Catastrophic crystal growth of clathrate hydrate with a simulated natural gas system during a pipeline shut-in condition

This paper presents a significant finding where capillary-aided catastrophic gas hydrate growth is observed under a shut-in condition (static fluid) for an uninhibited system. With the use of a newly designed apparatus, consisting of six units of identical rocking cell, nucleation and growth are observed. All experiments are conducted under isochoric conditions using 11.0 K subcooling (ΔT<inf>sub</inf>) as a driving force. A simulated natural gas mixture of 90.0 mol % methane + 10.0% mol % propane is used as a gas phase. The liquid phase used is 3% (Na⁺, Cl^-) brine. The observations of the capillary-aided mass-transport mechanism for a catastrophic gas hydrate growth are presented in this work. Our observations show hydrate crystal formation at a brine wetted area close to the brine/gas interface initiates capillary-aided catastrophic hydrate growth. Moreover, no mass transfer restriction of brine toward catastrophic gas hydrate growth is observed. Furthermore, our results show the denser (less porous appearance) hydrate structures are continuously displaced from the hydrate-water interface (hydrate growth side). This displacement allowed new hydrate crystals to be formed uninterruptedly until the exhaustion of water in the cells. On the basis of macroscopic observations, the capillary-aided mass-transport mechanism for a catastrophic gas hydrate growth is presented.