Dynamic Effect in Capillary Pressure- Saturation Relationship and its Impact on Unsaturated Flow

Recent theories indicate that capillary pressure is perhaps not only a function of saturation but also rate of change. This is known as the dynamic effect. A comprehensive review of experiments reported in the literature is presented. The experiments provide ample evidence that a dynamic effect is observable and even quantifiable. The reported data are used to estimate the coefficient that arises in the theory. It was found that range of values of the dynamic coefficients spans about four orders of magnitude. To examine whether these coefficients have any practical effects on larger-scale problems, a continuum-scale simulator was constructed in which the dynamic effects are included. Results of our simulations indicated that the dynamic effect may be important for some field situations. Numerical simulators for unsaturated flow should generally include the additional term(s) associated with dynamic capillary pressure