CO2 Injection Well Transients: How Complex Can They Be?

Abstract For CO2 injection wells, it is imperative to develop a comprehensive understanding of the operating envelopes under transient conditions. This understanding is essential for several reasons, including the development of a phase behavior management plan, the identification and mitigation of wellbore instability and unexpected phase changes, and the assessment of impacts on the formation. Understanding the transient behavior is crucial for designing more effective injection strategies, reducing downtime, and enhancing overall operational efficiency. This paper aims to investigate the transient operations pertaining to CO2 injection wells, focusing on transient scenarios such as diesel expansion in the annulus, choke failure, depressurization, and the start-up and shut-down processes. The primary objective is to analyze the conditions within the tubing and surface network during these transient events and to understand their impacts on the injection system. The study involves the simulation of transient operations that might occur in a CO2 injection well. A detailed well model is built in a transient multiphase simulator to simulate CO2 injection in a saline aquifer with various transient operations modeled to understand the impact of transients on the surface network and the tubing. Pure and CO2 with impurities are considered to understand the impact of impurities on these transient events. The simulations reveal significant pressure/temperature variations during transient operations which need to be incorporated when designing a CO2 injection well to ensure wellbore integrity and safe operation. The study concludes with guidelines to be followed during transient operations and mitigating risks associated with transient conditions in wells. This paper provides novel insights into the behavior of CO2 injection wells during transient operations, highlighting the importance of designing wells capable of handling short and long transients. The findings offer valuable recommendations for industry practices, contributing to the optimization of CO2 injection operations and enhancing the overall safety and efficiency of the process.