AAPG Annual Convention and Exhibition

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Predicting Fracture Orientations and Distributions Through Elastic Dislocation Theory and Coulomb Stress Changes


Analysis of 3D models using Elastic dislocation theory and Coulomb stress allows the impact of fractures on conventional or unconventional hydrocarbon resources to be better understood. We use the new Fault Response Modelling tool within Move” which allows for lateral variations of rock properties and considers the effects of pore pressure and fault-induced stress changes to more accurately reproduce natural fracture systems. The Fault Response Modelling workflow involves using elastic dislocation theory to calculate displacements, strain and stresses following slip on joints or faults. The stresses induced by faulting can then be added to the regional stress field, or used in isolation, to calculate Coulomb stress changes on possible fractures in the surrounding rock. The tool also allows users to calculate Coulomb stress associated with any restoration or modelling operation that has been carried out in Move, providing the user with greater flexibility and allowing different deformational mechanisms and geological processes to be isolated and quantified. Within the new tool, these calculations can be used to determine the optimal fracture orientations by searching through all possible fractures and slip directions to maximize the Coulomb stress. The benefits of this new workflow and its ability to more realistically predict fracture orientations and distributions will be demonstrated with cases studies from the La Concepción oil field in the Maracaibo basin of Venezuela and the Sant Corneli anticline in northern Spain. In the former case study, fault-related fractures predicted using the Fault Response Modelling tools will be compared to well data; pore pressure changes associated with fault activity will also be modelled and incorporated into the fracture prediction. For the second case study, optimal fracture orientations based on stresses calculated following kinematic and geomechanical restorations, and from outputs from the Fault Response Modelling tool will be examined.