Properties Of Gas Hydrates Research Articles

A comprehensive review on the geomechanical properties of gas hydrate bearing sediments

Abstract Natural gas hydrates (NGH) that form in sediments beneath the ocean beds are a potential source to meet growing global energy demand. Gas hydrate bearing sediments (GHBS) exhibit improved geomechanical properties (viz., shear strength, stiffness, compressibility, and Poisson's ratio) that are responsible for their greater stability as compared to the native sediments. However, dissociation of gas hydrates during extraction of gas, instability in the GHBS could trigger submarine slope failures, seabed subsidence, and failure of the foundations of seafloor installations. In order to reduce the risk of occurrence of such geohazards, it is imperative to ascertain the stability of GHBS by understanding the variations in their geomechanical properties through field and laboratory investigations, which are time consuming and prohibitively expensive for many researchers. With this in view, the present study attempts to decipher the variation of geomechanical properties with respect to various parameters that affect them (viz., hydrate saturation (SH), hydrate morphology, and confining pressure-temperature conditions), by critically synthesizing the existing data in the literature. It has been noticed that the shear strength and stiffness are the major parameters influencing the stability of GHBS and both share power law relationship with SH. Further, it is noticed that the cohesion is the predominant component of the shear strength of GHBS and shows significant improvement for SH values greater than 15–50%. The variability of cohesion and stiffness with respect to SH have been analysed in tandem with the volumetric deformation, during the shearing process, to propose particle level mechanism hypothesis that provides an insight in to the stress-strain behavior of GHBS. The proposed relationships and mechanisms would aid in understanding the behavior and development of improved modeling of geomechanical properties of GHBS.

An in situ method on kinetics of gas hydrates

Gas hydrate formation is a high-risk and common flow assurance problem in subsea oil production plants. The modern strategies to mitigate hydrate formation have switched from thermodynamic inhibition to risk management. In this new mitigation strategy, hydrate formation is allowed as long as it does not lead to plugging of pipelines. Thus, understanding the growth kinetics of gas hydrates plays a critical role in risk management strategies. Here, we report a new accurate and in situ approach to probe the kinetics of gas hydrate formation. This approach is based on the hot-wire method, which probes the thermal properties of the medium surrounding the hot-wire. As the thermal properties of gas hydrate and its initial constituents are different, variation in these properties is used to probe kinetics of hydrate growth front. Through this in situ method, we determine kinetics of cyclopentane hydrate formation in both mixing and flow conditions. The findings show that at ambient pressure and a temperature of 1-2 °C, the hydrate formation rate under mixing condition varies between 1.9 × 10-5 and 3.9 × 10-5 kg m-2 s-1, while in flow condition, this growth rate drops to 4.5 × 10-6 kg m-2 s-1. To our knowledge, this is the first reported growth rate of cyclopentane hydrate. This in situ approach allows us to probe kinetics of hydrate formation where there is no optical access and provides a tool to rationally design risk management strategies for subsea infrastructures.

Terahertz characterization of propane hydrate

We measured the optical and dielectric properties of propane hydrate using THz spectroscopy with a cryostat enabling a temperature range of 20–240 K. An increase in the real parts of the parameters studied was observed with increasing temperatures and frequency, and an analysis showed a local maximum at around 4 THz. The imaginary parts of the optical and dielectric parameters are related mainly to infrared phonon absorption, and increase with both temperature and frequency. We found that the optical and dielectric properties of gas hydrates based on THz-TDS analysis can be discussed using an equation.

Prediction of transient pressure change during natural gas hydrate formation

The increasing demand for fossil fuels and diminishing natural energy reserves have necessitated the exploration of gas hydrates. Gas hydrates find importance in oil and gas industries where the formation and dissociation of gas hydrate become important. Thus, the proper understanding of formation, decomposition and properties of gas hydrates is a required. In this work, a macroscopic kinetic model is analyzed and modified to predict the pressure change with time during the hydrate formation based on the chemical affinity of compounds. With the help of experimental data, the degree of parity of the modified and unmodified models are explained. The dependency of the chemical affinity of the gas hydrate reformers is explained based on the kinetic model validation with the experimental results. The modified model predict the transient pressure during gas hydrate formation with an average absolute error of 3.6%.

Assessing thermodynamic consistency of gas hydrates phase equilibrium data for inhibited systems

Phase equilibrium properties of gas hydrates in the presence of thermodynamic hydrate inhibitors (THIs) like alcohols, glycols, and salts are essential in developing thermodynamic prediction models to identify their physicochemical features and phase behavior for gas production from hydrates and operation of oil/gas production systems. Though a significant amount of experimental data are available in the literature and models have been developed based on those data, a reliable method to assess the thermodynamic consistency of the data has not been established. Here, we provide a rigorous method to assess the thermodynamic consistency of hydrate phase equilibrium data in inhibited systems. Fundamental thermodynamic relations are used to derive the assessment criteria for thermodynamic consistency, including the heat of dissociation for solid hydrate phase and the activity for liquid water. The quantitative assessment of CH4 hydrate + THIs, including salts, glycols, methanol, and amino acids are performed for demonstration, and guidelines on how to assess the thermodynamic consistency are provided.

In situ Raman spectroscopy study of synthetic gas hydrate formed by cold seep flow in the South China Sea

Properties of gas hydrate are commonly investigated in laboratory by simulators or studied using the hydrate samples recovered from permafrost and marine sediments. Here synthetic gas hydrate (SGH) is quickly formed for the first time by fluids and bubbles erupted from the active cold seeps at the Formosa Ridge in the South China Sea (SCS). SGH samples are in situ detected by a Raman insertion probe for gas hydrate (RiP-Gh) which is deployed by the remotely operated vehicle (ROV) Faxian. Both spatial and temporal in situ Raman spectra of the SGH samples are acquired in order to determine the structure and the evolution of the synthetic gas hydrate. Authigenic carbonate debris or other debris serving as nucleation particles, which is found in the in situ Raman spectra of SGH samples for the first time, may be one factor that can promote the formation of synthetic gas hydrate. The gas-water interface demonstrated by the observation results, also contributes to the quick formation of SGH samples, which agrees well with the previous study. In situ Raman spectra of three SGH samples which have been placed on the seafloor for 0 h, 4 h and 21 h respectively are acquired. Laboratory Raman spectra of one sample which has been surprisingly found and recovered after 9840 h (410 days) since formed on the seafloor are also acquired. The Raman spectra of the four SGH samples indicate that the methane large-to-small cage occupancy ratios of the hydrates vary from 1.01 to 1.39, and the ratios of methane large-to-gas of the hydrates increase from 0.53 to 1.55. Overall, our work suggests a new explanation for the quick formation of gas hydrate compared to that in laboratory simulation work, and reveals the evolution of synthetic gas hydrate after quick formation, which provides a new insight for the study of natural gas hydrate.

Changes in Phases and Physical Properties of Gas Hydrates Under Low to High Temperatures and High Pressures and their Implications of Interiors of Icy Bodies

Changes in Phases and Physical Properties of Gas Hydrates Under Low to High Temperatures and High Pressures and their Implications of Interiors of Icy Bodies

Review of Fundamental Properties of Gas Hydrates: Breakout Sessions of the International Workshop on Methane Hydrate Research and Development

The International Workshop on Methane Hydrate (MH) Research and Development (the Fiery Ice Workshop) began in 2001 with the goal of promoting laboratory and field research collaborations and providing a forum to share new knowledge on MH pertaining to coastal stability, climate change, and energy. Ten workshops have been held over the past 15 years in different countries. Each workshop has included presentations on national programs and policy areas, and new research, along with breakout sessions that focused on current key topics. Two or three concurrent breakout sessions were conducted twice during each workshop. In this paper, we review the breakout sessions on hydrate fundamental properties with the goal of identifying the major accomplishments and changes in hydrate science and engineering related to determining fundamental MH properties over the past 15 years.

Elasticity and Stability of Clathrate Hydrate: Role of Guest Molecule Motions

Molecular dynamic simulations were performed to determine the elastic constants of carbon dioxide (CO2) and methane (CH4) hydrates at one hundred pressure–temperature data points, respectively. The conditions represent marine sediments and permafrost zones where gas hydrates occur. The shear modulus and Young’s modulus of the CO2 hydrate increase anomalously with increasing temperature, whereas those of the CH4 hydrate decrease regularly with increase in temperature. We ascribe this anomaly to the kinetic behavior of the linear CO2 molecule, especially those in the small cages. The cavity space of the cage limits free rotational motion of the CO2 molecule at low temperature. With increase in temperature, the CO2 molecule can rotate easily, and enhance the stability and rigidity of the CO2 hydrate. Our work provides a key database for the elastic properties of gas hydrates, and molecular insights into stability changes of CO2 hydrate from high temperature of ~5 °C to low decomposition temperature of ~−150 °C.

Analyzing Permeability of the Irregular Porous Media Containing Methane Hydrate using Pore Network Model Combined with CT

Gas hydrate as the 21st century new energy is viewed as prospective energy with clean, smaller pollution, and large storage characteristics. The permeability is a key parameter for gas hydrate production. In this work, pore network models combined with X-ray computed tomography (CT) were proposed to analyze the properties of gas hydrate in porous media. We studied the permeability in porous media, used the different shapes of sand including quartz, dolomite and feldspar. Experimental results show that in these three kinds of sand, the absolute permeability of quartz is the largest, feldspar is minimal. Under the same water saturation, capillary pressure of dolomite is less than quartz; water-phase relative permeability in porous media did not obvious change, while gas phase relative permeability is a big difference. Gas phase relative permeability of dolomite is smaller than the other two kinds of sand with low water saturation. However, under the high water saturation, gas phase relative permeability of dolomite is greater than the other two kinds of sand.

Analysis of the Physical Properties of Hydrate Sediments Recovered from the Pearl River Mouth Basin in the South China Sea: Preliminary Investigation for Gas Hydrate Exploitation

Laboratory based research on the physical properties of gas hydrate hosting sediment matrix was carried out on the non-pressurized hydrate-bearing sediment samples from the Chinese Guangzhou Marine Geological Survey 2 (GMGS2) drilling expedition in the Pearl River Mouth (PRM) basin. Measurements of index properties, surface characteristics, and thermal and mechanical properties were performed on ten sediment cores. The grains were very fine with a mean grain size ranging from 7 to 11 μm throughout all intervals, which provide guidance for the option of a screen system. Based on X-ray Computed Tomography (CT) and SEM images, bioclasts, which could promote hydrate formation, were not found in the PRM basin. However, the flaky clay might be conducive to hydrate formation in pore spaces. The measured sediment thermal conductivities are relatively low compared to those measured at other mines, ranging from 1.3 to 1.45 W/(m·K). This suggests that thermal stimulation may not be a good option for gas production from hydrate-bearing sediments in the PRM basin, and depressurization could exacerbate the problems of gas hydrate reformation and/or ice generation. Therefore, the heat transfer problem needs to be considered when exploiting the natural gas hydrate resource within these areas. In addition, the results of testing the mechanical property indicate the stability of hydrate-bearing sediments decreases with hydrate dissociation, suggesting that a holistic approach should be considered when establishing a drilling platform. Both the heat-transfer characteristic and mechanical property provide the foundation for the establishment of a safe and efficient production technology for utilizing the hydrate resource.

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.

Protocol for Measuring the Thermal Properties of a Supercooled Synthetic Sand-water-gas-methane Hydrate Sample.

Methane hydrates (MHs) are present in large amounts in the ocean floor and permafrost regions. Methane and hydrogen hydrates are being studied as future energy resources and energy storage media. To develop a method for gas production from natural MH-bearing sediments and hydrate-based technologies, it is imperative to understand the thermal properties of gas hydrates. The thermal properties' measurements of samples comprising sand, water, methane, and MH are difficult because the melting heat of MH may affect the measurements. To solve this problem, we performed thermal properties' measurements at supercooled conditions during MH formation. The measurement protocol, calculation method of the saturation change, and tips for thermal constants' analysis of the sample using transient plane source techniques are described here. The effect of the formation heat of MH on measurement is very small because the gas hydrate formation rate is very slow. This measurement method can be applied to the thermal properties of the gas hydrate-water-guest gas system, which contains hydrogen, CO2, and ozone hydrates, because the characteristic low formation rate of gas hydrate is not unique to MH. The key point of this method is the low rate of phase transition of the target material. Hence, this method may be applied to other materials having low phase-transition rates.

Dielectric Method for Diagnosing Formation of Gas Hydrates in Gas Pipelines

Experimental study of low-frequency dependence of the dielectric properties of gas hydrate in the process of growth and dissociation in the range 50- 1000 kHz is conducted. It is found that the dielectric loss tangent maximum value is observed at a frequency of 260 kHz and depends on the amount of gas hydrate in the measuring cell. Comparison of degrees of gas-hydrate formations obtained by two independent methods (PVT-method and dielectric method) showed good agreement. It allows us to offer a simple method of controlling the process gas-hydrate formations in the pipes based the measurement of the dielectric loss tangent at a certain frequency.

3-D numerical modelling of methane hydrate accumulations using PetroMod

Within the German gas hydrate initiative SUGAR, a new 2-D/3-D module simulating the biogenic generation of methane from organic matter and the formation of gas hydrates has been developed and included in the petroleum systems modelling software package PetroMod®. Typically, PetroMod® simulates the thermogenic generation of multiple hydrocarbon components (oil and gas), their migration through geological strata, finally predicting oil and gas accumulations in suitable reservoir formations. We have extended PetroMod® to simulate gas hydrate accumulations in marine and permafrost environments by the implementation of algorithms describing (1) the physical, thermodynamic, and kinetic properties of gas hydrates; and (2) a kinetic continuum model for the microbially mediated, low temperature degradation of particulate organic carbon in sediments. Additionally, the temporal and spatial resolutions of PetroMod® were increased in order to simulate processes on time scales of hundreds of years and within decimetres of spatial extension. In order to validate the abilities of the new hydrate module, we present here results of a theoretical layer-cake model. The simulation runs predict the spatial distribution and evolution in time of the gas hydrate stability field, the generation and migration of thermogenic and biogenic methane gas, and its accumulation as gas hydrates.

The prospects of the application of gases and gas hydrates in cryopreservation

In the present review, we attempt to evaluate the known properties of gas hydrates and gases that form them from the point of view of the mechanisms of cryoinjury and cryoprotection, to consider the publications on the freezing of biological materials in the presence of inert gases, and to assess the prospects of development in this field. For this purpose, we searched for information on the physical properties of gases and gas hydrates, compared the processes that occur during the formation of gas hydrates and water ice, and analyzed the effects of the formation and growth of gas hydrates on the structures of biological objects. We prepared a short review on the biological effects of xenon, krypton, argon, carbon dioxide, hydrogen sulfide, and carbon monoxide with emphasis on hypothermal conditions and the probable application of these properties in cryopreservation technology. The descriptions of the existing experiments on cryopreservation of biological objects using gases are analyzed. Based on the information we found, the most promising directions of work in the field of cryopreservation of biological objects using gases are outlined; potential problems in this field are anticipated.

Impact of Gas Hydrate Formation/Dissociation on Water-in-Crude Oil Emulsion Properties Studied by Dielectric Measurements

The impact of the formation and dissociation of gas hydrates on water-in-crude oil emulsion properties has been studied using a dielectric probe. The probe was mounted in a high-pressure cell that is commonly used to characterize thermodynamic and agglomeration/plugging properties of gas hydrates in crude oil and process water systems. The dielectric measurements proved useful to detect hydrate formation earlier or approximately simultaneously with pressure–volume–temperature (PVT) measurements. The dielectric measurements also provided qualitative information regarding changes in droplet size and emulsion stability. A short-wave infrared (SWIR) camera was used to support the dielectric measurements. Live crude oils and associated process waters from North Sea oil fields were used in the experiments.

Properties of gas hydrates formed by nonequilibrium condensation of molecular beams

Low-temperature crystallization of amorphous materials has been analyzed theoretically taking into account nonstationary nucleation. The kinetics of crystallization of amorphous water layers, formed by depositing molecular beams on a substrate cooled by liquid nitrogen, has been investigated by differential thermal analysis. The conditions of gas hydrate formation in low-temperature amorphous-ice layers saturated with carbon dioxide have been studied. The glass-transition and crystallization temperatures of the gas hydrates have been determined from the change in dielectric properties upon heating. Under the deep-metastability conditions, crystallization of water-gas layers leads to the formation of crystallohydrates. Gas molecules are captured by the avalanche-like nucleation of crystallization centers and, therefore, are not displaced by the moving crystal-melt interface. Gas-hydrate samples formed in nonequilibrium water-gas layers are convenient for studying their thermophysical properties.

The experience of mapping of Baikal subsurface gas hydrates and gas recovery

Lake Baikal is the only fresh-water lake where natural gas hydrate accumulations were found in sediments. For the recent decade, Baikal has become a natural laboratory for investigation of the properties of gas hydrates, their indicators, and recovery of gas from subsurface (subbottom) gas hydrates. We present the main results of subsurface gas hydrate mapping and gas recovery test near the delta of the Goloustnaya River.

The status of natural gas hydrate research in China: A review

Over the past century, fossil fuels have provided the majority of China's energy. However, their extensive utilization leads to a shortage and environmental pollution. Recently, submarine and permafrost gas hydrate deposits have been investigated as a possible clean and sustainable energy source by governmental institutions, research organizations, and energy industries in China. The primary objective of this paper is to review the potential studies pertaining to gas hydrate exploration and resource assessment, the safe and efficient exploitation of gas hydrates and the basic properties of gas hydrates. To date, there are over 20 institutions and organizations in China committed to gas hydrate investigation, among which the Guangzhou Marine Geological Survey (GMGS) and the Chinese Academy of Geological Sciences (CAGS) etc. primarily focus on gas hydrate exploration research, while the China National Offshore Oil Corporation (CNOOC) Research Center, Guangzhou Institute of Energy Conversion (GIEC) and China University of Petroleum-Beijing (CUPB) etc. concentrate on gas hydrate mining technologies. In this paper, the occurrence and exploration of gas hydrates in both permafrost regions and the continental slope of China have been determined from numerous research contributions and are presented. Moreover, the latest progress in gas hydrate fundamental studies, including hydrate phase equilibria, hydrate formation mechanisms, hydrate thermal physical properties and the acoustics and resistivity characteristics of gas hydrates are briefly reviewed, and relevant data are gathered and compared. Emphasis is also placed on gas hydrate mining technologies and gas production using depressurization methods, thermal stimulation methods or other methods. Furthermore, the security of natural gas hydrate-bearing sediments during gas production and the environmental impacts of gas hydrate are identified. With additional financial and political support and advanced research facilities, research on gas hydrates in China is progressing rapidly but is still in its early developing stage, thus, future work should be undertaken with greater diligence.