Productivity Changes in Reservoirs With Stress-Dependent Permeability

Summary The goal of this paper is to present correlations to permit engineers to evaluate productivity losses in reservoirs with stress-dependent permeability (stress-sensitive reservoirs). The correlations developed in this study are intended to be used in determining production forecasts. For stress-sensitive reservoirs, the reduction in permeability caused by the change in the stress state during production (if any) may significantly reduce expected productivity. It is the purpose of this paper to address methods to ascertain changes in productivity as a result of stress-dependent permeability. A rigorous mathematical model that couples geomechanical and fluid-flow aspects is used to correlate productivity reductions with time. The reduction in the productivity index (PI) is quantified by a skin factor and is expressed as a function of operating variables such as overburden stress, mechanical properties, wellbore pressure, and drainage area. The expressions developed in this study may be incorporated directly (after tuning) in simulators to properly account for changes in productivity.