Degradation of Well Cement by CO2 under Geologic Sequestration Conditions

Experiments were conducted to assess the durability of cements in wells penetrating candidate formations for geologic sequestration of CO2. These experiments showed a significant variation in the initial degradation (9 days of exposure) based on the curing conditions. The high-temperature (50 degrees C) and high-pressure (30.3 MPa) curing environment increased the degree of hydration and caused a change in the microstructure and distribution of the Ca(OH)2(s) phase within the cement. Cement cured at 50 degrees C and 30.3 MPa (representing sequestration conditions) proved to be more resistant to carbonic acid attack than cement cured at 22 degrees C and 0.1 MPa. The cement cured at 50 degrees C and 30.3 MPa exhibited a shallower depth of degradation and displayed a well-defined carbonated zone as compared to cement cured under ambient conditions. This is likely due to smaller, more evenly distributed Ca(OH)2(s) crystals that provide a uniform and effective barrier to CO2 attack.