Well completion and integrity evaluation for CO2 injection wells

Sequestration of CO2 in depleted oil and gas reservoirs, coal seams and saline aquifers is one important means of mitigating greenhouse effect on the environment and enhancing oil and gas recovery. The collected CO2 is injected via injection wells into the underground space. Due to the characteristics of supercritical CO2, e.g., corrosive, low temperature, the well design and completion for CO2 injection purposes requires more considerations. This paper introduces the basic challenges of designing a CO2 injection well, reviews the famous CO2 injection cases around the world, and proposes well completion criteria, including completion scheme design, materials selection and so on. Well integrity tests in use are reviewed and evaluated in terms of their pros and cons. Well integrity evaluation using numerical simulation is conducted as well to study the influences of CO2 injection on well integrity in a pilot area in Germany. The results show that the materials selected for CO2 injection well shall adapt to the low-temperature environment, and the cement should have a high tensile strength and resist corrosion. Under the impact of salt rock creep, the cement cracks resulting from temperature decrease during injection tend to heal. At the end of the paper for the wells with loss of integrity, a remedial work needs to be done, e.g., cement repair, and for this a thorough review of cement repair experiences is performed.