COMPARISON OF THE CHANGE OF CAP ROCK PERMEABILITY AND CAPILLARY ENTRY PRESSURE WITH VARYING EFFECTIVE STRESS

摘要

The determination of a cap rock formation’s capillary entry pressure is of major importance to determine the maximum non-wetting phase pressure that can safely be contained within a CO2 sequestration reservoir before the non-wetting phase begins to pass through the seal formation and leak out of the reservoir. Traditional experiments rely on unrealistically long experiment time frames,lasting up to several months in length for a single measurement. Alternative approaches have been developed,and there has been a thorough comparison performed between each of the techniques[1]. The conclusion of this comparison work is that a dynamic method is the quickest and most accurate measurement technique considered,where the change in the production rate of the wetting phase from the downstream end of the core sample before and after capillary entry and breakthrough have occurred can be related to the capillary entry and breakthrough pressure. This work focuses on the changes in permeability of a sample due to changes in the effective stress applied through the difference between confining fluid and pore fluid pressures. These changes in effective stress have been shown to have a significant impact on a sample’s permeability with ductile rock samples. The change in sample permeability is then compared to the effect of varying sample effective stress on the capillary entry pressure of the sample. Several experiments were performed on low permeability,high capillary entry pressure samples from an anhydrite mine and a carbonate sample received from Qatar.