The assumption of constant rock properties in pressure-transient analysis of stress-sensitive reservoirs can cause significant error in determination of reservoir transmissibility and storativity. On the other hand, inclusion of pressure-dependent rock properties makes the governing equation for the pressure in the reservoir nonlinear. These nonlinearities can be treated only approximately by numerical means. If a permeability modulus is defined, the nonlinearities associated with the governing equation become weaker and an analytical solution in terms of a regular perturbation series can be obtained for a radial infinite-acting reservoir. Three terms in the perturbation series are derived to show the convergence and accuracy of the solution. The equation obtained for each order (zero, first, and second) in the perturbation series is solved exactly, and hence, the solution is exact to the third order.
The effect of wellbore storage on the pressure behavior is also investigated. First-order approximation for bounded systems is presented to show qualitative effects. A field example is analyzed to determine the permeability modulus and reservoir properties.