Development of a Test Protocol to Evaluate OCTG Dope-Free Connection Response to Cryogenic Conditions that could appear in Extreme Load Cases of CCS Projects
Authors: Nutricato Giacomo , Repetto Carmen , Santoro Domenico , Zucchetto Maria Ornella , Dal Forno Luca , Curioni Emilio , Brambilla Ruggero , Eaton Roger , Martini Luca , Nunzi Paolo , Chiu Yen-ni , Nicolò Simone , Mantegazza Tommaso , Gibellini Erica , Goya Martin , Zambetti Raffaello , Santi Nestor 
Published: April 2023

In the need for world decarbonization, the idea of utilizing available, suitable and/or depleted oil and gas reservoirs to inject CO2 has become a new objective for energy companies, this is the so-called Carbon Capture and Storage (CCS) application. Though injecting CO2 is not new for the industry as Enhanced Oil Recovery (EOR) has been thoroughly used around the globe, the particularities of injecting CO2 at a greater scale impose new challenges from the metallurgical and mechanical perspectives.

During the injection of CO2, the string will be subjected to loads and pressures that will be generally low when compared to the performance of the pipes and modern gas-tight Metal-to-Metal seal OCTG premium connections. The main concern of this application is typically associated with the CO2 behavior and the thermodynamic loads produced during the injection. In a steady state condition and depending on the reservoir pressure, temperatures could drop as low as -20/-35°C. In a less probable scenario of a sudden exposure of the CO2 in the well to the atmospheric pressure, the expansion could produce a further reduction in temperature due to Joule-Thomson (J-T) effect reaching a theoretical limit of approximately -78°C.

The purpose of this experimental activity is to evaluate by means of numerical analysis and physical full-scale test, the behavior of a gas-tight dope-free premium connection when subjected to low temperatures and loads generated by CO2 expansion during injection in depleted reservoirs. In particular, the extreme reduction in temperature in case of an uncontrolled release into the atmosphere is investigated. For this purpose, a connection is exposed to a temperature of around -78°C, and both its structural and sealing responses are verified. The analysis is performed considering estimated loads for a CO2 injection case study.

The results of the evaluations demonstrate that neither the structural capacity nor the sealing response are affected by the sudden temperature drop. Additionally, these results are also confirmed by the numerical evaluations. In the simulation, well loads affected by the additional tensile stresses produced by the contraction of the constrained string remain well inside the connection service envelope. The combination of these two tools defines a state-of-the-art methodology for assessing premium connection under cryogenic temperatures in CCS projects.

The results achieved by the premium connection subjected to a thermal shock of nearly -78°C represent a forefront in the industry. The experiment, demonstrated that the product maintains its full reliability in operative conditions after being subjected to an extreme event related to the application risks, confirming its adequate performance in CO2 injection and storage projects.