An advanced 3D continuum finite element model for field-scale in-situ stress simulation of rock media

Abstract

Accurate field-scale three-dimensional (3D) stress inversion using numerical simulation is crucial for obtaining in-situ stresses required for the safety and efficiency of underground minerals and energy resources extraction. However, existing commercial packages fall short in dealing with large-scale 3D stress inversion simulations and handling complex geological models containing faults and fractures. This work lays the foundation for the development of an optimised continuum Finite Element (FE) code (3DiStress) to simulate the 3D stress state in elastic media, capable of handling complex geological models. Such a computational framework employs advanced algorithms and state-of-the-art techniques, including the implementation of fault modelling through the effective medium theory, efficient large-scale model handling via vectorisation and sparse matrix storage, Superconvergent Patch Recovery (SPR) to calculate the stresses precisely, and iterative boundary conditions adjustment using Genetic Algorithm (GA) for stress inversion. For large-scale simulations, an effective solver, renowned for its robust handling of large sparse systems (Pardiso), is implemented to solve the resultant system of equations with high efficiency in parallel on a workstation and supercomputers. Furthermore, an iterative boundary condition adjustment is performed using GA, to calibrate the model against on-site stress measurements, thereby optimising the stress distribution. The principal advantages of this computational tool include its capability to accurately simulate complex faulted elastic media, flexible boundary condition optimisation, and the ability to easily adapt and integrate various algorithms, making it an asset for advanced geomechanical engineering applications.