Effects of Carbon Dioxide Attack on Geothermal Cement Grouts

Abstract

Studies of carbonation of geothermal grouts have shown that the physical criteria recommended by the American Petroleum Institute do not apply for durability in CO2 containing fluids. The high silica binders, normally considered desirable because of their high strengths and low permeability, become permeable when carbonated. This allows further attach on the grout, and if the fluids are under saturated with CaCO3, then rapid corrosion will occur. On the other hand, grouts which contain appreciable amounts of calcium hydroxide have proved the most durable in CO2 containing fluids despite their low strengths and high permeability. This is due to an impermeable layer of calcium carbonate which forms on the outside of the sample preventing further penetration of reactant species. Unless this layer is corroded, no further attack occurs.