Abstract

This work presents a numerical framework, for the analysis of coupled fluid and geomechanical processes related to subsurface operations, built upon ABAQUS of SIMULIA, an industrial-standard software for mechanical analysis, and Echelon, a GPU-based reservoir simulator. By using porosity updates, the proposed framework can address both the impact of pore pressure changes on rock compaction as well as the the feedback of skeleton deformations on multiphase flow. Our solution is validated by means of various test cases. The results agree with analytical and reference solutions, showing that the proposed implementation of the iterative algorithm correctly accounts for strong coupling between mechanics and flow in porous media.

Introduction

The depletion of hydrocarbon reservoirs induces variations in time and space of reservoir pressure and saturation. In turn, changes in reservoir hydraulic properties may cause, following Terzaghi’s stress principle, a modification of the stress state in and around the reservoir. Stress changes can then influence the reservoir fluid parameters and alter the production scenario with the possibility of well mechanical failure, induced fracturing, fault reactivation and ground surface deformations. Nonetheless, the standard practice in the Oil&Gas industry is to assume that porosity – and permeability - are function of fluid pressure only and not of the stress state. This may not capture the coupling between flow and geomechanics, specially for weak hydrocarbon reservoirs, where the complex stress state and loading conditions give rise to complicated constitutive behaviour and stress-dependent reservoir properties [10, 11, 8].

Coupled hydro-mechanical analysis can be performed using either fully coupled or sequential methods. Unknowns for flow and mechanics are either solved simultaneously within a time-step (fully coupled or monolithic), or sequentially by splitting the problem into sub-problems. Fully coupled methods are attractive for general purpose simulations due to its unconditional stability [14]. However, they are computationally expensive and require the development of a unified flow–geomechanics simulation framework inside a single code.

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