Pressure Transient Behavior of Stress-Sensitive Reservoirs
T.A. Jelmert, H. Selseng · 1997
The choice of state variable in the non-linear diffusion equation may be of importance when analytical solutions are desired. The behavior of stress-sensitive reservoirs can best be predicted when the diffusion equation is formulated in terms of a permeability-like variable. Then the resulting equation becomes practically linear and approximate analytical solutions are possible.We find that the validity of a steady state skin factor is uncertain for stress-sensitive reservoirs. Different conceptual models are possible. A skin factor based on the equation of steady state flow in a stress-sensitive reservoir is recommended.The most common linearization techniques, the Cole-Hopf and the Kirkhoff transformation, are equivalent when the permeability pressure relationship is given by an exponential function.A material interface leads to a discontinuity in the transformed variable. The jump condition is given by powerlaw relationship. Hence application of linearization techniques to layered and commingled reservoirs may be problematic. We find that the technique may be applied when the modulus to permeability is approximately the same in each layer.