Summary
This paper compares three techniques for coupling multiphase porous flow and geomechanics. Sample simulations are presented to highlight the similarities and differences in the techniques. One technique uses an explicit algorithm to couple porous flow and displacements in which flow calculations are performed every timestep and displacements are calculated only during selected timesteps. A second technique uses an iteratively coupled algorithm in which flow calculations and displacement calculations are performed sequentially for the nonlinear iterations during each timestep. The third technique uses a fully coupled approach in which the program's linear solver must solve simultaneously for fluid flow variables and displacement variables. The techniques for coupling porous flow with displacements are described and comparison problems are presented for single-phase and three-phase flow problems involving poroelastic deformations. All problems in this paper are described in detail, so the results presented here may be used for comparison with other geomechanical/porous-flow simulators.
Introduction
Many applications in the petroleum industry require both an understanding of the porous flow of reservoir fluids and an understanding of reservoir stresses and displacements. Examples of such processes include subsidence, compaction drive, wellbore stability, sand production, cavity generation, high-pressure breakdown, well surging, thermal fracturing, fault activation, and reservoir failure involving pore collapse or solids disposal. It would be useful to compare porous flow/geomechanics techniques for all of these processes, because some of these processes involve a stronger coupling between porous flow and geomechanics than others. However, this paper looks at a subset of these processes and compares three coupling techniques for problems involving subsidence and compaction drive. All of the sample problems presented in this paper assume that the reservoir absolute permeabilities are constant during a run. Displacements influence fluid flow through the calculation of pore volumes, and fluid pressures enter the displacement calculations through the poroelastic constitutive equations.
Several authors have presented formulations for modeling poroelastic, multiphase flow. Settari and Walters (1999) discuss the different methods that have been used to combine poroelastic calculations with porous flow calculations. They categorize these different methods of coupling poroelastic calculations with porous flow calculations as decoupled (Minkoff et al. 1999a), explicitly coupled, iteratively coupled, and fully coupled. The techniques discussed in this paper are explicitly coupled, iteratively coupled, and fully coupled.
Development of a Fully Coupled Approach for Evaluation of Wellbore Stability in Hydrocarbon Reservoirs