Abstract
Reservoir simulation traditionally involves prediction of fluid component and pressure profiles over time scales that are typical of oil and gas recovery processes. As commercial reservoir simulators evolve and become more sophisticated and accurate, they are increasingly being applied to marginal fields including reservoirs that have stress dependent problems.
Recently, efforts have been made towards coupling 3-D finite difference elastic stress solutions with fluid flow in a commercial reservoir simulator (SPE 65107, SPE 79697). In this paper the implementation of a finite element method to solve the rock elastoplastic stress equations that are coupled to reservoir fluid flow is introduced. This method has been chosen as an alternative to the finite difference method in order to produce higher accuracy in situations where the finite difference method has unacceptable errors. In addition, a non-isotropic work hardening plastic algorithm has been derived as part of this finite element implementation. Together they provide an improved analysis of weaker, tectonically stressed and faulted reservoirs. Geomechanical issues such as subsidence/compaction, wellbore failure, and the impact of stress-dependent flow parameters that affect fluid production can be modelled.
Advantages and disadvantages of computing the stress coupled to fluid flow by finite difference and finite element methods are discussed. An analysis of error in the two methods, larger scale coupled geomechanical reservoir simulation, solution of the equations and some future directions are included. A workflow is offered that takes into account data collection for the simulator, calibration and interpretation of results. This workflow is important because knowledge of reservoir engineering, reservoir simulation and geomechanical engineering are needed in order to produce a meaningful coupled geomechanical prediction.
