Methane hydrates: Sampling and pressure core technology

Gas expansion in sediments mobilizes capillary forces that can cause extensive destructuration during sampling and core recovery. The situation is aggravated in marine and permafrost hydrate-bearing sediments as hydrate dissociation experiences a volume expansion of ~172 times. Pressure core technology prevents hydrate dissociation: unique samplers lock-in the in-situ fluid pressure and subsequent sediment characterization takes place without ever depressurizing the specimen. While the fluid pressure remains within the stability field, specimens experience changes in effective stress. Samplers and test chambers must be carefully designed, and test protocols meticulously executed to obtain reliable properties for analyses and design. Lessons learned in geotechnical engineering and experimental results obtained with hydrate-bearing sediments help advance pressure core sampling and testing technology. The technology has been deployed to study hydrate-bearing sediments in the Gulf of Mexico (USA), Krishna- Godavari Basin (India), Ulleung Basin (S. Korea), and Nankai Trough (Japan).