or extensional faulting. This post-depositional model geometry and pattern of strain concentration is similar to present-day stratal geometries and patterns of faulting revealed through three-dimensional mapping of high frequency sequence geometry in the Guadalupe Mountains. Interestingly, the model results are relatively insensitive to variations in basin sediment compressibility (Poisson’s ratio). However, increasing the progradation-aggradation ratio leads to higher tensile stresses and greater localization of tilting near the shelf margin, a result comparable to field observations in the Permian Capitan Reef Complex.