The effect of the rock type on the degradation of well cements in CO2 enriched geothermal environments

Abstract

The rock type plays a key role in the way in which the outermost layer of the cement interacts with the formation, in wells under geothermal environments. The penetration of cement into the rock is controlled by the porosity of the rock which also regulates the amount of CO2 enriched brine that can contact the cement. Samples were prepared by drilling holes into rock blocks, pouring in a cement slurry and hydrothermally treating the whole assembly at 150 °C under typical geothermal environments. The changes in the interfacial transition zone (ITZ) that forms between geothermal cements and volcanic rocks were examined. Both porosity and the volcanic glass content of the rock have a considerable impact on the way in which the cement and the formation interact and, ultimately, affect the bond between these materials. The porosity has a major influence on the durability of the cement in carbonated brine.