Stress effects on flow partitioning in fractured reservoirs: equivalent porous media versus poro-elasticity coupled modeling.

摘要

In this paper the effects of overburden stress on fracture-matrix flow partitioning were numerically analyzed using two different numerical approaches; the analysis was validated using a fractured Clashach core flood laboratory experimental data. In the first numerical approach, the fracture aperture variation under different overburden stresses, measured using a back calculation method based on the treatment of the fracture as an equivalent porous medium, was adopted in a coupled Darcy law, Brinkman flow and Navier-Stokes fluid flow formulation. In the second numerical approach, poro-elasticity was applied in order to accurately account for fracture aperture change under overburden stress loading. The resulting displacements were coupled to the same fluid flow equations used in the first approach through a moving mesh technique. This was further coupled with stress dependent permeability within the matrix. Flow partitioning from the two numerical approaches were compared to the experimental data. This comparison highlighted the inefficiency of treating fractures as equivalent porous medium. Moreover the cross-flow between the fracture and the matrix was monitored in both modeling approaches and a critical stress beyond which the matrix can no longer feed the fracture was identified. This critical stress can be very important in designing production scenarios for highly-stressed fractured reservoirs.