Effect of Injection Strategy of CO2 with Impurities on Cement Integrity

Abstract Carbon capture and storage (CCS) operations are increasingly confronted with challenges posed by CO2 impurities, which are difficult and costly to eliminate. This study investigates the impact of industrially relevant CO₂ impurities, such as N₂, CH₄, H₂, O₂, H₂S, and SO₂, on the thermal behavior of CO₂ injection and its implications for cement integrity. Using the transient multiphase flow software, the Joule–Thomson (JT) cooling effects and enthalpy variations across a range of injection scenarios are modeled for both post-combustion (PC) and natural gas processing (NGP) CO₂ streams. Binary stream analysis (CO2 with a specific impurity) shows that non-condensable gases have a higher JT coefficient and lower enthalpy, leading to sharper temperature declines along the wellbore but within a more restricted area. Condensable gases have the opposite effect. Simulation outcomes for PC and NGP streams reveal significant impurity-driven changes in wellhead pressures up to 23.9%, but minor changes for downhole temperatures within 10%. For supercritical and liquid phase, the temperature drop significance is PC > NGP > Pure CO2, while for gas phase, the temperature drop significant is NGP > Pure CO2 > PC. The main reason for this is the JT coefficient at different pressure and temperature. The downhole choke effect on wellbore cooling was also investigated, and results show that the use of a downhole choke is a promising solution for injecting cold CO2 into depleted oil and gas reservoirs. Well integrity analysis reveals that cement properties are important, and due to potential interaction between CO2 and cement, the alteration could reduce the well's capability in handling high injection rate. An idea cement system for CO2 injection wells should have proper thermal, hydraulic, mechanical, and chemical performance.