Nonportland Cement-based Systems for Geothermal Well Use

Portland cement for high-temperature geothermal applications typically includes 35 to 40 percent crystalline quartz by weight of cement (BWOC) to avoid strength retrogression, which is defined as an increase in permeability and a decrease in compressive strength. Also, because of the reactivity of Portland cement at elevated temperatures, relatively expensive cement-hydration retarders are required. One alternative to Portland cement is the use of a calcium hydroxide Ca(OH)2 silica SiO2 cement. Calcium hydroxide mixed with silica and water forms hydraulic cement composed of crystalline phases at high temperatures. The reduced reactivity of the system allows the cement to be placed in a wellbore at extreme temperatures. In this work, examples of calcium hydroxide silica cements are discussed. Information on the hydration time, mechanical properties, and crystalline-phase analysis are discussed. A discussion of this work and ongoing research in this area will be provided.