Application of downhole throttling technology to mitigate sustained casing pressure

Abstract

Sustained casing pressure (SCP) and/or annular pressure build-up (APB) can pose severe threats to the safe operation of high-pressure, high-production gas wells, leading to premature well abandonment, unplanned workovers, significant production losses, and exorbitant detection costs. The techniques for addressing these issues broadly fall into two categories of rig-based and rig-less workovers. The rig-less workovers are the most cost-effective, outperforming surefooted rig-based workovers because there are many techniques for detecting downhole leaks, especially those utilizing rig-less data. As an established technique used elsewhere in the petroleum industry, downhole chokes have been proposed to mitigate SCP. However, some critical questions remain unanswered. For this reason and to facilitate field applicability, essential parameters, such as choke depth, are optimized in this work under various leaking circumstances in the tubing string. By using commercial software, the evolution of the annulus pressure with one single leak is analysed under the influences of certain parameters, such as leakage depth, casing pressure relief, production shifts, and initial gas column height in the tubing/casing annulus; then, the patterns of fluid exchange between the tubing and casing string and the annular pressure rise are investigated for two successive leaks. Finally, based on the resulting insights, the adaptability levels of downhole throttling technology for mitigating SCP are investigated under various scenarios with either single or double leaks. The results show that the key to success is to land below the leak for a single leak and below the lower leak for double leaks. The conclusions provide a low-cost, rigid measure for abating SCP.