Physical property changes in hydrate-bearingsediment due to depressurization and subsequent repressurization

Physical property measurements of sediment cores containing natural gas hydrate are typically performed on material exposed at least briefly to non-in situ conditions during recovery. To examine effects of a brief excursion from the gas-hydrate stability field, as can occur when pressure cores are transferred to pressurized storage vessels, we measured physical properties on laboratory-formed sand packs containing methane hydrate and methane pore gas. After depressurizing samples to atmospheric pressure, we repressurized them into the methane-hydrate stability field and remeasured their physical properties. Thermal conductivity, shear strength, acoustic compressional and shear wave amplitudes and speeds are compared between the original and depressurized/repressurized samples. X-ray computed tomography (CT) images track how the gas-hydrate distribution changes in the hydrate-cemented sands due to the depressurization/repressurization process. Because depressurization-induced property changes can be substantial and are not easily predicted, particularly in water-saturated, hydrate-bearing sediment, maintaining pressure and temperature conditions throughout the core recovery and measurement process is critical for using laboratory measurements to estimate in situ properties

cylindrica

Heuchera cylindrica Douglasheuchère cylindriqueRound-leaved alumrootPrairie BluffT. ChisholmS. facing scree slope consisting of red, black, and brown layers of shale2132 mTownsendia condensata, Cryptantha macounii, Mertensia lanceolata, Dasiphora fruticosa, Anemone multifida, Pinus flexilis, Saxifraga bronchialis, Erigeron compositus, Viola adunca, Clematis occidentali

cylindrica

Heuchera cylindrica Douglasheuchère cylindriqueRound-leaved alumrootPrairie BluffT. ChisholmS. facing scree slope consisting of red, black, and brown layers of shale2132 mTownsendia condensata, Cryptantha macounii, Mertensia lanceolata, Dasiphora fruticosa, Anemone multifida, Pinus flexilis, Saxifraga bronchialis, Erigeron compositus, Viola adunca, Clematis occidentali