The kinetic inhibitor Poly Vinyl Caprolactam (PVCap) was added as a kinetic inhibitor to the gas-water system. Different hydrate formers were used in order to obtain formation of the different hydrate structures (sI, sII and sH). All hydrate structures were formed with PVCap. The effect of applying different melting rates was investigated. The isochoric technique was used to obtain dissociation temperatures and corresponding pressures. The melting rate was found to be a parameter influencial for the dissociation temperature. Even for very slow melting rates such as 0.0125 Kelvin per hour, the final dissociation temperature was significantly higher that the dissociation temperature for the corresponding non-inhibited system.

Except for direct drilling and sampling of marine gas hydrates, the occurrence of gas hydrates has been identified generally by inference from indirect evidence, derived from geological, geophysical, and geochemical data. In this paper, we intend to discuss the geochemical anomalies of pore waters and their implications for gas hydrate occurrence in the northern continental slope of the South China Sea. The molecular concentration and isotopic composition of methane in sediments can provide clues to gas sources, whereas ionic and isotopic compositions of pore waters, such as steep SO42- gradients, shallow SMI (sulfate-methane interface) depths; decreasing pore water chlorinity, and heavy oxygen isotopic compositions, are used to identify gas hydrate occurrence and the distribution and thickness of sediment layers containing gas hydrates. Other good geochemical indicators include anions and cations concentrations such as Br-, I-, PO43-, NH4+, Ca2+, Mg2+, Sr2+, B3+, Li+, and Ba2+ in pore waters. We also found that the very negative carbon isotopic compositions of dissolve inorganic carbon (DIC) in pore waters can serve as good indicators for gas hydrate occurrence. In the South China Sea, three most promising target areas for gas hydrates include the Dongsha, Shenhu, and Xisha Trough.

The northern margin of South China Sea contains several favorable areas for occurrence of gas hydrate. In this study, we collected pore water samples in two piston cores (X-01 and D-01) from Xisha Trough and Dongsha area, respectively, and the concentrations of sulfate and carbon isotopic compositions of dissolved inorganic carbon (DIC) were measured. The results showed different geochemical characteristics in these two sites. The X-01 core shows relatively constant δ13C-DIC values and sulfate concentrations, which suggest that anaerobic methane oxidation (AMO) processes did not occur in this site. In contrast, very large variation in δ13C-DIC values and sulfate concentrations are revealed in D-01 core, and good linear correlations for sulfate gradients and δ13C-DIC values are observed. The calculated sulfate-methane interface (SMI) depth is 9.6 mbsf. These data indicate that an AMO process occurred in sediments with large methane flux from depth in the Dongsha area, which are comparable to other gas hydrate locations in the world oceans such as the Blake Ridge. We suggest that the Dongsha area is one of the most favorable targets for future gas hydrate exploration.

Understanding the deep biosphere is of great commercial and scientific interest and will contri-bute to increased knowledge of the environment. If environmentally relevant results are to be ob-tained the precondition to achieve genuine findings is research in pristine habitat as close as pos-sible to those encountered in-situ. Therefore benthic conditions of sediment structure and gas hydrates, temperature, pressure and bio-geochemistry have to be maintained during the sequences of sampling, retrieval, transfer, sto-rage and downstream analysis. At the Technische Universität Berlin (TUB) the Pressurized Core Sub-Sampling and Extrusion System (PRESS) was developed in the EU project HYACE/HYACINTH. It enables well-defined sectioning and transfer of drilled pressure-cores [obtained by HYACE Rotary Corer (HRC) and Fugro Pressure Corer (FPC)] into transportation and investigation chambers. Coupled with DeepIsoBUG (University Cardiff, John Parkes) it allows sub-sampling and incubation of coaxial core-sections to examine high-pressure adapted bacteria or remote biogeochemical processes in defined research conditions of the laboratory; all sterile, anaerobic and without depressurisation. Appraisals of successful PRESS deployments in the Gulf of Mexico, on IODP Expedition 311 and as part of the NGHP expedition 01 demonstrate the general concept to be feasible and useful. Aided by Deutsche Forschungsgemeinschaft (DFG) TUB is currently working on concepts to downscale the system in order to reduce logistical and financial expenses and, likewise, to enlarge its implementation by requiring less operating space. Redesigning the cutting mechanism shall simultaneously adjust the system to harder cores (e.g., ICDP). Novel transportation chambers for processed sub-samples intend to make the system more attractive for a broad spectrum of users and reduce their interdependence.

In this work the nucleation kinetics of propane gas hydrate has been investigated experimentally using a stirred batch reactor. The experiments have been performed isothermally recording the pressure as a function of time. Experiments were conducted at different stirring rates, but in the same supersaturation region. The experiments showed that the gas dissolution rate rather than the induction time of propane hydrate is influenced by a change in the stirring rate. This was especially valid at high stirring rates when the water surface was severely disturbed. Addition of polyvinylpyrrolidone to the aqueous phase was found to reduce the gas dissolution rate slightly, however the induction times were prolonged quite substantially. The induction time data were correlated using a newly developed induction time model based on crystallization theory also capable of taking into account the presence of additives. In most cases reasonable agreement between the data and the model could be obtained. The results revealed that especially the effective surface energy between propane hydrate and water is likely to change when the stirring rate varies from very high to low. The prolongation of induction times according to the model is likely to be due to a change in the nuclei-substrate contact angle.

Occurrences of carbonate-cemented nodules and concretions exposed on the seafloor that contain cements with light carbon isotopes, indicating a contribution of methane-derived carbon, are commonly interpreted to be indicators of seafloor fluid venting. Thus, their presence is commonly used as an indicator of the possible occurrence of methane gas hydrate within the near subsurface. While some of these carbonates exhibit facies that require formation on the seafloor, the dominant fine-grained lithology associated with these carbonates indicates they were formed as sedimenthosted nodules within the subsurface and are similar to nodules that are obtained from the subsurface in Deep Sea Drilling Project, Ocean Drilling Project, and Integrated Ocean Drilling Project boreholes. Here we present the hypothesis that the occurrence of these carbonates on the seafloor may instead indicate areas of persistent seafloor erosion.

The chemical structure of polyether amines (PEA), mainly electron donating multiple oxygen and nitrogen atoms as well as active hydrogen atoms, make such compounds actively participating in the formation of hydrogen bonds with surrounding molecules. Hydrophobic polypropylene glycol functionality gives PEA's properties of multi-headed surfactants having hydrophilic amine groups. These groups have a strong affinity for water molecules, ice and hydrate crystals. Such PEA compounds have been known for several years. However, the hydrate inhibition properties of PEA’s were only discovered about twelve years ago. The first discovery stimulated more research in laboratories and led to practical applications for hydrate inhibition in gas fields. An interesting property of PEAs is their synergistic effect on hydrate inhibition when applied concurrently with polymeric kinetic hydrate inhibitors (KHI) or thermodynamic inhibitors (THI). The combination inhibitors are better inhibitors than a single component one. Quaternized polyether diamines are efficient antiagglomerant (AA) hydrate inhibitors while different derivatization can produce dual functionality compounds, i.e. corrosion inhibitors/gas hydrate inhibitors (CI/GHI). With all of this versatility, PEAs found application for hydrate inhibition in oil and gas fields onshore and offshore in production, flowlines and completion. The PEAs have an excellent record in protecting gas-producing wells from plugging with hydrates. (Final corrected copy of ICGH paper 5347)

The use of Kinetic Hydrate Inhibitors (KHI) is one of the optimum methods employed to control gas hydrate formation issues and provide flow assurance in oil and gas production systems. The application of this technology has several advantages to operators, including significant cost savings and extended life of oil and gas systems. This paper will highlight a specific case where a Major operator in the North Sea (UK sector) significantly reduced the cost of well intervention operations by applying a KHI in a subsea gas lift line. Considerable cost savings were realized by reducing volume of chemical required and this enabled the application to be performed from the FPSO eliminating the need for a dedicated Diving Support Vessel (DSV). Furthermore, the application of KHI also reduced manual handling and chemical logistics usually associated with this particular treatment. In order to prevent mineral scale deposition occurring in downhole tubing and near well bore and in the formation; scale inhibitor squeeze applications are standard practice. For subsea wells the fluids can be pumped down in to the well via gas lift lines. However, upon completion of previous scale squeeze operations at this particular location, hydrate formation was observed when a mixture of MEG and water was used following interventions via the gas lift line. By applying 1% KHI with a mixture of MEG and Water, the well was brought back into production following scale squeeze operations without hydrate formation occurring.

On the lower continental slope off Vancouver Island near scientific ocean drilling IODP Site U1326, traveltime modeling along several ocean bottom seismograph (OBS) profiles shows anomalous high velocities of about 2.0 km/s at 70 - 100 m depth (compared to a no-hydrate reference of about 1.6 km/s). These velocities are consistent with the Site U1326 downhole sonic logs that show velocities up to 2.8 km/s near these depths. The drillhole high velocities are interpreted as caused by nearly massive hydrate with concentrations as large as 60-80% of the pore space. The OBS seismic velocities show that high hydrate concentrations of at least 20-30% are laterally extensive out to distances of at least 6 km on either side of the drillhole. A grid of migrated single-channel data shows a sequence of 15- to 75-m-high seafloor scarps, cutting across the ridge perpendicular to the deformation front. These are interpreted as normal faults. Two of the largest fault scarps bound a prominent ~2.5-km-wide slump feature on the steep seaward slope of the frontal ridge. This provides strong evidence that the slump is fault-controlled, and the base of the slump is near the base of hydrate stability suggesting that the slumping is also related to the presence of gas hydrate. At IODP drill Site U1327 on the mid-continental slope, seismic data were recorded along a 1-km-long profile of 10 OBSs. Traveltimes from wide-angle and vertical-incidence arrivals were inverted simultaneously for velocity structure. Corresponding hydrate concentrations increase with depth with an average of about 15% in the 100-m-thick layer above the base of hydrate stability . The seismic structure shows that this local hydrate distribution extends on the kilometer-scale away from the drillhole, as also suggested by multichannel interval velocities in the region. At Site U1328 (Bullseye Vent), seismic images derived from the very high resolution deep-towed DTAGS reflection data show that the top of a zone of high reflectivity, 10-25 m in thickness, extends from the seafloor to a depth of ~30 m. This zone likely corresponds to the shallow region of massive methane hydrate detected in the upper 40 m in the drillhole, and may represent a system of fractures through which fluids and gas pass from the main vent to the seafloor.

Water column methane measurements have been used to understand both the global distribution of methane in the oceans and the local flux of methane from geologic sources on the continental margins, including methane vents and gas-hydrate-bearing sites. We have measured methane concentrations in 1607 water samples collected along the central California continental margin. Methane supersaturation of the surface mixed layer (0-50 msbsl) is widespread and above a well-defined subsurface particle maximum (~50 mbsl) that generally corresponds with the pycnocline. Local production of methane appears to be occurring in the surface mixed layer above the particle maximum and may not be particle-associated. Methane concentrations in water column CTD cast profiles and ROV-collected bottom waters obtained in Partington, Hueneme, Santa Monica, and Redondo submarine canyons increase towards the seafloor and are distinctly higher (up to 186 nM) compared to open-slope and shelf waters at similar depths. These values are in excess of measured surface water methane concentrations and could not be generated by mixing with surface water. Elevated methane concentrations in these submarine canyons and persistent mid-water methane anomalies in Ascension and Ano Nuevo Canyons could result from restricted circulation and/or proximity to gas vents, seafloor exposure of methane gas hydrates, recently-eroded methane-rich sediment, submarine discharge of methane-rich groundwater, or particle-associated methane production. On the Santa Barbara shelf water column methane profiles near known gas vents also increase in concentration with increasing depth. Thus, elevated bottom water methane concentrations observed in submarine canyons may not be diagnostic of proximity to methane vents and may be caused by other processes.