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

Eric Flodin¹ and Phillip G. Resor^2
1Energy Technology Company, Chevron, San Ramon, CA
²Earth and Environmental Sciences, Wesleyan University, Middletown, CT

The stratal geometry of the Permian Capitan Reef Complex has been influenced by syn-sedimentary deformation including tilting, folding, fracturing, 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.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas