Study on prediction of sustained casing pressure in tubing-casing annulus based on bubble migration experiment

Abstract

Sustained casing pressure (SCP) due to tubing leakage is an unwanted condition for well barrier reliability and gas well management and can affect well integrity. Therefore, studying the SCP prediction in the tubing-casing annulus to reduce the potential risk in the wellbore is critical. Almost all available research neglects the effect of the migration of the gas in the annulus on the SCP. In this research, a prediction model of the SCP is developed by integrating the gas migration. Meanwhile, a device is being experimentally developed according to the similarity principle. Based on the simulation experiments, the gas migration characteristics are investigated, and the accuracy of the prediction model of the gas migration is verified. Then, a numerical model is established for the SCP to further evaluate the validity of the SCP prediction model and the effect of the gas migration on the SCP. Finally, a case study is conducted on a high-pressure gas well of the SCP to investigate the effects of the condition parameters of the well on the SCP and the gas migration. The obtained results indicate that the position of the tubing leakage and the liquid density in the annulus has an impact on the balance value and recovery rate of the SCP. The gas migration has no effect on the balance value of the SCP, but it does alter the initial recovery rate of the SCP. The work presented provides a reliable prediction method for the accurate description of the SCP process.