Transient step permeametry on borehole cement and the effect of water.

Abstract

Recently the underground storage of CO2 has been suggested as an interesting concept for reducing the concentration of CO2 in the atmosphere. This research is focused on this method and investigates the permeability of cement used to seal the boreholes through which CO2 is injected underground. In addition, the effect of water on the permeability of cement has been tested. A transient step permeametry method is used to measure the permeabilities, and both CO2 and argon are used as permeametry fluids. The results for dry cement were as expected and comparable to results of earlier studies, with permeabilities in the order of 10-16 to 10-17 m2. Wet cement turned out to have significantly lower permeabilities caused by the presence of water. Three hypotheses were developed to explain the effect of water. It was concluded that two of them, precipitation of calcite and a lowered permeability as a result of capillary pressure, possibly take place, or a combination of these two processes. Furthermore there are indications that the Klinkenberg effect occurs in the samples. Calculations show the Klinkenberg permeability is lower than the permeabilities resulted from experiments, which was as expected. But this Klinkenberg permeability could only be determined for one sample and because of that it is not a very reliable conclusion.