Comparisons of Uncoupled and Various Coupling Techniques for Practical Field Examples

Abstract

Generally, in classical reservoir studies, the geomechanical behavior of the porous medium is taken into account by the rock compressibility. Inside the reservoir simulator, the rock compressibility is assumed to be constant or to vary with the pressure of the oil phase. It induces some changes in the porosity field.During the depletion phase or the cold-water injection of highpressure/high-temperature (HP/HT) reservoirs, the stress state in and around a reservoir can change dramatically. This process might result in rock movements such as compaction, induced fracturing, and enhancement of natural fractures and/or fault activation, which continuously modify the reservoir properties such as the permeabilities and the fault transmissibilities.Modifications of such parameters strongly affect the flow pattern in the reservoir and ultimately the recovery factor.To capture the link between flow and in-situ stresses, it becomes essential to conduct coupled reservoir-geomechanical simulations.This paper compares the use of five types of approach for the reservoir simulations:• A classical approach with rock compressibility using only a reservoir simulator.• A loose coupled approach between a reservoir simulator (finite volumes) and a geomechanical simulator (finite elements). At given user-defined steps, the hydrocarbon pressures calculated by the reservoir simulator are transmitted to the geomechanical tool, which computes the actual stresses and feeds back iteratively the modifications of the petrophysical properties (porosities and permeabilities) to the reservoir simulator.• A one-way coupling: this approach is a simplification of the loose coupled approach in that the modifications are not fed back to the reservoir simulator.• A simplified approach using permeability and porosity multipliers inside a reservoir simulator. These multipliers are userdefined curves and vary with the pressure of the oil phase. This approach uses only a reservoir simulator.• A coupled approach in which the structural and the flow unknowns (displacement, pressure, and saturations) are solved simultaneously.These approaches are compared for two validation cases and two field cases described in the following.

Development of an Efficient Embedded Discrete Fracture Model for 3D Compositional Reservoir Simulation in Fractured Reservoirs

“…Gutierrez et al (2001) discussed the issues related to the interaction between rock deformation and fluid-flow behavior of hydrocarbon reservoirs. Moreover, Samier et al (2006) discussed and compared various approaches to perform coupled reservoir-geomechanical simulations.…”

A Review of Numerical Simulation Strategies for Hydraulic Fracturing, Natural Fracture Reactivation and Induced Microseismicity Prediction

“…The indirect or one-way coupling approach has been successfully used for optimization of relative simple fault/fracture reservoir production [73,74]. Also, technical literature shows some attempts to apply this methodology for modeling and validating natural fracture reactivation in unconventional reservoirs [75].…”

A multi-continuum multiple flow mechanism simulator for unconventional oil and gas recovery

“…The geomechanics module can synchronize with the reservoir simulation module at every Newton step, resulting in sequential coupling, or at every time step, resulting in explicit coupling. The sequential coupling is more accurate, while the explicit coupling is more adaptable to standard commercial geomechanic analysis tools (Samier et al, 2006). When using sequential coupling, the variables to be decoupled in Newton iterations should be chosen with caution, to guarantee stable convergence (Kim et al, 2011).…”