Experimental Study on Memory Effect of Gas Hydrates: Interaction between Micronanobubbles and Solute Molecules

Worldwide natural gas hydrates are considered the largest hydrocarbon source. A challenge in accessing these resources is the memory effect exhibited by gas hydrates, in that gas hydrate nucleation is more rapid in solutions in which gas hydrate has previously decomposed. A number of hypotheses exist to explain this memory effect, including the proposal that nanobubbles play a role. Bulk nanobubbles show surprising stability and have been implicated in gas hydrate nucleation and growth. Here the influence of both surface and bulk nanobubbles on the hydrate memory effect are explored. The presence of both surface and bulk nanobubbles were confirmed in hydrate decomposition solutions by different methods. The influence of nanobubbles on the memory effect was demonstrated through the influence of degassing on the induction time and nucleation probability estimation. Also, the hydrate nucleation and growth characteristics on the surface of bulk micronanobubbles in pure water, electrolyte, and surfactant solutions was studied. It was shown that gas hydrate crystals coated bubbles in pure water, but the formation of this coating was inhibited in surfactant solutions. Electrolyte also inhibited the coating of bubbles with hydrate crystals. This work demonstrates that nanobubbles strongly influence the memory effect in gas hydrates, by both directly influencing gas hydrate nucleation and through wall effects via surface nanobubbles. This work does not preclude other mechanisms proposed for the memory effect in gas hydrate formation.