Sandstone water sensitivity: Existence of a critical rate of salinity decrease for particle capture

A critical rate of salinity decrease (CRSD) was found to exist in the water sensitivity of Berea sandstone. The CRSD was determined by conducting core flood experiments in which the salinity was decreased exponentially by placing mixers of various volumes in the inlet stream. Above the CRSD, drastic reductions in core permeability occur due to a log jam, or bridging effect, at the pore constriction. Below the CRSD, the released clay particles pass through the constriction without being captured and therefore very little reduction in core permeability occurs. A critical particle concentration was also identified above which bridging occurs. Based on the experimental observations, a mathematical model was developed to delineate the regions of high and low permeability reductions. The model predictions are in good agreement with experimental measurements.