Lightweight CO2-Resistant Cements for Geothermal Well Completions

Abstract

Materials formed hy acid-base reactions between calcium aluminate compounds and phosphate-containing solutions yield high strength, low permcability and cements when cured in hydrothermal environments. The cementing formulations are at temperatures up to 150?C. thercby making their use for well completions technically feasihle. When this cementing matrix was exposed in an autoclave containing brine for 120 days, CaCO, was produced. A conventional portland cement-based well completion material will form -10 CaCO, after only 7 days exposure. The addition of hollow aluminosilicate microspheres to the uncured matrix constituents yields slurries with densities as low as -1.2 gicc which cure to produce materials with properties meeting the criteria for well cementing. These formulations also low rates of carbonation. Lahoratory characterization is nearing completion. engineering scale-up is underway. and plans for field testing in a variety of geothermal fluids are being made.