Gas Hydrate Reserves Research Articles

Evaluation of rheological properties of guar gum-based fracturing fluids enhanced with hydroxyl group bearing thermodynamic hydrate inhibitors.

Naturally occurring gas clathrates are a significant methane resource-the primary component of natural gas, regarded as the cleanest hydrocarbon and a key feedstock for producing gray and blue hydrogen. Despite the global abundance of gas hydrate reserves, extraction via depressurization has yet to achieve commercially viable production rates. The primary limitation lies in the low permeability of hydrate-bearing sediments, where solid clathrates obstruct porous pathways, hindering dissociation and slowing gas recovery. Hydraulic fracturing has emerged as a promising technique to enhance conductivity, with initial studies indicating substantial increases in production rates when stimulation is applied. This study investigates the integration of thermodynamic hydrate inhibitors (THIs), such as methanol and polyethylene glycol 200 (PEG-200), into conventional polymer-based linear and crosslinked fracturing gels to improve performance. By targeting both rock and the embedded gas hydrates, these inhibitor integrated fracturing gels aim to facilitate faster fracture propagation and accelerate hydrate dissociation. The rheological performance of THI-integrated gels at varying concentrations is analysed, crucial for fracture formation, propagation, and proppant transport efficiency. Additionally, microscopic observations of additive interactions followed by fluid disintegration according to time are compared to evaluate residue formation and long-term integrity. Results indicate that methanol slightly increased the viscosity of linear gels at low concentrations and improved stability, reducing residue and slowing degradation, while higher concentrations required additional polymerizing agents to maintain performance. PEG-200 enhanced viscosity and stability in guar-based gels at low concentrations but caused shear-thinning at higher levels, limiting its suitability for high-viscosity operations. Crosslinked gels demonstrated superior proppant suspension and stability, generating less sediment-damaging residue compared to linear gels, with methanol further enhancing performance. Optimized integration of PEG-200 during borate crosslinking is critical, as higher concentrations risk premature gel degradation.

Research on Key Parameters of Wellbore Stability for Horizontal Drilling in Offshore Hydrate Reservoirs

The South China Sea has abundant reserves of natural gas hydrates, and if developed effectively, it can greatly alleviate the pressure on the energy supply in China. But the hydrate reservoirs in the sea area are loose, shallow, porous, and have poor mechanical properties. During the drilling process, the invasion of drilling fluid into this kind of reservoir is likely to induce mass decomposition of gas hydrate and, in turn, a significant reduction in mechanical strength around the wellbore as well as instability of the wellbore. In this study, in light of the engineering background of exploratory wells at the South China Sea, a temperature and pressure field model in a gas hydrate reservoir at sea during open circuit drilling was established, and then, based on this model, a comprehensive model for the stability analysis of the well drilled in the hydrate reservoir at sea was constructed, both of them with errors of less than 10%. With these two models, the effects of different drilling parameters on wellbore stability were investigated. The gas and liquid produced by the decomposition of hydrates in the formation will increase the pore pressure in the formation, thereby reducing the effective stress in the formation. The closer the formation is to the wellbore, the more thorough the decomposition of hydrates in the formation and the greater the effective plastic strain. Keeping all other conditions constant, the increase in drilling fluid invasion pressure and temperature, as well as reservoir permeability, will lead to a decrease in the mechanical strength of the formation around the wellbore and an expansion of the wellbore yield zone. The results can provide a theoretical reference for the stability analysis at sea.

Research on Lateral Load Bearing Characteristics of Deepwater Drilling Conductor Suction Pile

The vast reserves of natural gas hydrates in offshore areas present significant challenges to development. Surface well construction technology is crucial for the extraction of deepwater natural gas hydrates. To ensure the safety of the subsea wellhead during the drilling process for deepwater natural gas hydrates, a novel conductor suction pile device has been designed, comprising a combination of suction piles and surface conductors. And research has been conducted to investigate the lateral stability characteristics of the conductor suction pile. Drawing upon the pile foundation load-bearing theory and the equilibrium of the differential element, a theoretical analysis model and corresponding governing equations of the conductor suction pile system are established. A solution for a multi-point boundary value problem by simplifying the conductor suction pile system into a two-end free beam is proposed. The governing equations are then converted into a first-order differential equation system, and the four-stage Lobatto IIIa collocation method program for the multi-point boundary value problem is developed and resolved using MATLAB 2023a. Furthermore, a case study of a well in the South China Sea elucidates the effects of wellhead load and seabed soil properties on the lateral load-bearing capacity of the conductor suction pile system, verifying the collocation method’s validity against the results from the finite difference method. After conducting a comparative analysis of the lateral load-bearing performance between conductor suction piles and traditional surface conductors, it is observed that conductor suction piles exhibit lower horizontal displacement and bending moments compared to surface conductors. Therefore, conductor suction piles demonstrate a substantial safety margin. The research findings provide a theoretical basis for the lateral stability of conductor suction piles during deepwater natural gas hydrate drilling. This offers a safe and efficient method for surface well construction in the extraction of natural gas hydrates.

Numerical Simulation of Coastal Sub-Permafrost Gas Hydrate Formation in the Mackenzie Delta, Canadian Arctic

The Mackenzie Delta (MD) is a permafrost-bearing region along the coasts of the Canadian Arctic which exhibits high sub-permafrost gas hydrate (GH) reserves. The GH occurring at the Mallik site in the MD is dominated by thermogenic methane (CH4), which migrated from deep conventional hydrocarbon reservoirs, very likely through the present fault systems. Therefore, it is assumed that fluid flow transports dissolved CH4 upward and out of the deeper overpressurized reservoirs via the existing polygonal fault system and then forms the GH accumulations in the Kugmallit–Mackenzie Bay Sequences. We investigate the feasibility of this mechanism with a thermo–hydraulic–chemical numerical model, representing a cross section of the Mallik site. We present the first simulations that consider permafrost formation and thawing, as well as the formation of GH accumulations sourced from the upward migrating CH4-rich formation fluid. The simulation results show that temperature distribution, as well as the thickness and base of the ice-bearing permafrost are consistent with corresponding field observations. The primary driver for the spatial GH distribution is the permeability of the host sediments. Thus, the hypothesis on GH formation by dissolved CH4 originating from deeper geological reservoirs is successfully validated. Furthermore, our results demonstrate that the permafrost has been substantially heated to 0.8–1.3 °C, triggered by the global temperature increase of about 0.44 °C and further enhanced by the Arctic Amplification effect at the Mallik site from the early 1970s to the mid-2000s.

Low Temperature rheological characterization of single-step silica nanofluids: An additive in refrigeration and gas hydrate drilling applications

Silica nanofluids are novel interdisciplinary solutions that have found several industrial applications on account of their superior rheological, chemical, and mass/heat transfer properties. However, their use in low-temperature applications (primarily drilling through gas hydrate reserves) is constrained due to the lack of understanding of their rheological behavior under low-temperature and high-pressure conditions. Hence, in this study, the viscosity, and the stability of novel single-step silica nanofluids of varying composition (0.1–1 wt%, synthesized via the Stober sol-gel method) were investigated under 2–30 °C. Following a comprehensive analysis, it was observed that while increasing the concentration of silica NPs in the aqueous solution and reducing the temperature caused a slight increase in the viscosity of the solution, increasing pressure (till 50 bar) was found to have no appreciable effect on the viscosity of the solution. The silica nanofluids showed a characteristically vicious nature (higher values of G″ than G′). The nanofluids were also able to maintain their dispersion stability and did not show any sedimentation after repeated heating and cooling between 2 and 30 °C. Finally, the silica nanofluids were used as additives in water-based drilling fluids for drilling through gas hydrate reservoirs which are prone to having high gas influxes. The presence of silica NPs was able to stabilize the absorbed gas bubbles, reducing the likelihood of them affecting the mud returns and causing a runaway gas blowout, though the duration of gas bubble retention reduced significantly at a higher temperature. The observations of the study indicate the superior viability of formulated single-step silica nanofluids for low-temperature applications like refrigeration and gas hydrate drilling mud additives. • Nanofluid exhibited stable viscoelastic response at low temperature and high pressure. • Reducing temperature increased nanofluid viscosity but pressure had no appreciable effect. • Nanofluid exhibited dispersion stability after 300 heating-cooling cycles. • Nanofluid inclusion in drilling mud controlled rate of gas invasion for wellbore stability. • Proposal of using silica nanofluids in refrigeration and gas hydrate drilling applications.

Experimental study of frozen gas hydrate decomposition towards gas recovery from permafrost hydrate deposits below freezing point

Enormous natural gas hydrate reserves have been identified in the global permafrost and oceanic regions. How the existence of ice influences the hydrate dissociation is a fundamental issue related to the development of the permafrost-associated gas hydrate resources. The dissociation behaviors of frozen methane hydrate in hydrate-ice-gas saturated porous media below freezing point are studied in a high pressure reactor. The hydrate-bearing permafrost layer is simulated through decreasing the temperature of the methane hydrate samples to −0.60 °C, and then they are safely dissociated by depressurization and thermal stimulation. Results show that the disturbance on gas and water in the pores can induce secondary hydrate formation during the cooling of the system. The gas recovery rate by depressurization below freezing point is extremely slow, which is caused by the obstructive effect of ice on the diffusion of methane molecules. The self-preservation of frozen gas hydrate could be effectively broken under wellbore heating. Heat is primarily transferred by conduction mode across the hydrate and ice particles. The solid ice tends to absorb heat first and then melts into liquid water. The dissociated fluids play a role in promoting the heat transfer through thermal convection. Moreover, the net energy gain is found to be much higher than the energy consumption, and desirable energy efficiency has been obtained. Sensitivity analyses indicate that higher heat injection rate and lower ice saturation will be more favorable for the exploitation, while the production pressure seems to have negligible influence on the overall production efficiency.

Investigation of the hydrate reservoir production under different depressurization modes

Large reserves of natural gas hydrates exist, and the depressurization method has the greatest potential for gas hydrate reservoir recovery. Currently, the most commonly adopted depressurization simulation method is a constant bottom-hole pressure production scheme. This study proposes a new depressurization mode with decreasing bottom-hole pressure. The production characteristic was numerically investigated using this method. The results show the following: (1) As the depressurization exponent (n) decreases, the development effect improves, and production indexes including cumulative gas production/dissociation and gas-water ratio increase. However, the reservoir energy consumption is higher and the hydrate reformation is more severe. (2) Compared to the proposed depressurization mode, the hydrate production index of the constant bottom-hole pressure production (n = 0) is better. However, the hydrate reservoir energy consumption is higher and the hydrate reformation is more severe using constant bottom-hole pressure production. (3) To achieve a balance between production and reservoir energy consumption during depressurization production, the bottom-hole pressure should be controlled by selecting a suitable depressurization exponent between nmin and nmax, which can be determined through numerical simulations.

Investigation on the effect of oxalic acid, succinic acid and aspartic acid on the gas hydrate formation kinetics

Gas hydrate reserves are potential source of clean energy having low molecular weight hydrocarbons trapped in water cages. In this work, we report how organic compounds of different chain lengths and hydrophilicities when used in small concentration may modify hydrate growth and either act as hydrate inhibitors or promoters. Hydrate promoters foster the hydrate growth kinetics and are used in novel applications such as methane storage as solidified natural gas, desalination of sea water and gas separation. On the other hand, gas hydrate inhibitors are used in oil and gas pipelines to alter the rate at which gas hydrate nucleates and grows. Inhibitors such as methanol and ethanol which form strong hydrogen bond with water have been traditionally used as hydrate inhibitors. However, due to relatively high volatility a significant portion of these inhibitors ends up in gas stream and brings further complexity to the safe transportation of natural gas. In this study, organic additives such as oxalic acid, succinic acid and L-aspartic acid (all three) having COOH group(s) with aspartic acid having an additional NH2 group, are investigated for gas hydrate promotion/inhibition behavior. These compounds are polar in nature and thus have significant solubility in liquid water; the presence of weak acidic and water loving (carboxylic/amine groups) moieties makes these organic acids an excellent candidate for further study. This study would pave ways to identify a novel(read better) promoter/inhibitor for gas hydrate formation. Suitable thermodynamic conditions were generated in a stirred tank reactor coupled with cooling system; comparison of gas hydrate formation kinetics with and without additives were carried out to identify the effect of these acids on the formation and growth of hydrates. The possible mechanisms by which these additives inhibit or promote the hydrate growth are also discussed.

Methane hydrate dissociation in the presence of novel benign additives

The apparent drawbacks of the classical approaches towards dissociation of natural gas hydrates have resulted in a paradigm shift into the development of new hybrid hydrate dissociation practices combining the various basic hydrate dissociation techniques. Another approach that can be followed to maximize the efficiency of gas production from natural gas hydrate reserves is the identification of benign additives which when used even in sparingly small concentrations may enhance the kinetics of hydrate dissociation. In the present work, a class of such additives, never reported before, have been unveiled and christened as Low Dosage Hydrate Dissociation Promoters (LHDPs). The additives were first short listed from a wide potential pool using a lab scale (~250 ml) stirred tank reactor setup and then further studied using a bench scale (~2.35 l) reactor setup where they were injected in the form of a water-additive stream to dissociate hydrates. The dissociation approach followed in the case of the bench scale reactor experiments was a combination of the thermal stimulation and depressurization processes along with the element of injection of additives. For both sets of experiments (lab and bench scale), the newly identified LHDPs were found to enhance the kinetics of methane hydrate dissociation as compared to pure water. It was observed that concentration of additive and its flow rate also affect the kinetics of methane hydrate dissociation. An energy and efficiency analysis for the hydrate dissociation method in the case of bench scale rector revealed that additive presence enhanced the energy ratio and thermal efficiency four fold as compared to pure water.

Study on the decomposition conditions of gas hydrate in quartz sand-brine mixture systems

There are huge reserves of natural gas hydrates, a type of low-carbon energy resource, and it is considered important to study the stability conditions of hydrates in situ, to facilitate reserve evaluation and exploitation. The decomposition conditions of methane hydrate were determined in a quartz sand-brine mixing system, using an isothermal, stepwise, depressurising method. Influencing factors, such as sand particle size and pore water salt concentration, and the combined effect of these factors on the hydrate phase equilibrium, were investigated. The results showed that the decomposition pressure was distributed over a small range, and at specific temperatures. This may be partly related to the uneven distribution of pore size, but was shown to be mainly owing to the change of salt concentration during hydrate dissociation, as verified by differential scanning calorimetry. In addition, the hydrate dissociation pressure increased slightly with decreased particle size, and the maximum relative deviation of the dissociation pressure was 1.68%, when the sand particle size was within 100 mesh, which was mathematically negligible. For predicting the decomposition condition of hydrate in the quartz sand-brine mixing system, commercially-available CSMgem and PVTsim software showed high accuracy across a large temperature interval. An in-house, Chen-Guo hydrate model was valid when the temperature was below 277 K, while the Multiflash programme exhibited too large an error to be applied to this system.

Investigation method of borehole collapse with the multi-field coupled model during drilling in clayey silt hydrate reservoirs

The global reserves of natural gas hydrates are extremely abundant, which is attracting more and more scientists’ attention. However, hydrate reservoirs are usually clayey silt hydrate reservoirs with low strength, borehole collapse is a key issue during the drilling operation in these clayey silt hydrate reservoirs in the South China Sea. Therefore, investigation method exploration of borehole collapse simulation for wellbores drilled in hydrate-bearing sediments is of great importance for safely and efficiently developing hydrate in deep water. The finite element model coupled seepage, deformation and heat transfer is developed, and borehole collapse investigation during the overbalanced drilling operation in hydrate-bearing sediment is carried out. The results show that changes in temperature and/or pore pressure do not necessarily lead to the hydrate dissociation. For the investigation case, the temperature front reaches to the position of 35.72 cm from borehole within the near-wellbore area when the drilling operation lasted for 3 hours, but hydrate only dissociates for 17.94cm from the borehole, which is smaller than the temperature disturbance distance. Moreover, the applicability of the investigation method developed herein is verified by comparing the equivalent plastic strains obtained by the coupled model developed in this paper and the simplified model (which neglects the seepage and the heat transfer) respectively. All these results demonstrate that both the investigation method and the finite element model can be used for borehole stability simulation in hydrate-bearing sediments.

Effect of silica sand size and saturation on methane hydrate formation in the presence of SDS

Abundant reserves of natural gas hydrates are hosted in the pores of sediment layers, and the hydrate-based technology could be widely used in industry. In this work, the formation kinetics of methane hydrate in a complex system containing silica sand and 300-ppm sodium dodecyl sulfate (SDS) solution were investigated at 275.15 K and 7 MPa. The hydrate was formed in different-saturated silica sand with particle sizes of 100, 150, 200, 300, and 400 mesh. The results indicated that in both the 50%- and 100%-saturated sand, a larger particle size exhibited a better methane storage capacity. In the complex system, the presence of SDS molecules significantly enhanced the hydrate formation process and weakened the effect of particle size on the hydrate formation rate. The difference in hydrate gas uptake formed in the differently saturated silica sand indicted that with an increase in saturation, the smaller-sized silica sands caused a more marked inhibitory effect. Finally, the different hydrate distributions in the 50%- and 100%-saturated silica sand revealed that a hydrate film formed quickly and preferentially on the surface of the silica sand, which was attributed to the adsorption of the SDS active groups and the presence of the silica sand surface. With the thickening of the hydrate film, the resulting volume expansion and stronger capillary force led to the migration of the liquid phase, which resulted in the hydrate distributions observed in the differently saturated silica sands.

Dissociation characteristics of water-saturated methane hydrate induced by huff and puff method

The world has huge reserves of gas hydrates which are considered to be a potential energy resource. Therefore, developing methods for commercial gas production from hydrate reservoirs are attracting extensive attention. In order to mimic the geological condition of the practical oceanic hydrate reservoir, water-saturated hydrate sample with low gas saturation (8.27%) was obtained by the formation process of multi-step water injection. The huff and puff (H&P) method (above or below the equilibrium pressure for hydrate dissociation) was applied for hydrate dissociation. Results show that the system pressure rises with the increase of the H&P cycle for the H&P method above the equilibrium pressure. Furthermore, the dissociated hydrate in the injection period can be reformed in the soaking and production periods, and hydrate saturation increases mildly after each cycle of H&P. Hence, the H&P method above the equilibrium pressure is unpractical for hydrate dissociation with low gas saturation. However, the hydrate in the reservoir can be completely dissociated by the H&P method below the equilibrium pressure. Therefore, in the water-saturated hydrate reservoir, the regular H&P method is not suitable. The regular H&P should combine with depressurization method for gas recovery from the water-saturated hydrate reservoir.

Heat and mass transfer analysis of depressurization-induced hydrate decomposition with different temperatures of over- and underburden

Natural Gas Hydrate (NGH) reserves are large and regarded as an important alternative future energy source. Safely and efficiently exploiting natural gas hydrates has recently become a hot issue around the world. The decomposition of natural gas hydrate requires a great deal of absorbed heat. The decomposition process is a complicated heat and mass transfer process with phase changes, such that heat and mass transfer will have a great impact on the decomposition results. Focusing on the heat transfer effect, a two dimensional mathematical model of natural gas hydrate decomposition was established. Using a numerical simulation method, the thermal conductivities of different porous mediums were selected and the bottom hole pressure (BHP) was changed under different overburden and underburden temperatures to simulate the depressurization exploitation of natural gas hydrates. The reservoir temperature distribution, hydrate decomposition front, gas production rate, and cumulative gas production under different cases were obtained. The results show that the incoming heat directly influenced the reservoir temperature distribution, hydrate decomposition rate, and gas production and the temperature at any point on the decomposition front is constant under certain BHP. When there was no external heat introduced into the hydrate-bearing layers, the impact of thermal conductivity on decomposition was greater, but decreased with increasing temperature of overburden and underburden. When no external heat was introduced into the hydrate-bearing layers, the BHP became the main controlling factor of the cumulative gas production, and the effect of the BHP on the cumulative gas production was gradually weakened with increasing temperatures of the overburden and underburden.

Gas Hydrate—Properties, Formation and Benefits

There are numerous gas hydrate reserves all over the world, especially in permafrost regions and ocean environments. The abundance of gas hydrate reserves is estimated to be more than twice of the combined carbon of coal, conventional gas and petroleum reserves. These hydrate deposits hold significant amount of energy which can make hydrate a sustainable energy resource. The comprehensive research on the properties and formation of methane hydrates is paramount to ensure efficient and effective exploration and development of hydrate reserves. Natural gas is mostly distributed for different purposes through pipelines or pressure vessels such as dry gas, compressed gas or liquefied gas, which means transporting natural gas creates serious safety concerns because methane is highly flammable and almost impossible to detect any leak without using odorant. Alternatively, natural gas can be stored and transported as gas hydrate turns solid or slurry. Gas hydrate can be stored at equilibrium conditions with either saturation temperature or pressure. The equilibrium conditions are influenced by the cost and weight of storage vessel. Hydrate can be transported either as slurry or solid depending on the location of target or destination. The slurry form is usually a better option for distance of approximately 2500 mile or less while the solid form can be used for distances of roughly 3500 miles or more. The paper examines the properties, formation and benefits of gas hydrate. The suitability of gas hydrate as a sustainable energy resource and the possibility of using gas hydrate for the transportation and storage of natural gas (methane) are also stated. Natural gas transportation and storage as gas hydrate will create effectively and efficiently alternative bulk gas transportation and storage for future use of the gas.

Hole-bottom freezing method for gas hydrate sampling

The analysis of core samples is an essential component in the evaluation of natural gas hydrate (NGH) reserves. To prevent NGH volatilization in the sampling process, the commonly employed pressure-temperature preservation technique is used to maintain the temperature-pressure condition of the NGH core at its in situ value. However, the structure of a typical pressure-temperature preservation sampler is notably complicated, the diameter of the core is small, and the insulation effect is poor. To solve these problems, we propose a hole-bottom freezing sampling technique that uses liquid nitrogen as a cold source to decrease the temperature of the NGH core, which reduces its critical breakdown pressure and promotes the self-preservation of NGHs. We also propose two different types of hole-bottom freezing samplers, which are denoted as the cold-source built-in freezing sampler and the cold-source external freezing sampler. Both experimental tests and numerical simulation of the heat-transfer process during core freezing were conducted to evaluate the freezing efficiency of the new method. We calculated and compared the liquid-nitrogen consumption of the two different types of samplers in the process of NGH sampling. The results demonstrate that greater efficiency is obtained using the proposed cold-source external freezing sampler.

Assessment of the response of subaqueous methane hydrate deposits to possible climate change in the twenty-first century

Large reserves of methane are trapped in oceanic hydrate deposits. Increase in temperature of the oceans makes a contribution to the dissociation of oceanic hydrate accumulations and release of poten� tially large amounts of methane into the atmosphere. Such releases into the atmosphere lead to an increase in the greenhouse effect and, accordingly, serious climate changes and to accelerate the gas hydrate dissociation. In this work we evaluated the sta� bility of the existing reserves of subaqueous (underwa� ter) gas hydrates and possible methane release with the dissociation of methane hydrates in the twentyfirst century (1). Methane hydrates are compounds in which meth� ane molecules are in cells formed by water molecules. They are widely distributed in the permafrost zones and the oceanic bottom sediments along the continental slopes, where they are stable at the current PTvalues. Methane hydrates are a potentially large source of energy in comparison with other known sources of hydrocarbons. The total carbon in hydrates is esti� mated as 10 4 Gton C (2), which is a significant amount in comparison with the carbon content (3.8 ×10 4 Gton C) dissolved in the oceanic water and in soil and plants (2 × 10 3 Gton C) and the atmosphere (7.3 ×10 2 Gton C) (3). The total fossil fuel reserves, including coal, are about 5 ×10 3 Gton C (4); i.e., they are consistent with gas hydrate reserves. Methane is the third (after water vapor and carbon dioxide) greenhouse gas, which has a significant effect on the radiation balance of Earth's climate system and can be released into the atmosphere as a result of min� ing and use of hydrates as an energy source. Sudden releases of methane into the atmosphere may occur due to massive underwater shifts of the Earth's crust and an increase in temperature in the oceanic bottom sediments. According to the model estimates, in case of an increase in the oceanic water temperature by a few degrees, methane hydrate reserves should be much smaller (5). Releases of methane in decomposition of methane hydrates could have been a cause of abrupt climate change in the past (6, 7). The Paleocene- Eocene temperature maximum is a wellknown exam� ple of a period of abrupt climate change that was likely associated with massive release of methane from hydrates 55 Ma ago. In some areas (including the Car� ibbean Sea, North Atlantic, the Weddell Sea, and tropical Pacific Ocean), a shift of 2.5- δ 13 С in biogenic carbonate and organic matter was noted. This may be associated with the release of 1500-2000 Gton of methane over several thousand years (6). Such a large release of methane could influence cli�

Review on the gas hydrate development and production as a new energy resource

Gas hydrates consist of guest gas molecules inside hydrogen-bonded water lattices. Natural gas hydrates are found in offshore and permafrost regions. The large amounts of gas hydrate reserves suggest the potential of gas hydrates as an energy resource if economically viable production methods were developed. The proper understandings of hydrate formation/dissociation are important for the drilling and oil production applications. The investigations of physical and geotechnical properties provide the in-depth understandings of the in-situ hydrate formation mechanism and the associated production technologies. The purpose of this review paper is to provide a starting kit for civil engineers who have recently started the research related to the hydrate development and production and want to have insights on the general trends of the hydrate research and the relevant knowledge needed for their research. Gas hydrate explorations include the geophysical explorations, such as the seismic survey, the borehole logging and the geological and geochemical explorations. Gas hydrate productions require the dissociation of gas hydrates, and the production technologies are categorized based on the dissociation techniques involved: depressurization method, thermal stimulation method, and inhibitor injection method. Establishing safe and efficient gas production technology requires the extensive information on the geotechnical characteristics of hydrate reservoirs. Flow assurances, the integrity of sediment formation and the well bore stability are crucial for the safe and efficient productions of gases from gas hydrates in sediments. The strength and deformation characteristics, the fluid migration characteristics, and the thermal conduction characteristics are key factors for controlling the above.

A seismic study to investigate the prospect of gas hydrate in Mahanadi deep water basin, northeastern continental margin of India

The presence of gas hydrates, one of the new alternative energy resources for the future, along the Indian continental margins has been inferred mainly from bottom simulating reflectors (BSR) and the gas stability zone thickness mapping. Gas hydrate reserves in Krishna Godawari Basin have been established with the help of gas-hydrate related proxies inferred from multidisciplinary investigations. In the present study, an analysis of 3D seismic data of nearly 3,420 km2 area of Mahanadi deep water basin was performed in search of seismic proxies related with the existence of natural gas hydrate in the region. Analysis depicts the presence of BSR-like features over a large areal extent of nearly 250 km2 in the central western part of the basin, which exhibit all characteristics of a classical BSR associated with gas hydrate accumulation in a region. The observed BSR is present in a specific area restricted to a structural low at the Neogene level. The coherency inversion of pre-stack time migration (PSTM) gathers shows definite inversion of interval velocity across the BSR interface which indicates hydrate bearing sediments overlying the free gas bearing sediments. The amplitude versus offset analysis of PSTM gathers shows increase of amplitude with offset, a common trend as observed in BSR associated with gas hydrate accumulation. Results suggest the possibility of gas hydrate accumulation in the central part of the basin specifically in the area of structural low at the Neogene level. These results would serve as preliminary information for selecting prospective gas hydrate accumulation areas for further integrated or individual study from geophysical, geological, geochemical and microbiological perspectives for confirmation of gas hydrate reserves in the area. Further, on the basis of these results it is envisaged that biogenic gas might have been generated in the region which under suitable temperature and pressure conditions might have been transformed into the gas hydrates, and therefore, an integrated study comprising geophysical, geological, geochemical and microbiological data is suggested to establish the gas hydrate reserves in Mahanadi deep water basin.

Direct seismic indicators of gas hydrates in the Walker Ridge and Green Canyon areas, deepwater Gulf of Mexico

During the past two decades, marine research has focused on gas hydrates because of their potential importance as a future energy source, as a geologic hazard in deepwater hydrocarbon exploration, and because they may impact climate change (McConnell and Kendall, 2003; Smith et al., 2005). Worldwide assessments indicate that gas hydrate reserves may surpass the total hydrocarbon reserves from all other known resources of fossil fuels. Consequently, gas hydrates are considered to be a potential energy source for the 21st century.