Qualification Approach of OCTG Connections for CCS Injection Wells Tubing and Casing

Carbon capture and storage is seen as a key solution to engage in the global energy transition, however the operating conditions of the CO2 injection wells brings new challenges to connections for tubing string such as extreme low temperatures (-78°C), quick variations of temperature as well as transient phase of the CO2 that may affect connections integrity, end-finish and lubricants used. Such conditions are not limited to tubing string but also reach casing string due to radial thermal propagation in the well. This may induce low temperature on casing string and freezing of the completion fluid inducing high pressure variation: internal pressure on casing and external pressure on tubing. The current paper describes a study of the thermal gradient that may occurs for different life scenario and present test protocols which focus on CCS specificity for both casing and tubing to efficiently assess OCTG premium connections. A numerical simulation is primarily used to understand the impact of quick drop of temperature, due to the Joule-Thomson and phase changes effects during depressurization, on the connection integrity and sealability. To correlate this simulation, the tubing connection is submitted to a dedicated test protocol relevant to CO2 injection conditions which consider high number of pressure and temperature cycling, thermal shock and sealability with thermal gradient between Pin and Box. Latest work and simulations allow us to assess the radial heat transfer and estimate the casing temperature at different depth of the well. Based on these, a specific test protocol to assess premium connection on bigger diameter, used for casing string and demonstrate their suitability for CCS wells is proposed. Thanks to numerical simulation and research collaboration, a complementary test protocol for casing was build and allow to fully cover CCS specific load cases. Tubing and casing test protocols both allow to guarantee the integrity and sealability of premium OCTG connections with a relevant process. The combination of numerical simulation, material study, and dedicated test protocol allow to build a complete qualification approach and support to operators when designing future CCS well.