Modeling, analysis and simulation: methane hydrate in the subsurface

Sand production evaluation during gas production from natural gas hydrates

Progress and challenges on gas production from natural gas hydrate-bearing sediment

Methane hydrates as potential energy resource: Part 1 – Importance, resource and recovery facilities

Interest in natural gas hydrate is increasing rapidly as the multiple implications of its presence in the shallow geosphere are being recognized. The large amount of hydrate methane that is sequestered in shallow terrestrial and marine sediments makes this methane an attractive target for those concerned about future energy requirements and resources. The fact that natural gas hydrate is metastable and affected by changes in pressure and temperature makes any released methane an attractive agent that could globally affect oceanic and atmospheric chemistry and ultimately global climate. And finally this characteristic of metastability could explain ma or seafloor instabilities resulting in submarine slides and slope failures. Thus these ramifications of natural gas-hydrate occurrence all have potential effects on future human welfare, and hence explain the increasing worldwide interest. This chapter introduces natural gas hydrate, provides a background for understanding its occurrence, relates the early history of discovery, and describes the hydrate gas compositions that have been found. Following chapters will deal with the important aspects of natural gas hydrate as a potential (a) energy resource, (b) factor in global change, and (c) submarine geohazard.KeywordsMethane ContentOceanic SedimentMethane HydrateMackenzie DeltaCore CatcherThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Investigation of creep and transport mechanisms of CO2 fracturing within natural gas hydrates

Natural gas hydrates (NGH) are crystalline compounds that consist of water and natural gas (NG) molecules. By hydrogen bonds, water molecules form a regular lattice structure containing many cavities. NG molecules occupy the cavities, and therefore stabilize the cavities. NGH are considered to be one of the most potential alternative world energy resources. The applications of NGH in other fields, such as NG purification, storage, and transportation, are also possible. To obtain the full benefits of all the possible applications of NGH, a full understanding of the kinetics of NGH formation is needed.;Strictly speaking, the experimental works of reproducible intrinsic chemical reaction rate constants of NGH formations have not yet been reported. It has been because the control of the interfacial surface areas among the three phases of gas, liquid, and solid involved in the reaction, i.e. NG in gas phase, water in liquid phase, and NGH in solid phase was experimentally difficult during the progress of water-NG conversion into NGH.;In this dissertation, a new experimental method and analysis to determine the intrinsic reaction rate constants of methane gas hydrate (MGH) and propane gas hydrate (PGH) formations are reported. The important aspect of the novel experimental method is the control on the interfacial surface area in the heterogeneous reacting system. The control was achieved using a well-defined specific particle packing structure consisting of spherical, uniform-sized inert particles (e.g. glass beads). The defined packing structure gave reproducible interfacial boundary area of the heterogeneous reacting systems, and the interfacial boundary area can be modeled using simple geometry.;Data showed that initial pressures and glass bead sizes did not affect the reaction rate constants. The data gave the value of K = (1.89 +/- 0.16) x 10-6 m/s for MGH formation and K = (2.25 +/- 0.53) x 10-6 m/s for PGH formation. Compared to the mass transfer coefficients of methane/propane in water (l) film kL (approximately 10 -5 m/s), the values of K are significantly smaller for both MGH and PGH formations. Hence, the intrinsic reaction rate constants (kr) of MGH and PGH formations were practically represented by the observed K.

Natural gas hydrate is regarded as a kind of potential alternative energy resource and attracts the attention all over the world. Geological surveys have found that most natural gas hydrates are buried at the bottom of the sea. Several development methods, such as depressurization, thermal stimulation and inhibitor injection are proposed gradually on the basis of hydrate special properties, obtaining certain trial-produce performance. It is of great significance to learn the flow rules underground for production safety guarantee and efficiency improvement. However, the special phase transition of hydrate between solid and fluid accompanied by energy and mass change makes it difficult to predict and describe the parameters variations during hydrate-bearing exploitation. Since the hydrate is always sensitive to surrounding conditions, the disturbance of ambient pressure and temperature can change the corresponding phase equilibrium temperature, pressure and even phase transition rate. On the one hand, hydrate dissociation/reformation is an endothermic/exothermic reaction and releases/consumes large amount of gas in the limited space, reacting on the ambient pressure and temperature. On the other hand, hydrate phase transition also induces particles (hydrate, ice, sand, etc.) separation, aggregation and migration, altering the original hydrate saturation, reservoir properties (thermal conductance, permeability, skeleton structure, bonding strength, etc.) and multiphase flow. Then the heat and mass transfer in porous medium driven by the pressure difference and temperature difference influences the ambient conditions. Therefore, it is a complex coupled process with a series of variables. In this research, interaction mechanism between hydrate phase transition and porous media properties has been analyzed through influencing factors and the coupled relationship between multi-fields (containing temperature field, pressure field and seepage field) has been obtained. Taking the deepwater characters into consideration, the wellbore temperature and pressure distribution has been predicted by numerical simulation firstly as the boundary conditions of neighborhood hydrate-bearing reservoir. After proposing assumptions for simplification, the multi-flow model in hydrate- bearing reservoir has been built. Then applying production data referred from existed literatures and field reports, the multi-fields coupled variations during exploitation of hydrate-bearing reservoir have been simulated by the multi-flow model. The results indicated that although the temperature gradient of sea water reduce the wellbore temperature and the pressure gradient increase the wellbore pressure gradually, the ambient conditions are still disturbed significantly and become closer to hydrate phase transition requirements (10~30 MPa, 10~60℃). The near- wellbore temperature increases and pressure decreases earliest, and the variation area spreads towards the further reservoir. As time goes on, the disturbed zone becomes larger and larger but spread rate becomes lower and lower. Combining the reservoir temperature and pressure distributions with the hydrate phase equilibrium, corresponding hydrate phase transition can be analyzed and natural gas production can be estimated, providing a certain theory support for deepwater hydrate-bearing reservoir multi-fields prediction and efficient production.

Efficient back analysis of multiphysics processes of gas hydrate production through artificial intelligence

Methane hydrate formation in clay mineral suspensions containing glycine: Experimental study and molecular dynamics simulation

It is generally accepted that the amount of gas in the world's gas hydrate accumulations exceed the volume of known conventional gas resources. Researchers have long speculated that gas hydrates could eventually be a commercial producible energy resource yet technical and economic hurdles have historically made gas hydrate development a distant goal rather than a near-term possibility. This view began to change in recent years with the realization that this unconventional resource could possibly be developed with existing conventional oil and gas production technology. The most significant development was gas hydrate production testing conducted at the Mallik site in Canada's Mackenzie Delta in 2002. The Mallik 2002 Gas Hydrate Production Research Well Program yielded the first modern, fully integrated field study and production test of a natural gas hydrate accumulation. More recently, BP Exploration (Alaska) Inc. with the U.S. Department of Energy and the U.S. Geological Survey have successfully cored, logged, and tested a gas hydrate accumulation on the North Slope of Alaska known as the Mount Elbert Prospect. The Mallik 2002 project along with the Mount Elbert effort has for the first time allowed the rational assessment of the production response of a gas hydrate accumulation. In addition to the gas hydrate production tests in Canada and the US, marine gas hydrate research drilling, coring, and logging expeditions launched by the National gas hydrate programs in Japan, China, South Korea, and India have provided a much deeper appreciation of the geologic controls on the occurrence of gas hydrates. With an increasing number of highly successful gas hydrate field studies, significant progress has been made in addressing some of the key issues on the formation, occurrence, and stability of gas hydrates in nature. This report deals with the assessment of the geologic and engineering factors that control the ultimate resource potential of gas hydrates. This assessment will be conducted mainly though the examination of several of the more successful international gas hydrate research efforts. Introduction Natural gas hydrate is a combination of two common substances, water and natural gas. If these meet under conditions in which pressure is high enough and temperature is low enough, they join to form a gas hydrate. Vast volumes of sediments in the earth's oceans and polar regions are conducive to gas hydrate formation. Numerous research programs have shown that natural gas hydrate is widespread in permafrost regions and beneath the sea in sediments of outer continental margins. Natural gas hydrates, commonly also known as methane hydrates, are clathrates, (from the Greek and Latin words for " cagework??) meaning that " guest?? gas molecule is encaged in a " host?? framework of water molecules. The empty cagework of water is unstable, and requires the presence of encapsulated gas molecules to stabilize the clathrate crystal, at temperatures both above and below the freezing point of water (Figur 1). Chemists have known about gas hydrates for almost 200 years, but mainly as a laboratory curiosity. The petroleum industry began to take an interest in hydrates in the 1930s when gas-hydrate was found plugging natural gas pipelines. The first suggestions that natural gas hydrates might be present in the geosphere can be attributed to Russian scientists (Makogon et al, 1971; Trofimuk et al, 1973; Makogon, 1981), this was confirmed as scientists on deep-sea drilling expeditions discovered that gas hydrates did occur in deepwater sediments along continental margins (Figure 2).

The compact Arctic Ocean region is the last major hydrocarbon frontier areain the Northern Hemisphere and may possibly be the single richest natural gashydrate (NGH) province on Earth. Because of the extreme weathering and erosionconditions associated with the alternating glacial and interglacial conditions, much of the sediment in accessible gas hydrate stability zones (GHSZ) may havethe same well bed-differentiated, coarse grained character of excellent NGHreservoir hosts. These reservoirs are of the same type that may hostconventional hydrocarbon deposits in more deeply buried sediments. Existingindustry exploration techniques have been used to identify potential NGHdrilling targets, and drilling in the northern Gulf of Mexico has validated theexploration technique. The Nankai deposits off SE Japan and the depositsdrilled in the northern Gulf of Mexico are excellent examples of thesand-turbidite continental margin paratype. It is estimated from examples andapplication of NGH petroleum system analysis that over 6,000 Tcf of natural gasin place may be present in NGH-enriched deepwater turbidite sands within deepcontinental shelf and slope sediments of the Arctic Ocean. In addition todeepwater turbidites, which are well known from other continental margin areas, such as the Gulf of Mexico, two other prospective zones may exist in the ArcticOcean. Troughs, which are glacially excavated depressions that generally deepentoward the shelf margins, may host NGH in sediments that are transitionalbetween the deepwater turbidites and continental shelf sedimentation. Concentrations of NGH may also be accessible from isolated outliers, which areupstanding continental crust fragments that are present within the Amerasia andEurasia Basins.

Future global warming due to anthropogenic emissions of greenhouse gases has the potential to destabilize methane clathrates, which are found in permafrost regions and in continental slope sediments worldwide, resulting in the release of methane gas. Since methane is a strong greenhouse gas, this could produce a potentially important positive feedback. Here, the coupled heat transfer and methane destabilization process in oceanic sediments is modeled in a series of one‐dimensional, vertical columns on a 1°×1° global grid. Terrestrial permafrost is divided into 11 columns based on mean annual surface air temperature. Our base case clathrate distribution results in about 24,000 Gt C as methane clathrate in marine sediments and about 800 Gt C in terrestrial sediments, only a small fraction of which could be destabilized by future global warming. Scenarios of anthropogenic CO2 and CH4 emission are used to drive a simple model of the carbon cycle, yielding scenarios of CO2 and CH4 concentration increase. These increases drive a one‐dimensional coupled atmosphere‐ocean climate model. Globally averaged temperature changes as a function of time and ocean depth are used as upper boundary conditions to drive the heat transfer/methane clathrate release models. Three versions of the ocean model are used which result in different temperature perturbations at the sediment‐water interface: a purely diffusive ocean model, an upwelling‐diffusion ocean model with fixed temperature of bottom water formation, and an upwelling‐diffusion ocean model with a feedback between surface temperature and the upwelling velocity. Methane release from clathrate destabilization is added to the anthropogenic CH4 emission, leading to stronger increases in both CH4 and CO2 concentration. Based on a wide variety of parameter input assumptions and anthropogenic emission scenarios, it appears that the potential impact on global warming of methane clathrate destabilization is smaller than the difference in warming between low and medium, or medium and high anthropogenic CO2 emission scenarios, or arising from a factor of two variation in climate sensitivity. Global warming increases by 10–25% compared to the case without clathrate destabilization for our scenarios using what, in many respects, are worst case assumptions.

Strategies for gas production from Class 2 hydrate accumulations by depressurization

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�

In recent years, the exploration and utilization of methane hydrate from permafrost and off-coast regions has become a very hot topic. Aiming at its potential as a vast energy resources in future use, the current study is focused on the low emission extraction and utilization system for oceanic methane hydrate and its economic and technological feasibility. In this study, recent real extraction tests in both China and Japan in 2017 are firstly discussed and compared, where the challenges in production period and production rate are explained. In those tests, depressurization method is used to dissociate the methane hydrate for gas production form the unconsolidated reservoir layers below the seabed. Based on the conditions of Japan, a systematic utilization system is proposed for oceanic methane hydratewhich is consisted of extraction system, power generation system, Carbon Capture and Sequestration (CCS) system and hot fluid injection system. Vertical well systems are adopted in this design and the strategic warming up process is used before depressurization extraction, so as to obtain optimal production rate of methane gas. The inclusion of CCS makes it possible to utilize methane hydrate with very low carbon emission. It is estimated that the electricity price obtained by this system can be comparable with the current civil electric price in Japan if the production rate is around 1.0×105 m3/d. Also in this study, the real extraction scenarios and possible strategies of Nankai Trough in Japan and Shenhu Area in China are re-visited and discussed by numerical models. It is found that the only depressurization or thermal stimulation method have the problems of wellbore deformation, pressure problem and energy efficiency problems, while combined strategic modes show the possibility of long-term continuous production. For the basic dissociation parameter analysis, the conditions near the equilibrium curve show higher production rate, which is due to higher initial reservoir temperature. Such results indicate the importance of heat supply inside the reservoir layer as the methane hydrate dissociation is endothermic. It is shown that with the increase of reservoir pressure, such temperature effects become more critical as the optimal initial temperature increases according to equilibrium curve. This results support the system design with strategic warming-up process in a sister well during methane hydrate extraction. In addition, the effects of reservoir layer thermal management, hot reservoir fluid flow effects on the dissociation behaviors are analyzed in this study. For vertical well analysis, the production rates under different permeability parameters show the same trend with real production, which in turn help confirm the in-lab permeability tests. Horizontal well simulation show the importance of overburden and under burden. If the confining layers are less permeable, the production rate becomes higher due to the limited intrusive water flow from the confining layers. In sum, this study summarized the advantages and disadvantages of oceanic methane hydrate extraction/utilization methods and put forward a low-carbon emission system. It is hoped that this study will contribute to the future development of both production prediction and real extraction tests.