Hydrothermal High Temperature Cements For Potential Geothermal Applications

ABSTRACT New cementing materials with favorable physical properties are being developed for potential use at temperatures up to 400°C and pressures up to at least 70 MPa in geothermal well applications. One area of interest (in the lime-magnesia-silica-water system) involves the xonotlite-chrysotile join, and another area lies near the anorthite composition (in the lime-alumina-silica-water join), between about 45–65 weight percent silica. Phase formation and compatibility in the temperature region up to 300–400°C with pressures up to 69 MPa (10,000 psi) have been investigated, and the properties of the cementitious mixes formed have been evaluated. Replicate studies were made with different sources of starting materials, but commercially available starting materials were always included as an option. Mixes were evaluated primarily by means of measurements of compressive strength, water permeability, bond strength, and high temperature phase stability. Maintenance of pumpability at temperatures up to 177°C (350°F) has been demonstrated for magnesium-containing mixes. Detailed studies were made of the effects of alkalies (sodium and potassium) in the mixes upon the phases formed and stabilities of the cements. The magnesian compositions were found to be relatively stable, and any new phases formed did not have deleterious effects.