URTeC: 2206 Determining Static Elastic Anisotropy in Shales from Sidewall Cores: Impact on Stress Prediction and Hydraulic Fracture Modeling Brian Crawford* 1 , Yueming Liang 1 , Philippe Gaillot 2 , Kelvin Amalokwu 1 , Xianyun Wu 1 , Robert Valdez 1 1. ExxonMobil Upstream Research Company, 2. ExxonMobil Upstream Business Development Copyright 2020, Unconventional Resources Technology Conference (URTeC) DOI 10.15530/urtec-2020-2206 This paper was prepared for presentation at the Unconventional Resources Technology Conference held in Austin, Texas, USA, 20- 22 July 2020. The URTeC Technical Program Committee accepted this presentation on the basis of information contained in an abstract submitted by the author(s). The contents of this paper have not been reviewed by URTeC and URTeC does not warrant the accuracy, reliability, or timeliness of any information herein. All information is the responsibility of, and, is subject to corrections by the author(s). Any person or entity that relies on any information obtained from this paper does so at their own risk. The information herein does not necessarily reflect any position of URTeC. Any reproduction, distribution, or storage of any part of this paper by anyone other than the author without the written consent of URTeC is prohibited. Abstract To effectively predict the performance of unconventional wells it is essential to incorporate sufficient geologic complexity to allow for realistic variability in the mechanical properties and subsurface stresses controlling hydraulic fracture geometries and containment. To this end, the ability to derive static poroelastic anisotropy using only routinely acquired horizontal core plugs for geomechanics testing, as opposed to the more established practice requiring multiple orientated samples, offers considerable advantages: improved predictive accuracy associated with enhanced model inputs; increased measurement precision due to the elimination of between-sample variability; cost savings resulting from sidewall versus whole core sampling. Subsurface elastic anisotropy can vary significantly between formations associated with the amount and preferred orientation of clay minerals and the presence of organic-rich laminations, resulting in significant layer-to-layer fluctuations in horizontal stress magnitude due to local elastic strain accommodation. Assuming vertical transversely isotropic (VTI) symmetry, a novel experimental geomechanics technique and associated analytical solutions are described for deriving directional elastic properties using only horizontal core plugs as routinely collected for conventional characterization purposes. Quantitative mineralogy combined with established micromechanical theory is then utilized to determine an additional poroelastic anisotropy (non-unitary vertical and horizontal Biot’s coefficients) that can further improve subsurface stress prediction workflows, ideally implemented through cross-functional geoscience and engineering collaboration. An extensive database of core-derived VTI poroelastic material coefficients is used to demonstrate generic stiffness and compositional controls on the observed magnitude of anisotropic response. Example subsurface stress profiles determined via the conventional isotropic assumption versus the enhanced VTI realization are then compared to illustrate a first order impact on subsequent hydraulic fracture modeling outcomes. This technique is currently being applied by petrophysicists for correcting dynamic elastic properties determined from acoustic-logging of unconventional plays to equivalent anisotropic static values, as required by completions engineers for enhanced in situ stress prediction and hydraulic fracture modeling. In addition to geoscience and engineering collaboration towards improved well treatment design, anisotropic mechanical earth models have broader application, particularly for drilling-related wellbore stability issues and structural geological applications including top seal storage and integrity assessment.