Effects of fractures on reservoir deformation and flow modeling

Abstract

Fracture opening and closure caused by changes in the effective stress on fracture planes is well known. This phenomenon happens in aquifers and hydrocarbon reservoirs where production or injection events change the applied effective stress. Modeling this phenomenon requires a rigorous coupled geomechanics and flow simulator as well as detailed information regarding fracture properties, spacing, and orientation. A method has been developed to account for the effects of fractures on deformation in coupled reservoir and geomechanics simulation. The equivalent continuum approach was used where the constitutive matrix of individual blocks was calculated by means of an analytical formula that considers both rock and fracture deformation properties. The rock material is assumed to be isotropic and the normal stiffness of fractures varies with the applied effective stress according to a law that is typical for joints. The shear deformation of the fractures can be incorporated easily in the future. The general pseudo-continuum model was verified by comparing it with an approach using explicit modeling of the fractures. The fractured rock geomechanics model is then coupled to a single porosity, multiphase flow model. The deformations produce changes in the permeability tensor in both magnitude and orientation, which in turn influences compaction behavior.Key words: fracture deformation, equivalent moduli, coupling, reservoir compaction, reservoir simulation.