Hydrate Reformation from the Joule-Thomson Effect in Illite-Containing Sediments

Hydrate reformation significantly impacts the gas production rate during the depressurization processes. However, compared to sandy sediments, there are potential differences in the hydrate reformation behaviors in clayey sediments. This study conducted gas seepage experiments in a one-dimensional 2.6 m reactor. The influence of the pressure difference on the hydrate reformation behavior, temperature, pressure, and permeability of the sediment containing illite was experimentally analyzed based on the Joule-Thomson (JT) effect. Results demonstrate that the JT effect increased with a higher pressure difference, thereby accelerating the rate of hydrate reformation. The JT effect intensified at distances of 1.2 and 1.6 m from the wellbore due to illite migration, enhancing both the temperature drop and the reformation driving force. Hydrate reformation onset, predicted based on the reformation driving force, occurred approximately 2 m away from the wellbore. Blockage occurred within an 11 cm range near the wellbore. After blockage formation, the pressure represented a fluctuating increase, further promoting the hydrate reformation. Permeability decreased drastically, with the damage rate exceeding 60% near the wellbore. Conversely, there was no permeability decline in the case where hydrate reformation occurred without blockages. This study emphasizes the impact of illite migration on hydrate reformation, providing insights into fluctuations and declines in gas production rates observed during production tests.