Elevated LNG Vapour Dispersion—Effects of Topography, Obstruction and Phase Change

The dispersion of vapour of liquefied natural gas (LNG) is generally assumed to be from a liquid spill on the ground in hazard and risk analysis. However, this cold vapour could be discharged at height through cold venting. While there is similarity to the situation where a heavier-than-air gas, e.g., CO2, is discharged through tall vent stacks, LNG vapour is cold and induces phase change of ambient moisture leading to changes in the thermodynamics as the vapour disperses. A recent unplanned cold venting of LNG vapour event due to failure of a pilot, provided valuable data for further analysis. This event was studied using CFD under steady-state conditions and incorporating the effect of thermodynamics due to phase change of atmospheric moisture. As the vast majority of processing plants do not reside on flat planes, the effect of surrounding topography was also investigated. This case study highlighted that integral dispersion model was not applicable as key assumptions used to derive the models were violated and suggested guidance and methodologies appropriate for modelling cold vent and flame out situations for elevated vents.

Chemosynthetic bivalves of the family Solemyidae (Bivalvia, Protobranchia) in the Neogene of the Mediterranean Basin

The Mediterranean area is the locus of a variety of deep-sea chemosynthetic environments that have been exploited by bivalves of the family Solemyidae during Cenozoic to present time. Large solemyids represented by theSolemya doderleinigroup were widely distributed in Neogene deep-sea reducing habitats, including cold vent hydrocarbon sites. Based upon the diagnostic structure of the ligament,Solemya doderleini(Mayer), 1861 andS. subquadrata(Foresti), 1879 are moved to the genusAcharaxDall, 1908. After the Messinian Salinity CrisisAcharax doderleinire-colonized deep-sea sulphide environments up to the Pliocene at least. At present,Acharaxoccurs in similar settings in the adjacent eastern Atlantic Ocean. Thus far, large solemyids are not documented from the present deep Mediterranean Sea in spite of a vast number of seep and reducing habitats with chemosynthetic biota, especially concentrated in its Eastern basin. Promisingly, however, a single live juvenile specimen of Solemyidae has been recently found at bathyal depth associated with a pockmark in the Nile Deep Sea Fan.

Imaging a hydrate-related cold vent offshore Vancouver Island from deep-towed multichannel seismic data

The Bullseye vent, an approximately [Formula: see text]-diameter deep-sea, hydrate-related cold vent on the midslope offshore Vancouver Island, was imaged in a high-resolution multichannel survey by the Deep-towed Acoustics and Geophysics System (DTAGS) The structure was drilled by the Integrated Ocean Drilling Program at site U1328. Towed about [Formula: see text] above the seafloor, the high-frequency [Formula: see text] DTAGS system provides a high vertical and lateral resolution image. The major problems in imaging with DTAGS data are nonlinear variations of the source depths and receiver locations. The high-frequency, short-wavelength data require very accurate positioning of source and receivers for stacking and velocity analyses. New routines were developed for optimal processing, including receiver cable geometry estimation from node depths, direct arrivals and sea-surface reflections using a genetic algorithm inversion method, and acoustic image stitching based on relative source positioning bycrosscorrelating redundant data between two adjacent shots. Semblance seismic velocity analysis was applied to common-reflection-point bins of the corrected data. The processed images resolve many subvertical zones of low seismic reflectivity and fine details of subseafloor sediment structure. At the Bullseye vent, where a [Formula: see text]-thick near-surface massive hydrate layer was drilled at U1328, the images resolve the upper part of the layer as a dipping high-reflectivity zone, likely corresponding to a fracture zone. Velocity analyses were not possible in the vent structure but were obtained [Formula: see text] to either side. Normal velocities are in the upper [Formula: see text], but over the interval from [Formula: see text] below the seafloor at the northeast side, the velocities are higher than the average normal slope sediment velocity of approximately [Formula: see text]. These high velocities are probably related to the high reflectivity zone and to the bottom portion of the massive hydrate detected by resistivity measurements in the upper [Formula: see text] at U1328.

Effects of Ca-enrichment on authigenic carbonate formation at cold vent sites off Costa Rica: a numerical model approach

The Costa Rican forearc is characterized by active fluid venting related to mud diapirism and volcanism. The geochemical compositions of fluids obtained from dewatering sites indicate that mineral precipitation or dehydration is the major driver of fluid mobilization and upward migration. The peculiar situation at the latter sites is that Ca concentrations in the upward migrating fluids are well above seawater levels. In turn, these Ca-enriched fluids could offer a potential reason for widespread carbonate caps on top of the mounds.