CO2 injection modeling in a reservoir: Phase transition study

Resumo

The study explores the phase transition of carbon dioxide from liquid to gas after injection and storage in a confined aquifer at a temperature of 30°C. By utilizing a compositional isotropic model and data from the NIST webbook (Linstrom and Mallard, 2024), the simulation analyzes, using compositional mesh model in tNavigator software (by Rock Flow Dynamics), the behavior of CO2 within a confined aquifer, seeking to identify the phase transition of the fluid. The effects of capillarity are neglected, and the main parameters of the reservoir are a pressure of 65 bar at the wellhead and a constant temperature of 31°C throughout the aquifer to evaluate the phase transition close to the supercritical point of CO2.
The analysis reveals that the drastic pressure reduction within the confined aquifer leads to the formation of free gas within the reservoir after the closure of injection wells, which becomes a problem, as occurred in the Ordos CCS Project in China, allowing fluid backflow during non-injection (CAI, Yuna et al.). The results showed that the closer the temperature approaches the supercritical point of CO2, the greater the probability of free gas formation within the reservoir.
Therefore, the conclusions emphasize the impact of the pressure reduction on the stability of CO2, which will undergo a phase transition from the liquid to the gaseous state, so that free gas is generated within the reservoir. In this way, it is highlighted the importance of understanding phase transition in CO2 injection processes for effective carbon capture and storage strategies.