The statistics of liquid-to-crystal nucleation are measured for clathrate-forming mixtures of tetrahydrofuran and water using an automatic lag time apparatus (ALTA). We measure the nucleation temperature where a single sample is repeatedly cooled, nucleated and thawed. This is done for a series of tetrahydrofuran concentrations and in several different sample tubes since the nucleation is heterogeneous and occurring on the tube wall. The measurements are also done at the same concentrations and tubes but with an added catalyst, a single crystal of silver iodide. We discuss the need for this type of measurement if the true nucleation temperature of the clathrate is to be found. Comparisons are also made with our high pressure data on real-world clathrate formers.

Two internationally-partnered research well programs, in 1998 and 2002, studied the Mallik gas hydrate accumulation in the Mackenzie Delta, Canada. Gas hydrate bearing intervals were cored, logged and production tested thus establishing Mallik as an excellent site for testing geophysical imaging techniques. Here, we apply a model-based acoustic impedance inversion technique to 3D seismic reflection data acquired over the Mallik area to characterize gas hydrate occurrences and to help define their spatial extent away from well control. Sonic logs in Mallik research wells show that P-wave velocity of sediments increases with hydrate saturation, enough to produce detectable reflections for the lower two of three known gas hydrate zones. The inversion method converts these reflections into acoustic impedances from which velocity and hydrate saturation can be estimated. Acoustic impedance inversion results indicate that the deepest gas hydrate zone covers an area of approximately 900,000 m2. With some assumptions on the lateral continuity of gas hydrate saturation, porosity and thickness measured at the wells, we estimate that this zone contains approximately 771x106 m3 of gas at standard atmospheric pressure. At a regional scale, results allowed the detection of a high-velocity area near the A-06 well, about 6 km south-east of 5L-38. We infer that the high velocity area corresponds to a gas hydrate accumulation. Logging data in A-06 indicate the presence of gas hydrates in this area and support our interpretation.

Mineralogical and isotopic analysis of authigenic carbonates from different gas hydrate-bearing seepage structures in the Derugin Basin (Sea of Okhotsk) are presented. The analysis showed the existence of four morphological types of carbonates, with all of them mainly of Mg-calcite.13C values of carbonates generally light owing to the inheritance of carbon from microbial methane. 13C-enriched samples at the VNIIOkeangeologia structure with 13C values of up to +9.3‰ represent carbonate precipitation due to methanogenesis. The calculated equilibrium 18O values of carbonates in general correspond to measured values.

Large quantities of natural gas hydrate are present in marine sediments along the coastlines of many countries as well as in arctic regions. This research is aimed at assessing production of natural gas from the marine deposits. We had developed a multiphase, multicomponent, thermal, 3D simulator in the past, which can simulate production of hydrates both in equilibrium and kinetic modes. Four components (hydrate, methane, water and salt) and five phases (hydrate, gas, aqueous-phase, ice and salt precipitate) are considered in the simulator. In this work, we simulate depressurization and warm water flooding for hydrate production in a hydrate reservoir underlain by a water layer. Water flooding has been studied as a function of injection temperature, injection pressure and production pressure. For high injection temperature, the higher pressure increases the flow of warm water (heat) in the reservoir making the production rate faster, but if injection temperature is not high then only depressurization is the best method of production. At intermediate injection temperature, the production rate changes non-monotonically with the injection pressure.

Hundreds of pockmarks and mounds, which seismic reflection sections show to be underlain by chimney-like structures, exist in southeast part of the Vøring plateau, Norwegian continental margin. These chimneys may be representative of a class of feature of global importance for the escape of methane from beneath continental margins and for the provision of a habitat for the communities of chemosynthetic biota. Thinning of the time intervals between reflectors in the flanks of chimneys, observed on several high-resolution seismic sections, could be caused by the presence of higher velocity material such as hydrate or authigenic carbonate, which is abundant at the seabed in pockmarks in this area. Evidence for the presence of hydrate was obtained from cores at five locations visited by the Professor Logachev during TTR Cruise 16, Leg 3 in 2006. Two of these pockmarks, each about 300-m wide with active seeps within them, were the sites of high-resolution seismic experiments employing arrays of 4-component OBS (Ocean-Bottom Seismic recorders) with approximately 100-m separation to investigate the 3D variation in their structure and properties. Shot lines at 50-m spacing, run with mini-GI guns fired at 8-m intervals, provided dense seismic coverage of the sub-seabed structure. These were supplemented by MAK deep-tow 5-kHz profiles to provide very high-resolution detail of features within the top 1-40 m sub-seabed. Travel-time tomography has been used to detail the variation in Vp and Vs within and around the chimneys. Locally high-amplitude reflectors of negative polarity in the flanks of chimneys and scattering and attenuation within the interiors of the chimneys may be caused by the presence of free gas within the hydrate stability field. A large zone of free gas beneath the hydrate stability field, apparently feeding several pockmarks, is indicated by attenuation and velocity pull-down of reflectors.

In April-June of 2007, a gas hydrate drilling expedition was carried out by using M/V Bavenit in Shenhu Area, the north slope of South China Sea. High concentrations of hydrate (>40%) were obtained in a disseminated forms in foram-rich clay sediments at 3 selected sites. The hydrate-bearing sediments ranged several ten meters in thickness are located in the lower part of GHSZ, just above the BGHSZ, and are typically characteristic of higher sonic velocity and resistivity, and lower gamma density in wireline logging profiles. Evidences for gas hydrate include the IR cold spots and temperature anomalies, salinity and chlorite geochemical anomaly of pore water for non-pressurized cores, and X-ray imaging, high p-wave velocity and low gamma density, and high concentration of methane from the pressurized cores. Gasses are mainly methane (max. ethane 0.2-0.3%), therefore only hydrate S1 is formed. It is inferred that the foram content and other silt size grains may provide enough free water for the hydrate to happily occupy both the large spaces in the forams and for it to distribute itself evenly (disseminated) throughout the formation. It is possible that all the forams are hydrate filled. As the forams are visible does this not count for visible white gas hydrates.

Differential scanning calorimetry has been used to study the kinetics of formation of clathrate hydrates in the systems water-CCl3F and water-CH4, in which the water phase was dispersed in an oil phase in the form of an emulsion. CCl3F hydrates were formed at ambient pressure and constant temperatures of -10, -15 and -20 °C. The results showed that the crystallization of both ice and hydrate are in competition at the lowest temperature, whereas only hydrate is formed at -10 or -15 °C. CH4 hydrates were studied using a high-pressure DSC in the range 10 to 40 MPa, at various temperatures. At high driving force, the heat peak related to the formation of hydrates has a regular and symmetric shape, and its height and width depend on the gas pressure and sub cooling degree. At near equilibrium conditions, hydrate formation can be delayed by several hours, but is still clearly observable. A model based on crystal growth theory coupled with a statistical law to take into account the germination in micro sized droplets is proposed.

While alternative natural gas transportation technologies against currently available pipeline or liquefied natural gas (LNG) are expected to develop to be suitable for small and medium or remote gas fields, Mitsui Engineering & Shipbuilding Co., Ltd. (MES) has been studying natural gas hydrate (NGH) transportation chain and advocated at ICGH2005 the NGH chain was economical compared with conventional LNG system under some conditions. Meanwhile, MES has been carrying out research and development on the relevant technology development including construction of 600 kg/day class NGH production and pelletizing plants and a re-gasification facility and the process technology resulted from this R&D leads to the forthcoming demonstration plant of 5 ton/day production (under construction) to be dedicated to the demonstration project of small-lot NGH land transportation in western Japan. As the latest achievement, MES and Mitsui & Co., Ltd. (Mitsui) established NGH Japan Co., Ltd. (NGHJ) in April 2007, in order to study in detail on actual viability of NGH ocean transportation chain. NGHJ, MES and Mitsui have been conducting a practical feasibility study on certain cases in Southeast Asia in cooperation with 6 Japanese leading companies related to natural gas businesses. The study suggests that NGH chain was appropriate as a media for transportation from Southeast Asia to Japan and regional transportation within Southeast Asia in view of economics.

This work deals with the problem of pipeline plugging by gas hydrates during oil production. Gas hydrates are crystals resulting from water and gas molecules association under high pressure and low temperature conditions. Such thermodynamical conditions are generally encountered during oil production and transport, particularly in deep offshore fields or in cold areas. Due to an agglomeration process which is still debated, hydrate occurrence can lead to plug formation. This study aims at improving the understanding in this mechanism process, in the case of water-in-oil emulsions. Therefore, ice or hydrate particle agglomeration is compared. Ice or trichlorofluoromethane (CCl3F) hydrate particles dispersed in xylene with asphaltenes as surfactant is chosen as a model system. As CCl3F hydrates are stable under atmospheric pressure, it allows us to apply different techniques without being limited by high pressure conditions. The Nuclear Magnetic Resonance (NMR) technique is used. The very different relaxation rate for solids or liquids is used to monitor in situ the ratio between solid and total hydrogen or fluorine as a function of time with controlled shearing conditions. Thus, a kinetic study is realized, that enabled to know the amount of ice formed. The apparent viscosity of the system, during crystallization and plugging, is also followed with rheometry in order to characterize agglomeration. This experimental approach allows us to highlight that physico-chemistry of interface water/oil has an important role in agglomeration. It enables us to discuss different mechanisms of agglomeration of ice and hydrate particles in a hydrocarbon phase.

Gas hydrates are ice-like crystalline solids composed of a hydrogen bonded water lattice entrapping low-molecular weighted gas molecules commonly of methane. These form under conditions of relative high pressure and low temperature, when the gas concentration exceeds those which can be held in solution, both in marine and on-land permafrost sediments. Simulating the mechanisms leading to natural gas hydrate emplacement in geological environments requires the modeling of the temperature, the pressure, the chemical reactions, and the convective/diffusive flow of the reactive species. In this study, we take into account the distribution of dissolved methane, methane gas, methane hydrate, and seawater, while ice and water vapor are neglected. The starting equations are those of the conservation of the transport of momentum (Darcy’s law), energy (heat balance of the passive sediments and active reactive species), and mass. These constitutive equations are then integrated into a 2-dimentional finite element in space, finite-difference in time scheme. In this study, we are able to examine the formation and distribution of methane hydrate and free gas in a simple geologic framework, with respect to geothermal gradient, dewatering and fluid flow, the methane in-situ production and basal flux. The temperature and pressure fields are mildly affected by the hydrate emplacement. The most critical parameter in the model appears to be the methane (L+G) and hydrate (L+G+H) solubility: the decrease in methane solubility beneath the base of the hydrate stability zone (BHSZ) critically impacts on the presence of free gas at the base of the BHSZ (thus the presence of a BSR), while the sharp decrease of hydrate solubility above the BHSZ up to the sea bottom critically impact on the amount of methane available for hydrate emplacement and methane seep into the water column.