Extensive Hydrate Research Articles

Upward migration of the shallow gas enhances the production behavior from the vertical heterogeneous hydrate-bearing marine sediments

Low gas production rates and insufficient gas yield hinder the large-scale production from natural gas hydrates; a joint production of gas hydrate and its underlying shallow gas is expected to address this limitation. This study focuses on the interaction between heterogeneous hydrate reservoirs and the upward migration of the shallow gas. The results indicated a 38.4 % increase in production efficiency with the assistance of the shallow gas. Specially, the melt water generated from extensive hydrate decomposition could potentially induce a lateral migration of the shallow gas at the interfacial zones of the heterogeneous reservoirs. Further investigation revealed that a lower production pressure would help the release of the shallow gas as well as the hydrate decomposition, thereby contributing to a 64.55 % shorter t90. A faster depressurization rate could facilitate the temperature recovery by intensifying the lateral movement of the shallow gas in the junction layer. Consequently, a proper control of the upward channeling of the shallow gas was suggested in the field test for a successive and secure gas production. Our results could be of help in elucidating the interlayer interference mechanisms and the selection of the depressurization strategy for a better recovery efficiency from the multi-gas source reservoirs.

Investigation on Hydrate Formation and Growth Characteristics in Dissolved Asphaltene-Containing Water-In-Oil Emulsion.

Clarifying the effect of asphaltene on hydrate formation and growth is of great significance to the operation safety in deepwater petroleum fields. To investigate the influence of low-concentration dissolved asphaltenes on the formation kinetics and growth process of hydrates in water-in-oil emulsions, experiments with asphaltene concentrations ranging from 50 to 1000 ppm were carried out using a high-pressure visual reactor. At a low concentration, the adsorption of asphaltene monomers on the oil-water interface or nanoaggregates in the bulk barely affected the nucleation of hydrate and the induction time of hydrate formation. However, it would hinder the microscopic mass transfer process and heat transfer process between gas molecules and then mitigate the initial rate of hydrate formation. Therefore, the dissolved asphaltenes could not be used as antiagglomerants (AAs) to efficiently inhibit the aggregation of hydrate particles at low concentrations under our experimental conditions, causing extensive hydrate agglomeration and deposition in the reactor.

Crustal processes sustain Arctic abiotic gas hydrate and fluid flow systems

The Svyatogor Ridge and surroundings, located on the sediment-covered western flank of the Northern Knipovich Ridge, host extensive gas hydrate and related fluid flow systems. The fluid flow system here manifests in the upper sedimentary sequence as gas hydrates and free gas, indicated by bottom simulating reflections (BSRs) and amplitude anomalies. Using 2D seismic lines and bathymetric data, we map tectonic features such as faults, crustal highs, and indicators of fluid flow processes. Results indicate a strong correlation between crustal faults, crustal highs and fluid accumulations in the overlying sediments, as well as an increase in geothermal gradient over crustal faults. We conclude here that gas generated during the serpentinization of exhumed mantle rocks drive the extensive occurrence of gas hydrate and fluid flow systems in the region and transform faults act as an additional major pathway for fluid circulation.

PCATS triaxial testing: Geomechanical properties of sediments from pressure cores recovered from the Bay of Bengal during expedition NGHP-02

Abstract The Indian National Gas Hydrate Program Expedition 02 (NGHP-02) was the most comprehensive gas hydrate drilling expedition carried out to date. From 74 pressure cores that were successfully recovered from various site locations offshore India, 19 subsamples were obtained for further detailed geotechnical analysis using the PCATS Triaxial apparatus to investigate the geomechanical behaviour of the cores, including small-strain stiffness, Gmax, undrained shear strength, Su, as well as direct-flow measurements of permeability, k. Samples tested included fine-grained muds with no appreciable hydrate through to coarse-grained sands that contained extensive hydrate within the pore space. Although the subsampling and transfer of pressure cores into the PCATS Triaxial under zero effective confining stress, σ′, remains challenging, 12 samples were successfully transferred and underwent detailed geotechnical characterization. During consolidation, after reapplication of in-situ σ′, all samples experienced axial and radial consolidation, with variations between samples seemingly dependent on the degree of sample disturbance, stress relaxation between coring and testing, hydrate saturation, Sh and grain size, D50. The largest values of Gmax were obtained from samples with high Sh in the pore space, with values much higher than that expected for similar sediments without hydrate under comparable σ’. Samples with high permeability had both high Sh and larger grain size, suggesting that in coarse-grained sediments sufficient pathways are available for reasonable fluid flow even with high hydrate saturations. Triaxial testing and unconfined compression tests highlighted the influence of hydrate on increasing sediment strength, although the size of the sediment grains appeared to have an important control on the magnitude of the strength increase and the overall stress-strain behaviour. The results from the detailed geotechnical characterization of the recovered pressure cores will be invaluable in helping India identify potential locations for future gas production wells, and assess the long-term performance of such reservoirs.

WITHDRAWN: Three-dimensional seismic evidence of extensive gas hydrate deposits linked with large free gas columns suggests long-range advection mechanisms

The mechanisms associated with the accumulation of natural gas hydrates in coarse-grained sediments are largely unconstrained. An improved understanding of such processes is crucial to efficiently prospect for hydrate resources. Therefore, we use three-dimensional seismic imaging to reveal amplitude patterns reflecting extensive hydrate deposits along dipping layers in the deepwater frontal anticlines of the Guajira Basin (offshore Northern Colombia). These gas hydrate-bearing sediments have a seismic character that is highly diagnostic for elevated saturations (>50%) in sand-rich lithologies, being expressed as segments of enhanced stratigraphic reflections, comparable in amplitude but opposite in polarity to the reflections observed in the underlying free gas zone. Observations in seismic sections and amplitude maps of a bottom-simulating reflection and key horizons indicate that the distribution of hydrates and free gas is largely affected by the structural setting of the study area, where hydrates and free gas further have markedly diverse extents in different anticlines. We recognise a link between hydrates and free gas, such that the most extensive hydrate accumulations and the largest (up to 570 m) free gas columns occur along the same dipping horizons, cross-cutting the base of gas hydrate stability. These observations suggest that a long-range advection of free gas operates with varying effectiveness in these structures. We hypothesise that these hydrate deposits form by overpressure-controlled pulses of free gas invasion into the gas hydrate stability zone along dipping stratal conduits. This process implies that hydrate-bearing sediments constitute an efficient but dynamic membrane seal for large buoyant free gas columns. This coupling between free gas and hydrate accumulations represents an extraordinary example of hydrate distribution governed by advective processes illustrated in three dimensions.

How good are the crystallisation methods for co-crystals? A comparative study of piroxicam

Co-crystallisation of two components into one crystal form can enhance the solid-state properties of drug compounds. A plethora of crystallisation methods has been applied to co-crystallisation and the reported study compares the three most common ones (crystallisation from the melt, from solution and solvent-drop grinding) with respect to their applicability and necessity for a co-crystal screening. Piroxicam, a non-steroidal anti-inflammatory drug, was chosen as a model system and submitted to an extensive co-crystal screening using twenty different acids as co-crystal formers, six crystallisation techniques and five solvents. A total of 46 co-crystal forms were obtained, 38 of which are novel. Solvent-drop grinding showed the highest absolute number of experiments resulting in co-crystals, while crystallisation from the melt yielded the highest number of co-crystal formation when crystalline material was obtained. Evaporation resulted in a high number of crystalline products but many of those were binary and ternary mixtures of crystal forms. Cooling and precipitation techniques gave only poor results. Acetone and THF showed the highest number of crystalline products while chloroform gave the highest relative yield of co-crystals. Ethanol and acetonitrile showed extensive hydrate formation. No influence of the co-crystal former on the co-crystal formation could be detected.

Enhanced growth of methane–propane clathrate hydrate crystals with sodium dodecyl sulfate, sodium tetradecyl sulfate, and sodium hexadecyl sulfate surfactants

In the present study the effect of three commercially available anionic surfactants on the hydrate growth from a gas mixture of 90.5 mol% methane/9.5 mol% propane mixture was investigated. The surfactants used were sodium dodecyl sulfate (SDS), sodium tetradecyl sulfate (STS), and sodium hexadecyl sulfate (SHS). The morphology of the growing crystals and the gas consumption were observed during the experiments. The results showed that in the presence of surfactants, branches of porous fibre-like crystals were formed instead of dendritic crystals formed in the absence of any additive. In addition, extensive hydrate crystal growth on the crystallizer walls and a “mushy” hydrate layer instead of a thin crystal film appeared at the gas/water interface. Finally, the addition of SDS with concentration range between 242 and 2200 ppm (Δ T=13.1 K) was found to increase the mole consumption for hydrate formation by approximately 14 times compared to pure water. This increase is related to the change in hydrate morphology, whereby a more porous hydrate forms with enhanced water/gas contacts.

Methane–ethane and methane–propane hydrate formation and decomposition on water droplets

Gas hydrate formation and decomposition on water droplets using an 89.4% methane—10.6% ethane mixture, and a 90.1% methane—9.9% propane mixture were carried out in a new apparatus suitable for morphology studies. As expected the induction time was found to be much shorter when the water had hydrate memory. All droplets nucleated simultaneously and the droplet size and shape had no noticeable effect on induction time and macroscopic crystal growth morphology for hydrates from the methane–ethane mixture. However, the surface of the hydrate crystals from methane–propane had a “hairy-like” appearance which changed to a smooth surface over time. Moreover, the smaller droplets during hydrate reformation showed an extensive hydrate growth and looked like snow-flakes. Sequential pictures generated by time-lapse videos showed that the time required for hydrate to cover the water droplet surface ranged from 10 to 23 s and was shorter when there was gas-phase agitation (mixing). The growth is postulated to occur in two stages. The first stage lasts about 10–23 s and growth takes place laterally. Growth takes place at the hydrate/gas and the hydrate/water interfaces during the second stage. The implication of the findings for process design of hydrate formation vessels is also discussed.

Uptake and Reaction of ClONO2on Water Ice and HCl Trihydrate at Low Temperatures

Chlorine nitrate adsorption kinetics and uptake have been measured on ordered ice and HCl trihydrate films at temperatures below 150 K. Reaction was followed using a thermal molecular beam, with mass spectrometric detection of gas-phase products and temperature-programmed desorption (TPD) and IR to identify adsorbed species. The sticking probability (S) on pure water ice is (0.98 ± 0.03) at 85 K and remains near unity for temperatures up to 145 K. Initially S is independent of the ClONO2 uptake, indicating a trapping mechanism for reaction. A molecular state which desorbs near 120 K during TPD is identified as a precursor state and above this temperature molecular ClONO2 is not stable on the surface and adsorption forms HOCl and nitric acid hydrate. On a clean ice surface the reaction probability starts to decrease after 0.1 monolayer of ClONO2 has adsorbed, reaction ceasing (S < 5 × 10-2) at an uptake of (0.25 ± 0.05) monolayer, independent of temperature. Reaction occurs even at low temperature, where the surface is immobile, indicating that ClONO2 hydration can occur on the ice surface and does not require an extensive hydrate cage. The saturation stoichiometry is consistent with a surface covered with HOCl and an amorphous nitric acid trihydrate film. The initial reaction probability for ClONO2 uptake onto pure HCl trihydrate films was similar, (0.98 ± 0.05) for temperatures between 85 and 145 K with some chlorine desorbing promptly into the gas phase even at 85 K. The uptake of ClONO2 increases from 0.5 to ca. 1 monolayer above 125 K, the temperature at which HCl starts to transport into water ice films, reaction extending beyond the top layer of the HCl trihydrate surface.

Geothermal conditions for gas hydrate stability in the Beaufort-Mackenzie area: the global change aspect

Gases locked in hydrates or trapped beneath a gas hydrate cap within the earth are potential contributors to the greenhouse effect, and therefore both thermal conditions of and occurrences of the methane hydrates should be considered in the study of past climate change and of future global warming. The decomposition of methane hydrates triggered by an increase in near surface temperatures and the subsequent upward migration of released gases is occurring at present in the Beauffort-Mackenzie area of northern Canada. In addition to surface warming, the warming effect of the upward flow of the deep fluids, recharged in high elevation areas bordering the Alaska and Yukon coastal plain, may also be a factor in the release of methane directly from deeper buried hydrates in the fluid discharge zones. Any assessment of the total methane contribution to the atmosphere and the rate of the release requires a knowledge of the distribution, spatially and with depth, the temperature and composition of the gas hydrates. In this study the zones of methane hydrate stability are predicted by a thermal method and compared with the distribution of hydrates detected on well logs. An extensive hydrate prone layer extending to as deep as 1400±200 m over an area of 50,000 km 2 is predicted by the thermal data and hydrate stability field. Comparison of the predicted maximum depths of methane hydrate stability with the maximum depths of hydrate occurrences in 52 wells shows general agreement in the areas of thick offshore and onshore permafrost. Differences in several areas of up to 400 m between the thermally predicted hydrate base and the deepest detected hydrates (detected hydrates are deeper than the predicted ones) can be explained by changes in gas composition. Otherwise low near-surface thermal gradients of approximately 15 mK/m to 20 mK/m (in comparison with observed deep thermal gradients of 25–40 mK/m) would be needed to explain the existence of deep hydrates in the area of the southern Mackenzie Delta trough and offshore north of 71° N latitude. Unfortunately there is no reliable industrial temperature observation from wells to support the latter. Such regional studies of the distribution of gas hydrates, including the stability of those deposits, form a crucial component of an assessment of the influence of gas hydrate formation and decomposition on the proportion of methane present in the earth's atmosphere. Current estimates suggest that between 10.E18 and 10.E21 tonnes of methane may be presently locked in gas hydrate deposits. To fully assess the total amount and the potential contribution to global warming, similar regional assessments are needed for each of the major areas of occurrence, especially in the circumpolar regions which are subject to the greatest increase in temperature conditions.

Geothermal conditions for gas hydrate stability in the Beaufort-Mackenzie area: the global change aspect

Gases locked in hydrates or trapped beneath a gas hydrate cap within the earth are potential contributors to the greenhouse effect, and therefore both thermal conditions of and occurrences of the methane hydrates should be considered in the study of past climate change and of future global warming. The decomposition of methane hydrates triggered by an increase in near surface temperatures and the subsequent upward migration of released gases is occurring at present in the Beauffort-Mackenzie area of northern Canada. In addition to surface warming, the warming effect of the upward flow of the deep fluids, recharged in high elevation areas bordering the Alaska and Yukon coastal plain, may also be a factor in the release of methane directly from deeper buried hydrates in the fluid discharge zones. Any assessment of the total methane contribution to the atmosphere and the rate of the release requires a knowledge of the distribution, spatially and with depth, the temperature and composition of the gas hydrates. In this study the zones of methane hydrate stability are predicted by a thermal method and compared with the distribution of hydrates detected on well logs. An extensive hydrate prone layer extending to as deep as 1400±200 m over an area of 50,000 km 2 is predicted by the thermal data and hydrate stability field. Comparison of the predicted maximum depths of methane hydrate stability with the maximum depths of hydrate occurrences in 52 wells shows general agreement in the areas of thick offshore and onshore permafrost. Differences in several areas of up to 400 m between the thermally predicted hydrate base and the deepest detected hydrates (detected hydrates are deeper than the predicted ones) can be explained by changes in gas composition. Otherwise low near-surface thermal gradients of approximately 15 mK/m to 20 mK/m (in comparison with observed deep thermal gradients of 25–40 mK/m) would be needed to explain the existence of deep hydrates in the area of the southern Mackenzie Delta trough and offshore north of 71° N latitude. Unfortunately there is no reliable industrial temperature observation from wells to support the latter. Such regional studies of the distribution of gas hydrates, including the stability of those deposits, form a crucial component of an assessment of the influence of gas hydrate formation and decomposition on the proportion of methane present in the earth's atmosphere. Current estimates suggest that between 10.E18 and 10.E21 tonnes of methane may be presently locked in gas hydrate deposits. To fully assess the total amount and the potential contribution to global warming, similar regional assessments are needed for each of the major areas of occurrence, especially in the circumpolar regions which are subject to the greatest increase in temperature conditions.

Extensive Hydrate Formation of 5-Nitrofurfural in Neutral Aqueous Solutions: Implications for Its Reactivity

Extensive Hydrate Formation of 5-Nitrofurfural in Neutral Aqueous Solutions: Implications for Its Reactivity