Degradation of well cement in HPHT acidic environment: Effects of CO2 concentration and pressure

After exposure, incomplete hydration of clinker materials, carbonation of cement hydrates, leaching of by-products of carbonation, and structural transformation of amorphous calcium silicate hydrate to its crystalline form were observed. Generally, compressive strength increased with CO2 concentration due to carbonation of calcium hydroxide (CH) and calcium silicate hydrate (C-S-H). Correspondingly, porosity and permeability decreased. Furthermore, degree of degradation is greatly influenced by pressure.