| Popis: |
This study investigated the sealability of premium threaded joints (PJs) in carbon dioxide capture and storage (CCS) wells using finite element analysis (FEA) and small-scale fundamental gas tightness tests. During the operation of CCS wells, the inner surface of the tubing can reach extremely low temperatures. This cooling may decrease the metal-to-metal seal contact energy and/or change the viscoelastic properties of the applied lubricants, affecting the sealability of the PJs. Firstly, the extreme temperature differential, simulating the worst-case transient state in a tubing, was evaluated using FEA, in which the PIN inner surface was simulated at -80 °C and BOX outer surface was maintained at 25 °C. Secondly, the impact of different lubricating systems on sealability was evaluated via small-scale fundamental gas tightness tests under extremely low-temperature conditions. Additionally, dynamic viscoelasticity measurements for lubricants under extremely low-temperature conditions were conducted. The FEA results indicated that the impact of the temperature change on the minimum seal contact energy while applying a combined loading cycle was limited, even though the temperature of the metal seal surface was cooled to approximately -40 °C under an extreme temperature differential. Small-scale tests demonstrated that the sealability of an environmentally friendly thread compound (the so-called yellow dope) and solid lubricating film were equivalent to or higher at -40 °C than those observed at 25 °C. By contrast, an API dope, which is the standardized thread compound for PJs specified by the American Petroleum Institute (API), has a low sealability at -40 °C. By measuring the dynamic viscoelasticity of these lubricants, we demonstrated that an API dope can exhibit a glass transition point at approximately -50 °C, while the yellow dope transition occurred at approximately -75 °C. This difference in viscoelasticity properties at extremely low temperatures corresponds to the changing sealability characteristics. Specifically, an excessive increase in viscosity (API dope) would deteriorate the sealability, while a minor increase in viscosity (yellow dope) would improve the sealability. Dynamic viscoelasticity measurements also demonstrated that the properties of these dopes once cooled to -80 °C returned to their original states after heating to 25 °C. This indicates that PJs are also expected to retain their original sealability performances after being subjected to extreme temperature hysteresis. |
