Methane Hydrate Deposits Research Articles

Machine-learning application to assess occurrence and saturations of methane hydrate in marine deposits offshore India

Artificial neural networks (ANN) were used to assess methane hydrate occurrence and saturation in marine sediments offshore India. The ANN analysis classifies the gas hydrate occurrence into three types: methane hydrate in pore space, methane hydrate in fractures, or no methane hydrate. Further, predicted saturation characterizes the volume of gas hydrate with respect to the available void volume. Log data collected at six wells, which were drilled during the India National Gas Hydrate Program Expedition 02 (NGHP-02), provided a combination of well-log measurements that were used as input for machine-learning (ML) models. Well-log measurements included density, porosity, electrical resistivity, natural gamma radiation, and acoustic wave velocity. Combinations of well logs used in the ML models provide good overall balanced accuracy (0.79 to 0.86) for the prediction of the gas hydrate occurrence and good accuracy (0.68 to 0.92) for methane hydrate saturation prediction in the marine accumulations against reference data. The accuracy scores indicate that the ML models can successfully predict reservoir characteristics for marine methane hydrate deposits. The results indicate that the ML models can either augment physics-driven methods for assessing the occurrence and saturation of methane hydrate deposits or serve as an independent predictive tool for those characteristics.

Effect of Lithological Parameters on Combustion Characteristics of Methane Hydrate Sediments

In this paper, four lithological parameters, that is, thermal conductivity, particle size, porosity, and saturation, are investigated by combining experimental observations with numerical simulations to study the influence laws and mechanisms of action on the combustion process of methane hydrate sediments. The variations in combustion characteristics parameters such as flame height, effective combustion ratio, and dimensionless discharge water mass with the lithological parameters are studied. In addition, the combustion mechanism of lithologic parameters on methane hydrate deposits is revealed. Combining the experimental results and simulation calculations to optimize the combustion of methane hydrate sediments, it is recommended to use methane hydrate sediment samples with high saturation and low thermal conductivity, while the oxidant concentration and porosity of methane hydrate sediment samples should be increased.

Depressurization assisted CO2-CH4 replacement in hydrate Structure: Molecular mechanism and kinetic modeling

Methane hydrates as a source of energy and a medium for long-term storage of anthropogenic CO2 gained many attentions in the recent years. Methane hydrate deposits can secure the energy demand in the world for decades. CO2-CH4 replacement technique is a state of art for exploitation of methane hydrate deposits and simultaneously under-ground CO2 storage. This technique covers lots of shortages existing in conventional techniques for production from methane hydrate reservoirs. Due to the complexity of this process, there is not a clear insight from the mechanism of replacement. Additionally, slow rate of replacement makes this method technically and economically inefficient. Combining CO2-CH4 replacement and depressurization techniques is a novel rout to enhance the rate of methane recovery. Here we search for the molecular mechanism of CO2-CH4 replacement in depressurized CH4 hydrate in the presence of excess water by experiments conducted in a constant stirred hydrate crystallizer. A representative kinetic model is developed based on the confirmed molecular mechanism. According to the proposed mechanism, the replacement reaction includes two steps; partial breakage of methane hydrate cages, and exchange between CO2 and CH4 in damaged cages and reestablishing hydrate structure. In addition to the replacement reaction, a new mixed CO2 + CH4 hydrate will form from the existing free water, and some portions of the damaged methane hydrates decompose completely. Proportionality of the replacement rate with methane fugacity difference reveals that partial breakage of hydrate cages is the rate limiting step of the replacement reaction. Replacement kinetic parameters extracted from the proposed kinetic model and experimental data are correlated over a wide range of operational conditions.

Resident autonomous underwater vehicles for persistent mobile ocean observing

Whether near shore or in the open ocean, stationary ocean observing systems lack the ability to respond spatially to transient and difficult-to-predict phenomena, such as mid-ocean ridge eruptions, instabilities in methane hydrate deposits, turbidite flows, sea–ice interactions, mass wasting events, or changes in coastal currents. Detecting and characterizing these types of events and the processes driving them requires mobile systems available at the time of the event onset. Ideally, mobile autonomous underwater vehicles (AUVs) would permanently be stationed in or near areas where events of interest are likely to occur. Traditionally, due to their dependence on batteries, AUV mission durations are often measured in hours and require costly on-water support vessels and human intervention, making it impractical to sustain a mobile observing presence. However, advances in cabled power/comms and renewable marine energy technologies present significant opportunities for developing persistent mobile subsea systems able to recharge their batteries from fixed underwater infrastructure. In addition to power, these “resident” AUVs will require navigation and data transmission support. Acoustic systems will play key roles as sensing systems, navigation, vehicle homing, data transfer, and advanced robotic operations. This talk will present an overview of the systems and concepts relevant to subsea mobile ocean observing systems along with example applications.

Methane Hydrate in Marine Sands: Its Reservoir Properties, Gas Production Behaviors, and Enhanced Recovery Methods

Since the discovery of methane hydrate in marine sands in 1999, our understanding of methane-hydrate-bearing sediments has progressed rapidly. Comprehensive studies of methane hydrate deposits in the Nankai Trough have made a great contribution to this research. Reservoir evaluation combining geophysical logging with pressure core analysis has become the standard protocol for exploring methane-hydrate-bearing sands, revealing that the effective permeability of methane-hydrate-bearing sands lies in the range of 1-100 md, even if the hydrate saturation reaches high value of 50-80 % in pores. Numerical and experimental studies of gas production have demonstrated that fluid flow and heat transfer are key rate-determining factors for field-scale depressurization-induced gas production. In that sense, the high permeability of methane-hydrate-bearing sands indicates the applicability of depressurization as a primary gas production method; however, a lack of heat limits hydrate dissociation and thus the recovery factor cannot exceed approximately 40 %. Thus, enhanced recovery methods are necessary to increase viability of commercialization. Experimental and numerical studies have shown that hydraulic fracturing enhances production rate, and that cyclic depressurization assisted by geothermal and deep depressurization using the latent heat of ice formation are possible means by which the enhancement of the recovery factor can be achieved while maintaining energy efficient production.

Genome sequencing and analysis of a psychrotrophic methanogen Methanosarcina sp. nov. MSH10X1 cultured from methane hydrate deposits of Krishna Godavari Basin of India.

Methanosarcina sp. strain MSH10X1, a psychrotrophic methanogen, was isolated from sub-seafloor methane hydrate deposits of Krishna Godavari Basin on India's east coast. The strain could grow from 5 to 40°C following all three i.e. methylotrophic, acetoclastic, and hydrogenotrophic modes of methanogenesis utilizing different substrates like methanol, trimethylamine, H2/CO2 (80/20), acetate, valerate, isobutyrate, isopropanol, and isobutanol. The genome sequencing and analysis of this strain revealed a circular chromosome of 3,557,383bp length having 42.47mol%G+C content, which consisted of 3110 coding genes, 58 tRNA genes, and 3 rRNA operons. The KEGG analysis highlighted the presence of genes responsible for all three modes of methanogenesis. The presence of genes like mtaB, mtaC, and mttB in the genome provided evidence for possible adaptation of strain MSH10X1 in the deep sea's low-temperature conditions.

Optimization of Gas Production from Marine Methane Hydrate Deposit Induced by Horizontal Well

Methane hydrate (MH) has attracted increasing interest as one potential alternative clean energy. However, creating efficient MH field tests is a great challenge faced by the industry. It requires ...

Numerical modeling of gas production from methane hydrate deposits using low-frequency electrical heating assisted depressurization method

With the increasing global demand for clean energy, methane hydrate has been regarded as a potential alternative energy source in future due to its huge resources and high energy density. In this study, a mathematical model is established to evaluate the production performance of low-frequency electrical heating assisted depressurization (LF-EHAD) method for hydrate deposits recovery. Within the framework of this model, the integral finite difference method and Newton-Raphson iteration are employed for solution, which is then validated by the experiment data. Using this model, the energy recovery behaviors with LF-EHAD from Shenhu hydrate deposits are investigated and then compared with those performed by hot water flooding and depressurization. Simulation results show that hydrate dissociation and gas production are significantly enhanced as a result of sufficient heat supplied by the electrical heating, validating the potential of the LF-EHAD for hydrate deposits recovery. After 2000 days of production, the cumulative gas production of LF-EHAD and hot water injection are 2.37 times and 1.47 times of that conducted by the depressurization method. Moreover, the heat consumption used to increase the formation temperature in the hydrate dissociation region under LF-EHAD is much less than that of hot water flooding, which results in a higher energy efficiency ratio (EER) of 9.65 for LF-EHAD, while the EER of hot water flooding is 4.42. Overall, LF-EHAD shows better performance than hot water flooding with the same amount of heat input because of higher gas production and energy utilization efficiency, but lower water production.

An experimental description of the double positive effect of CO2 injection in methane hydrate deposits in terms of climate change mitigation

In this paper, the possibility of injecting CO2 into a hydrate reservoir, with the only aim of preventing methane release was investigated. Pure methane hydrates were formed and then partially dissociated, due to a provoked temperature increase of 2 °C. The same procedure was applied to a system composed by a core of CH4 hydrates and an external shell made with CO2 hydrates. In tests with only methane hydrate, that temperature increase caused partial hydrate dissociation, with a consequent increase in pressure about 7.81–8.42 bar. In presence of CO2 hydrate, the same temperature increase did not cause any dissociation, even if the new established condition were not suitable for CH4 hydrates stability. Results proved that CO2 is capable to form a strong hydrate shell around the methane core, which hinders its dissociation. Two positive contributions were reached: CO2 permanent storage and the prevention of CH4 release in the atmosphere.

Experimental laboratory complex for studying the physical properties of artificially formed gas-hydrate-containing sediments

Physical properties of gas hydrate-containing sediments (HCS) are extremely important information for the development of methods for their search and exploration. The presence of gas hydrates in marine bottom sediments significantly changes their physical properties, so they can be detected by marine remote geophysical observations. The physical properties of HCS are very important for detecting the presence of these compounds, estimating the amount of captured gas hydrates by sediments, as well as developing methods for using this resource. Currently, the study of physical properties concerned mainly artificial gas hydrates in the process of formation and decomposition under various thermodynamic conditions in their pure form. Therefore, very little is known about the physical properties of HCS, which makes their detection by remote geophysical surveys too difficult. Development and creation of experimental laboratory modular complex for formation of artificial methane gas hydrates in various lithological-granulometric matrices (sandstones, argillites, siltstones, etc.) and measurement of their physical properties in thermodynamic conditions of bottom sediments of the Black Sea, will increase efficiency technology of methane hydrate deposits development. Under experimental conditions, along with the thermal conductivity and velocities of longitudinal and transverse waves of artificial HCS, the parameters of elastic deformation, strength, and decay characteristics will be measured, which will allow performing theoretical analysis to build models based on different hypotheses of their genesis. At the S.I. Subbotin Institute of Geophysics of the National Academy of Sciences of Ukraine created a model of the installation for the formation and study of the physical properties of HCS. The development is based on the modern technological level of research in the field of thermobaric petro- physical experimental modeling of geological environments, as well as on the use of modern software and hardware laboratory research to obtain physical properties of bottom sediments of various lithological and particle size distribution.

Investigation of the dissipative structures following microseismic diffusion during hydraulic fracturing of methane-hydrate-bearing sand

Hydraulic fracturing is a prospective technology for methane hydrate deposit exploitation. The evolution of hydraulically stimulated fractures around the point of liquid injection is simulated. For this purpose, the FLAC3D computer model is used because of its explicit calculation cycle that imitates real physics, prevents numerical instability, and reproduces a realistic path during simulation of the nonlinear rock massif behavior. The results of the simulation provide for new findings, namely, the spatial asymmetry and synchronism violation, spatial deviation, discontinuity, and recurrence during microseismic diffusion, which follow the process of hydraulic fracturing. In addition, dissipative structures were developed due to entropy production, since gas hydrate strata are an open thermodynamic system, which transforms and dissipates the energy of the injected liquid. The process of dissipative structure evolution should be controlled to enhance the gas yield from the hydrates.

Production Behaviors of Water-Saturated Methane Hydrate Deposits during the Depressurization with/without Thermal Water Compensation Process

Marine methane hydrate is an important source of energy for the future, attracting great attention of global researchers and many governments. The water-saturated hydrate deposit is more similar to...

Numerical evaluation of free gas accumulation behavior in a reservoir during methane hydrate production using a multiple-well system

This study aimed to investigate the free gas accumulation behavior in a reservoir using a multiple-well system for methane hydrate production achieved by depressurization. Twenty-year simulations of gas production from a large-scale 3D methane hydrate reservoir model with different reservoir permeabilities were conducted, and the effects of different reservoir and operating conditions on the free gas accumulation behavior were fully examined. The simulation results indicated that the free gas accumulation behavior was affected by the reservoir permeability, and methane gas was inclined to accumulate within a certain permeability range, which was defined as the “free gas accumulation zone” for the first time. For an actual methane hydrate reservoir with a porosity of 0.31–0.51 and an initial hydrate saturation of 0.34–0.54, the free gas accumulation zone was estimated to be 37–145 mD at most. On the other hand, a low wellbore pressure could contribute to enhancing gas recovery by narrowing the free gas accumulation zone. In addition, the free gas accumulation zone was dramatically enlarged with the increase in well spacing, so a proper well spacing should be carefully designed to avoid the free gas accumulation zone. The prediction method proposed in this study could be applied to future commercial gas production from actual methane hydrate deposits achieved by depressurization using multiple-well systems.

Experimental study on methane hydrate formation in quartz sand under tri-axial condition

Methane hydrate (MH) has been considered as one of the cleanest energy resources. Its huge resource reserve and high energy density have attracted widespread attention in the scientific field. The dynamic behavior of MH formation and the resulting hydrate saturation are greatly influenced by the conditions of the formation process, such as water-gas ratio (WGR), pressure (P), temperature (T), and the mass fraction of NaCl (XNaCl). To gain a better understanding of the kinetic behavior of the in-situ MH deposits, a novel tri-axial horizon fixed bed reactor was set up to synthesize MH samples under typical marine conditions. A series of MH formation experiments were conducted under similar initial stress conditions (initial tri-axial stress of 16.50 MPa to simulate the overburden stress of marine MH) while perturbing the other key factors (WGR, P, T, and XNaCl) to investigate their effects. The results show that MH saturation attained at the end of formation from an initial water-gas mixing condition was negatively affected by initial WGR, T, and the existence of NaCl. MH formation in the fixed bed reactor increases initial XNaCl = 3.0 wt% to a maximum of XNaCl = 5.29 wt% and shifts the MH equilibrium curve to a more stringent condition for MH formation. Higher pressure promotes CH4 conversion to MH and increases MH saturation from the start of gas injection to the time when the pressure of the reactor was stable (ΔP < 20 kPa/h). Larger initial WGRs (above MH hydration number = 5.75) and higher pressures result in a reduction of the induction time. Increasing temperature and the presence of NaCl increase the induction time.

Enhanced CH4-CO2 Hydrate Swapping in the Presence of Low Dosage Methanol

CO2-rich gas injection into natural gas hydrate reservoirs is proposed as a carbon-neutral, novel technique to store CO2 while simultaneously producing CH4 gas from methane hydrate deposits without disturbing geological settings. This method is limited by the mass transport barrier created by hydrate film formation at the liquid–gas interface. The very low gas diffusivity through hydrate film formed at this interface causes low CO2 availability at the gas–hydrate interface, thus lowering the recovery and replacement efficiency during CH4-CO2 exchange. In a first-of-its-kind study, we have demonstrate the successful application of low dosage methanol to enhance gas storage and recovery and compare it with water and other surface-active kinetic promoters including SDS and L-methionine. Our study shows 40–80% CH4 recovery, 83–93% CO2 storage and 3–10% CH4-CO2 replacement efficiency in the presence of 5 wt% methanol, and further improvement in the swapping process due to a change in temperature from 1–4 °C is observed. We also discuss the influence of initial water saturation (30–66%), hydrate morphology (grain-coating and pore-filling) and hydrate surface area on the CH4-CO2 hydrate swapping. Very distinctive behavior in methane recovery caused by initial water saturation (above and below Swi = 0.35) and hydrate morphology is also discussed. Improved CO2 storage and methane recovery in the presence of methanol is attributed to its dual role as anti-agglomerate and thermodynamic driving force enhancer between CH4-CO2 hydrate phase boundaries when methanol is used at a low concentration (5 wt%). The findings of this study can be useful in exploring the usage of low dosage, bio-friendly, anti-agglomerate and hydrate inhibition compounds in improving CH4 recovery and storing CO2 in hydrate reservoirs without disturbing geological formation. To the best of the authors’ knowledge, this is the first experimental study to explore the novel application of an anti-agglomerate and hydrate inhibitor in low dosage to address the CO2 hydrate mass transfer barrier created at the gas–liquid interface to enhance CH4-CO2 hydrate exchange. Our study also highlights the importance of prior information about methane hydrate reservoirs, such as residual water saturation, degree of hydrate saturation and hydrate morphology, before applying the CH4-CO2 hydrate swapping technique.

Experimental and modeling study of the kinetics of methane hydrate formation and dissociation

In this work, several experiments were conducted at isobaric and isothermal condition in a CSTR reactor to study the kinetics of methane hydrate formation and dissociation. Experiments were performed at five temperatures and three pressure levels (corresponding to equilibrium pressure). Methane hydrate formation and dissociation rates were modeled using mass transfer limited kinetic models and mass transfer coefficients for both formation and dissociation were calculated. Comparison of results, shows that mass transfer coefficients for methane hydrate dissociation are one order greater than formation conditions. Mass transfer coefficients were correlated by polynomials as relations of pressure and temperature. The results and the method can be applied for prediction of methane production from naturally occurring methane hydrate deposits.

Radial spreading of turbulent bubble plumes.

Weak bubble plumes carry liquid from the environment upwards and release it at multiple intermediate levels in the form of radial intrusive currents. In this study, laboratory experiments are performed to explore the spreading of turbulent axisymmetric bubble plumes in a liquid with linear density stratification. The thickness, volumetric flowrate and spreading rates of multiple radial intrusions of plume fluid were measured by tracking the movement of dye injected at the source of bubbles. The experimental results are compared with scaling predictions. Our findings suggest that the presence of multiple intrusions reduces their spreading rate, compared to that of a single intrusion. This work is of relevance to the spreading of methane plumes issuing from the seabed in the Arctic Ocean, above methane-hydrate deposits. The slower, multiple spreading favours the presence of methane-rich seawater close to the plume, which may reduce the dissolution of methane in the bubbles, and thus promote the direct transport of methane to the atmosphere. This article is part of the theme issue 'Stokes at 200 (part 2)'.

Experimental study on the permeability of methane hydrate-bearing sediments during triaxial loading

The permeability of methane hydrate (MH)-bearing sediments is closely related to the exploitation efficiency of MH deposits. During the exploitation of MHs, the stress state of hydrate-bearing reservoirs is complex, and stratum deformation may occur simultaneously. Both the change in the stress state and stratum deformation may influence the permeability of hydrate-bearing sediments. In this paper, a series of permeability measurement tests was conducted to study the influence of the effective confining pressure and triaxial compression process on the permeability of MH-bearing samples. The test results indicated that the permeability of hydrate-bearing samples was influenced by the effective confining pressure. With increasing effective confining pressure, the permeability of the pure sand sample gradually decreased. For the hydrate-bearing samples, the permeability was also influenced by the effective confining pressure. When the effective confining pressure reached a specific value, a sharp drop in the permeability of the hydrate-bearing samples occurred. The change in permeability might be caused by the increase in fine hydrate particles in the pore space. Based on the test results, the permeability of the hydrate-bearing samples was influenced by the triaxial compression process. During the shearing process, the permeability greatly increased when the axial strain reached a specific value. This phenomenon might be caused by the formation of a shear band. During the production of hydrates, controlling the change in stress applied to the hydrate particles could possibly promote production. Furthermore, the appearance of shear bands or fissures might also increase production by certain methods, such as the hydraulic fracturing process.

Geochemical insights into contribution of petroleum hydrocarbons to the formation of hydrates in the Taixinan Basin, the South China Sea

Methane hydrate in the South China Sea (SCS) has extensively been considered to be biogenic on the basis of its δ13C and δD values. Although previous efforts have greatly been made, the contribution of thermogenic oil/gas has still been underestimated. In this study, biomarkers and porewater geochemical parameters in hydrate-free and hydrate-bearing sediments in the Taixinan Basin, the SCS have been measured for evaluating the contribution of petroleum hydrocarbons to the formation of hydrate deposits via a comparative study of their source inputs of organic matters, environmental conditions, and microbial activities. The results reveal the occurrence of C14–C16 branched saturated fatty acids (bSFAs) with relatively high concentrations from sulfate-reducing bacteria (SRBs) in hydrate-bearing sediments in comparison with hydrate-free sediments, which is in accord with the positive δ13C values of dissolved inorganic carbon (DIC), increasing methane concentrations, decreasing alkalinity, and concentration fluctuation of ions (Cl−, Br−, SO42−, Ca2+, and Mg2+). These data indicate the relatively active microbial activities in hydrate-bearing sediments and coincident variations of environmental conditions. Carbon isotope compositions of bSFAs (−34.0‰ to −21.2‰), n-alkanes (−34.5‰ to −29.3‰), and methane (−70.7‰ to −69.9‰) jointly demonstrate that SRBs might thrive on a different type of organic carbon rather than methane. Combining with numerous gas/oil reservoirs and hydrocarbon migration channels in the SCS, the occurrence of unresolved complex mixtures (UCMs), odd-even predominance (OEP) values (about 1.0), and biomarker patterns suggest that petroleum hydrocarbons from deep oil/gas reservoirs are the most probable carbon source. Our new results provide significant evidence that the deep oil/gas reservoirs may make a contribution to the formation of methane hydrate deposits in the SCS.

3D investigation of the effects of multiple-well systems on methane hydrate production in a low-permeability reservoir

The utilization of multiple-well systems was proposed as a novel approach for the future commercial gas production from offshore methane hydrate deposits. In order to investigate their effects on methane hydrate production in a low-permeability reservoir, a 3D reservoir model combined with multiple-well systems was established in this study, and long-term numerical simulations of gas production from methane hydrate reservoirs by depressurization were conducted to reveal the complex phenomena of pressure propagation, heat transfer, and gas-liquid two-phase flow in different production systems through 3D visualization. Furthermore, the hot water injection method was also applied in the multiple-well system to examine its effect on gas recovery enhancement. The numerical analyses indicated that the dual-well system had the best performance in gas recovery in a low-permeability reservoir by depressurization, while with the increase in well number, the gas production potential decreased contrarily. In addition, “blind area effect” was found for the first time, which was likely to occur in a low-permeability reservoir when using multiple-well systems (well number > 2) by depressurization. This phenomenon was essentially caused by secondary hydrate formation in the reservoir, which would result in the free gas accumulation in the center region of the vertical wells and thus the decrease in gas production. The hot water injection method could eliminate the blind area effect by preventing secondary hydrate formation and significantly enhance gas recovery in a low-permeability reservoir when using multiple-well systems.