Abstract

A 3D finite-difference, fully implicit model has been developed to represent the physical phenomena occurring during the production from reservoirs with stress-sensitive mechanical and fluid-flow properties. The model considers two different physical domains:

  • an inner domain representing the reservoir, where fluid-flow and rock deformation occur, and

  • an outer (surrounding) domain representing the extended stress-disturbed region caused by reservoir depletion.

The inclusion of the surrounding domain leads to realistic modeling of the actual geomechanical boundary conditions taking place in the subsurface. The reservoir is treated as a multiphase poroelastic system consisting of a deforming solid skeleton and a moving compressible pore fluid. Non-linear elastic deformation ts assumed for both domains. The governing equations describing the deformation of the surrounding domain, the deformation of the reservoir solid skeleton and the motion of the pore fluid are fully coupled.

Simulation results clearly show that the permeability of stress-sensitive reservoirs may significantly change through the reservoir producing life. Different reservoir conditions yield different degrees of permeability reduction. In general, permeability decreases as production time increases. Zero- displacement boundary conditions yield less permeability reduction than constant stress boundary conditions. The permeability reduction decreases as the rock elastic moduli of the outer domain increase. The "arch effect" has a strong influence on reservoir permeability behavior.

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