Mechanical Upscaling in Highly Heterogeneous Rock Masses: Impact on Anisotropy and Subsurface Stress Prediction in the Bone Spring and Wolfcamp Formations of the Delaware Basin, USA

Abstract

ABSTRACT: The unconventional Bone Spring and Wolfcamp Formations are the development focus in the Delaware Basin. However, the high heterogeneity of the reservoir rocks challenges the selection of landing zones and increases the uncertainty of well performance. Estimating faithful elastic properties and predicting stress profiles along the wellbores are key to improve production and stimulation design. We acquire over 3,000 feet of continuous cores from five wells in New Mexico, Delaware Basin. We combine a variety of high-resolution, whole core-based characterization techniques that include hyperspectral and dual energy computed tomography imaging, ultrasonic velocities, and scratch index profiling, to quantify intrinsic, fine-scale variability in vertical transversely isotropic elastic properties indicating Young's modulus and Poisson's ratio perpendicular and parallel to bedding. Geomechanical averaging of this thinly bedded medium is then upscaled to a petro-mechanical facies scale for geological modeling and stress prediction. Elastic anisotropy as an emergent property of the upscaling process is contrasted with the anisotropy determined from the traditional core-plug based approach. Implications for stress profile prediction are discussed. 1. INTRODUCTION The Permian Basin of west Texas and southeast New Mexico constitutes the largest oil reserve and the highest producing oil field in the United States. The component Delaware Basin to the west incorporates significant development in the Bone Spring and Wolfcamp Formations. The Bone Spring Formation represents a mixed siliciclastic-carbonate succession deposited as sediment gravity flows under cyclical sea level fluctuations (Montgomery, 1997; Blake, 2020). Due to the cyclic sedimentation associated with changing sea level, the Bone Spring Formation can be subdivided into 1st, 2nd, and 3rd Bone Spring carbonates followed by sand units. The underlying Wolfcamp Formation records deepwater deposition of organic-rich mudstones interbedded with calcareous mudstones, calcareous siltstones, carbonates, and argillaceous mudstones that were deposited within mixed carbonate-siliciclastic fan systems (Yeap, 2021). In general, the Wolfcamp Formation can further be separated into A, B, C, and D units (Gaswirth, 2017). Both formations consist of mixed sediment gravity flow and suspension sedimentation deposits which often exhibit thin beds and facies resulting in high heterogeneity (Bievenour and Sonnenberg, 2019). Thin bed analysis is critical for reservoir property characterization but can be challenging when heterogeneity regularly exists at length scales below wireline log resolution (2 – 3 feet). Therefore, acquiring high-resolution measurements can significantly assist in identifying and quantifying thin-bed heterogeneity and properties assignment.