Assessment of hydrate flow obstacles during the initial restarting period of deep-water gas wells

Abstract

Hydrate flow obstacles encountered during the exploitation of deep-water gas fields has received an increased attention. Based on the variations in the wellbore temperature of a deep-water gas well during the initial restarting period, and considering the interrelationship between the hydrate behavior and heat transfer, a prediction model for hydrate flow obstacle was established by comprehensively considering the hydrate formation, deposition, and decomposition. This model could be used to analyze the hydrate formation and decomposition regions dynamically and depict the evolution of the hydrate plug quantitatively during the restarting period. The computation results demonstrated that the wellbore temperature increased with the restarting time, which caused the hydrate formation region to decrease accordingly. During the initial restart under testing operations, hydrates always formed at low gas production rates in the tubing, which could plug the tubing after a certain restarting time. The risk of hydrate flow obstacle first increased and then decreased with an increase in the restarting production rate. During the initial restart under production operations, hydrates only formed at the initial restarting stage, which ranged from several minutes to more than 10 h. The hydrate flow obstacle risk first increased and then decreased with the restarting time, and no hydrate plugging occurred during the initial restarting period of the entire production process. Finally, the measures for preventing hydrate plugging during the initial restarting period were discussed. This work provides a valuable theoretical reference for preventing hydrate plugging during the initial restarting period of a deep-water gas well.