oa On Backflow in a CO2 Injection Well During Transient Operations

This paper utilizes the OLGA code, an enhanced commercial flow assurance tool for CO2 applications, to evaluate the potential backflow of CO2 injection wells under different storage conditions. The OLGA simulation accurately predicts the thermal dynamics of the CO2 stream in the Snøhvit CO2 injection well during its shut-in period. The simulation results show that there is no backflow from the reservoir into the CO2 injection well during normal operational conditions, such as the shut-in of the wellhead choke, if the CO2 entering the well has the same temperature as the ambient temperature, regardless of whether the CO2 is single-phase or two-phase flow in the well prior to or during the shut-in period. However, backflow into the well may occur when the CO2 temperature at the wellhead is higher than the ambient temperature. If the flow assurance tool is coupled with a reservoir simulator, the amount of backflow volume and fluid composition can be accurately predicted. Backflow is not expected to be an issue during continuous CO2 injection into the well, but it may occur if the pipeline and well system experience large-scale unstable flow, such as slugging.