The effect of gas void on restart pressure of waxy crude oil in pipeline

• This study investigates the impact of gas voids formed under carbon dioxide (CO 2 ) gas injection towards the severity of wax deposition issue. • CO 2 can act as carrier of larger gas voids which lead to reduction in restart pressure as well as giving a new perspective to CO 2 utilization initiative in the oil and gas industry. • This study concludes that CO 2 injection capable to reduce the restart pressure and the time taken for flow initiation of waxy crude oil in the pipeline during waxy crude oil production. • CO 2 injection not only makes the waxy crude more fluid and easier to transport but also significantly aids in managing the flow properties, thereby reducing the required pressure to restart the flow and improving the overall efficiency and safety of pipeline operations. Thermal shrinkage is one of the thermodynamic phenomena that occurs during waxy crude oil transportation in pipelines located on the seabed. In the case of scheduled or even non-scheduled production shutdown, thermal shrinkage occurs in waxy crude oil, which then forms solid deposits. Consequently, high pump pressure is required to instigate the waxy crude oil flow (restart pressure) in a blocked pipeline. Furthermore, thermal shrinkage can cause gas voids in the waxy crude oil, changing its compressibility factor. This study investigates the impact of gas voids formed under carbon dioxide (CO₂) injection on reducing restart pressure. Factors such as CO 2 injection pressure, temperature (WBT), and volume of CO 2 injected into the pipeline were investigated on the restart pressure of waxy crude oil flow using a waxy flow loop system. This study found that the optimum injection pressure is 3 bar with ± 5 % error margin at 20 °C and 35 °C WBT. The lowest restart pressure of 1.7 bar with ± 5 % error margin was recorded at the maximum CO 2 injection volume. The highest percentage of restart pressure reduction, which is 35.1 %, was observed at an injection volume of 200 mL across all WBTs investigated. This study concludes that CO 2 injection can reduce the restart pressure and the flow initiation time of waxy crude oil in the pipeline during transportation.