OCTG Connections Test Protocol for Underground Hydrogen Storage

Abstract Hydrogen storage is a key technology to deploy a sustainable hydrogen supply from producers to users. It can be massively stored underground in salt cavern through wells. Storage safety needs to be carefully managed especially by ensuring the gas sealability of hydrogen wells. Vallourec Research and Development department has investigated and evaluated a new qualification protocol for hydrogen storage to validate proprietary large integral premium connection for underground hydrogen storage. A 9-5/8″ 47.00# L80 proprietary threaded and coupled connection has been used by EnergyStock in a 1290m depth underground hydrogen test borehole in the Netherlands from February 2022 to January 2023. Several pressure cycles were made at 100% hydrogen in this storage. The storage pressure was 200 bar. Based on these real operating conditions, in 2024 a new hydrogen test protocol has been applied on 16″ 109# 110ksi premium integral connection. Indeed, some hydrogen well architectures feature tubing diameters up to 16″ with potentially higher pressure, higher temperature and high number of shallow cycles. The 9-5/8″ 47# L80 connection and the pipe were retrieved and inspected by Gasunie and Vallourec teams to check if any cracks or corrosion were visible. In order to cover a wider range of hydrogen storage applications, the protocol defined by Vallourec in 2021 has been improved and made more demanding. All tests are conducted with 5% H2/95% N2. A first sequence of 10,000 pressure cycles is performed at 475 bar with variations of +/- 25 bar to simulate daily loading and withdrawal operations. A second sequence to represent seasonal operations is conducted with pressure variations ranging from 30 to 500 bar and temperatures up to 180°C to cover a wide range of heating that may be encountered with the inverse Joule-Thomson effect. A third test sequence is conducted following Series B of API RP 5C5. Finally, a sequence of internal pressure testing is performed at 95% of the maximum pipe pressure. In addition, a 100% H2 pressure test is conducted on the connection to demonstrate its performance in pure hydrogen. A proposal is also made to submit the premium connection to external pressure with 5% H2/95% N2 to evaluate the impact of debrining operations on the connection. No current standard is available to assess OCTG connection for underground storage applications. The test protocol developed demonstrated that the connection evaluation is necessary for such application. The evaluated connection successfully passed the hydrogen test protocol. A return of experience on the connection performance in a salt caver after exposure to 100% H2 high pressure is also provided.