Degradation of Well Cement by CO₂ under Geologic Sequestration Conditions

TLDR

Experiments assessed the durability of well cements exposed to CO₂ under geologic sequestration conditions by varying curing temperature and pressure. Cement cured at 50 °C and 30.3 MPa—representing sequestration conditions—exhibited greater resistance to carbonic acid attack, shallower degradation, and a well‑defined carbonated zone, likely due to a more uniform distribution of smaller Ca(OH)₂ crystals, whereas cement cured at 22 °C and 0.1 MPa showed greater initial degradation.

Abstract

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 °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 °C and 30.3 MPa (representing sequestration conditions) proved to be more resistant to carbonic acid attack than cement cured at 22 °C and 0.1 MPa. The cement cured at 50 °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.