Fire and Ice: Gas Hydrate Transportation - A Possibility for the Caribbean Region

Thermally efficient production of natural gas can be accomplished by the use of hot brine to dissociate solid gas hydrate deposits in the earth. The advantages of brine stimulation over steam or hot-water injection are lower energy requirements for reservoir heating and hydrate dissociation, reduced heat losses, higher gas production, and improved thermal efficiency. In addition, the problems of blockage of rock pores and wellbore because of reformation of hydrates during gas production can be avoided. A mathematical model for a hot-brine stimulation technique was developed to compute gas recovery and the energy-efficiency ratio (i.e., the ratio of energy content of produced gas to heat injected) for a reservoir containing gas hydrates. The effects of variations in reservoir porosity, hydrate-zone thickness, depth, salinity of brine, brine temperature, and brine injection rate on the energy-efficiency ratio and gas production were determined. A comparison of brine and steam injection cases for the same heat injection rate shows higher gas production and energy-efficiency ratio for the brine case.

Technological paradigm-based development strategy towards natural gas hydrate technology

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 93492, “Gas-Hydrate Production Technology for Natural-Gas Storage and Transportation and CO2 Sequestration,” by R. Masoudi, SPE, and B. Tohidi, SPE, Heriot-Watt U., prepared for the 2005 SPE 14th Middle East Oil & Gas Show and Conference, Bahrain, 12–15 March. Gas hydrates (clathrates) are ice-like crystalline compounds that form under low temperature and elevated pressure conditions. Within the gas-hydrate lattice, water molecules form a network of hydrogen-bonded cage-like structures enclosing the guest molecules that generally comprise low-molecular-diameter gases [e.g., methane, ethane, propane, or carbon dioxide (CO2)]. Although hydrate formation can pose serious flow-assurance problems in the oil and gas industry, gas hydrates present a novel means for gas storage and transportation with potential applications in a wide variety of areas. Introduction The need for natural gas at lower costs is the challenge that drives the development of a new process for storing and transporting natural gas in the form of frozen hydrate. An important property of hydrates that makes them attractive for use in gas storage and transportation is their very high gas-to-solid ratio. In addition to the high gas content, gas hydrates are remarkably stable. When the gas hydrate, which is formed at a high pressure and low temperature, is returned to atmospheric pressure, dissociation begins at the surface and an ice film forms over the water that covers the surface and prevents further hydrate dissociation. This “self-preservation” effect causes the gas hydrate to remain stable at atmospheric pressure. These properties make natural-gas-hydrate (NGH) technology very attractive for natural-gas storage and transportation and CO2 sequestration. Economics For small- to medium-sized gas fields, hydrate technology is an appropriate alternative to the well-established liquefied-natural-gas (LNG) technology. LNG technology is economically feasible only in large-scale projects. Compared to alternative technologies such as LNG and gas to liquids, NGH technology is relatively simple, low cost, and does not require complex processes or pressure and temperature extremes. Capital cost of NGH technology is approximately 25% lower than the capital cost of LNG technology. Hydrate Production There are fundamental interests in continuous production of NGH in a large-scale reactor and effective long-term storage of gas in clathrates. NGH production accounts for more than 60% of the costs of the NGH chain. Development of an efficient technique that is practical and economical for mass production of gas hydrates is vital for realizing NGH technology. There are a number of technical challenges to be addressed in development of a cost-effective NGH production process.

Chapter 12 - Comparisons of field activities in different worldwide sites

Gas Hydrates being projected as the next most important source of energy are object of immense research activity. The study relates to an analytical review of the conditions for the Natural Clathrate formation, production and their use as a source of fuel and gas transportation systems. We look at various production techniques for extraction of vast gas reserves inhibited in these resources. The problem of transportation of natural gas using pressurized hydrates for transportation is one of the highlights. We would like to emphasize the concept of replacement of Methane by Carbon-di-Oxide in the hydrate structure for the purpose of production of free methane from the hydrate bearing zones. The penetration of Carbon-Di-Oxide in the reservoir would be at a rate sufficient for the continuous production and injection of Carbon-di-Oxide and its entrapment helping in reducing global warming effects considering the large area the gas hydrates cover around the world. Transportation of gas in the form of hydrates would help in reducing the huge costs involved in the installation of pipelines and their maintenance and other problems encountered during transportation With the Oil and Natural gas reserves depleting and transportation of the natural gas giving rise to maintenance and installation costs it would be worthwhile to take a look at new production methods for hydrate hydrocarbon production. Introduction Hydrates are solid crystalline compounds formed by non-stoichiometric relations between the host and the guest molecules. The host molecules in most cases being water (although other liquids like Freon-12 are also known to form hydrates) forming cage like structures encompassing the guest molecules which include a variety of known compounds like methane, ethane, carbon-di-oxide. There are three known structures of gas hydrates which exist in nature S-I, S-II and the rare H structure with each structure having its own non-stoichiometric relation between the host and the guest molecules. Structure I gas hydrates contain 46 water molecules per unit cell arranged in 2 dodecahedral voids and 6 tetrakaidecahedral voids, which can accommodate at most 8 guest molecules up to 5.8 Angstroms in diameter. Structure I allows the inclusion of both methane and ethane but not propane. Structure II gas hydrates contain 136 water molecules per unit cell arranged in 16 dodecahedral voids and 8 hexakaidecahedral voids, which can also accommodate up to 24 guest molecules, but to a larger diameter of 6.9 Angstroms. This allows inclusion of propane and iso-butane in addition to methane and ethane. The rare Structure H gas hydrates, which contain 34 water molecules per unit cell arranged in 3 pentagonal dodecahedral voids, 2 irregular dodecahedral voids, and 1 icosahedral void, can accommodate even larger guest molecules such as iso-pentane.1 The type of structure and their geometry defines the various properties of the substructure of the formation as the gas hydrates are known to have a substantial role in the mechanical strength of the formations they are found. Gas hydrates occur in regions where the conditions are ideal for their development and can rapidly form or deteriorate depending upon shift of phase equilibrium for their formation and hence the study of various equilibrium conditions for gas hydrates is essential to produce natural gas commercially from them. These studies help us in deciding the production mechanisms and the design criteria for the production systems. Study of different equilibrium conditions leads to a common understanding of three basic requirements for hydrate formation and stability.

Thermodynamic phase equilibria study of Hythane (methane + hydrogen) gas hydrates for enhanced energy storage applications

A hydrate-capped gas reservoir is defined here as a reservoir that consists of a hydrate-bearing layer underlain by a two-phase zone involving mobile gas. In such a reservoir, hydrates at the top contribute to the produced gas stream once the reservoir pressure is reduced by gas production from the free-gas zone. Large gas reservoirs of this type are known to exist in Alaska and Siberia and are expected to exist in the Mackenzie Delta of the Northwest Territories in Canada. Gas production from a hydrate-capped gas reservoir is a process governed by a combination of mechanisms of heat transfer, fluid flow, thermodynamics and kinetics of hydrate decomposition. Using a comprehensive numerical simulator, an extensive simulation study indicates that some of the non-linear processes involved in gas production from hydrate reservoirs (i.e. the convective heat transfer and the kinetics of hydrate decomposition) have a negligible effect on the overall physics of the process. This significantly reduces the complexity of the heat and fluid flow equations and legitimizes the construction and use of simplified models. In this work, we invoke the above approximations and develop a generalized gas material balance equation. This equation has two significant differences from the material-balance equation for conventional gas reservoirs, including the incorporation of:the effect of cooling due to endothermic decomposition of the hydrate; andthe effect of generated gas and water from the hydrate decomposition. In this model, it is assumed that a mobile phase exists in the hydrate zone; thus, no sharp hydrate dissociation interface is assumed. Considering the sensible heat of the hydrate zone and heat transfer from cap and base rocks, the gas and water generation rates are determined on the basis of the equilibrium rate of the decomposition process. Verification of the solution is obtained by comparing results with those of a comprehensive hydrate reservoir numerical simulator. The model developed here can be used as an approximate engineering tool for evaluating the role of hydrates in improving the productivity and extending the life of hydrate-capped gas reservoirs. Introduction Natural gas hydrates are solid molecular compounds of water with natural gas that are formed under certain thermodynamic conditions. There is evidence that enormous amounts of natural gas exist in the form of hydrate deposits in many regions of the world(1). These deposits occur in sub-oceanic sediments as well as in arctic regions. Every unit volume of gas hydrate has the potential to contain 170 to 180 volumes of gas at standard conditions, making the energy content of one cubic metre of a hydrate reservoir more than other types of unconventional gas reservoirs(2). In view of the large untapped resources of natural gas hydrates, extensive research and development work is underway to determine what fraction of this resource is recoverable. A number of recovery processes have been suggested for producing gas from hydrates in sediments. Sloan(3) and Makogan(4) have presented an extensive review of the suggested methods including depressurization, thermal stimulation and inhibitor injection.

Effectively addressing today’s energy challenges requires advanced technologies along with policies that influence economic markets while advancing the public good.

The article considers the modern problems and prospects of the development of technologies of transporting the natural gas by sea due to the fact that gas hydrate deposits are found on the bottom of Lake Baikal, the Black Sea, the Caspian Sea and the Okhotsk Sea. It has been stated that despite the proved gas hydrate deposits the fields have not been explored yet. Introducing the technology for transporting gas by sea in gas hydrate form is being substantiated. Comparative analysis of LNG, CNG and NGH technologies for sea transportation of natural gas proved that the transport component of the NGH technological chain has significant advantages over LNG and CNG technologies. The process of converting thermal energy of the ocean has been proposed to use for increasing the energy efficiency of methane production from subsea gas hydrate deposits in the gas hydrate cycle, which can save 10-15% of the produced methane for electricity generation. A schematic and technological solution of a gas production complex is presented, according to which carbon dioxide is introduced into the gas hydrate layer to extract methane from gas hydrates. To improve the kinetics of replacing methane with carbon dioxide in gas hydrates it is proposed to recycle a portion of CO2. Due to the specific and diversified geographic, economic, political and other conditions the conventional technologies for pipeline transportation of gas and LNG cannot fully meet the requirements of gas export and production projects. It has been inferred that NGH technology is most suitable for solving the problem of diversifying natural gas supplies from the Arctic regions, the Black Sea and in the development of offshore gas and oil fields.

The continued rise in oil prices and environmental concerns have made natural gas (NG) one of the world’s most important energy sources. As populations and economies grow, the demand for natural gas is increasing due to the expansion of the industrial and commercial sectors, as well as increased household incomes. The potential for significant increases in natural gas supply to meet growing demand makes decisions at all strategic, tactical and operational levels necessary in building new or restructuring existing natural gas transportation systems. In this paper, the multi-objective optimization of natural gas hydrate (NGH) transportation is proposed as a tool for supporting regulatory decisions. Three objective functions are involved in the formulation of the problem: minimization of subsidy costs, maximization of energy utilization, and maximization of profit for each NGH plant. As part of the design parameters for the NGH project, the regulatory agency must consider the entrepreneur’s return on investment and the needs of current and future consumers. In the absence of an optimization tool, this problem may result in unfair gas prices or a lack of investor interest. With a continuous increase in natural gas consumption, the proposed analysis examines growing markets. The mixed subsidy mechanism was applied to a typical example in order to demonstrate the performance of the proposed approach.

While liquefied natural gas (LNG) is the dominant technology for marine transport of natural gas, compressed natural gas (CNG) is an economically attractive alternative for transportation of relatively small amounts of natural gas over shortdistances (up to 6 Bcm/year transported over 2000 km, respectively). Because the main capital expenditure in a CNG project is on marine transport vessels, careful design of CNG transport fleets and compatible distribution schedules is important. Design through solution of an all-encompassing optimization problem would be desirable but complicated and intuitive unappealing. In this work, a structured optimization framework is applied to potential marine CNG transport from a source in the Trinidad/Venezuela area to island countries in the Caribbean. Two general patterns emerge in the results: A "hub-andspoke" pattern for servicing of the largest four consumption markets (Puerto Rico, Dominican Republic, Jamaica, and The Bahamas) and a cyclical "milk-run" pattern for the remaining (smaller) markets. Introduction The role of natural gas as a fuel is slated to increase dramatically in the coming decades, owing to the efficiency and environmental friendliness of natural gas in comparison to other fuels. However, transportation of natural gas from points of production to consumption markets remains a challenge. Two well established gas transportation technologies currently dominate the market: Pipeline and liquefied natural gas (LNG) accounting for 70 and 30 percent of transported gas, respectively. Pipelines generally offer the most economically attractive solution and are the preferred choice whenever feasible, such as for land transport. Subsea pipelines are restricted by the distance and terrain they can traverse. As a result, transport of natural gas by sea vessels is favored for transport over long distances spanning sea water. While LNG is currently the dominant technology used for sea transport of natural gas, a number of recent studies have shown that compressed natural gas (CNG) is economically more attractive than LNG for sea transport of relatively small volumes of natural gas over small distances (Marongiu-Porcu, et al., 2008, Wang and Marongiu-Porcu, 2008). In comparison to LNG, which requires costly liquefaction and regasification facilities at the shipping and receiving sites, respectively and is energyintensive, CNG requires minimal investment in facilities at the shipping and receiving sites and uses less energy. The main capital cost for CNG is incurred for transportation vessels. Although the cost for transportation vessels is higher for CNG than for LNG (stemming from corresponding gas compression ratios of 300:1 vs. 600:1, respectively), overall economics favor CNG for short distances and small loads, as summarized in Figure 1. Finally, because the demands for the entire chain of operations to be well coordinated and in place are easier to meet for CNG (compression / transportation / distribution) than for LNG (liquefaction/transportation/regasification), the former provides an additional degree of flexibility that is welcome in situations of changing market conditions. Even though CNG is used widely in land applications (buses, passenger cars) and a proof-of-concept for sea transport of CNG has existed since the 1960s (Broeker, 1969), CNG has yet to make inroads into the transportation market for natural gas. Three factors have contributed towards that. First, investment emphasis internationally has been primarily on LNG, for understandable reasons (see Figure 1). Second, CNG vessel designs and projects have been envisioned to eke a bite out of the LNG pie, which is not necessarily a good approach. Third, innovative CNG vessel designs for low cost and high efficiency have become available only in recent years. There are certainly several regions worldwide whose energy needs, geography, and access to natural gas sources would make them good candidates for application of CNG sea transportation (Figure 2). For each of these regions there exist multiple scenarios for CNG distribution, in terms of number of vessels, vessel capacities, and itineraries. Identification of promising scenarios is necessary to determine project economics and possibly guide future technological developments.

The modern technology for the recovery of helium from heliumcontaining natural gas is based on the lowtemperature separation (fractional distillation) method, in which helium is separated from other gases in the course of their liquefaction. This method requires considerable energy and resource inputs. An energysaving route to separate gas mixtures can be enrichment of natural gas with helium upon clathrate hydrate formation (1). Gas (clathrate) hydrates are inclusion compounds consisting of water molecules, which form the host crystal lattice, and guest molecules occupying lattice cavities (2). Current interest in gas hydrates stems from their possible use as fuel, as well as from their possible effect on global climate changes (3) and the use of gas hydrate technologies for natural gas storage and transportation (4). The helium content in natural gas is usually low as compared with the major component methane, although there are some natural gas deposits contain� ing up to 8 vol % helium. Methane accounts for more than 70-80 vol % of such gas deposits. Commercially interesting for helium recovery are natural gas deposits containing more than 0.3 vol % helium (5). The exist� ence of clathrate helium hydrates is still debatable since no reliable experimental data supporting or refuting this fact have been available so far. However, experimental evidence for the possibility of helium hydrate formation has been reported in (6). It has been theoretically predicted that structure II helium hydrates can form at high pressures (beginning with 800 atm) and low temperatures (250 K) (7). It has been shown that, at the same temperatures, mixed structure I and II methane-helium clathrate hydrates form at lower pressures than pure helium hydrates even at small concentrations of methane in the gas phase (8). The present work is aimed to find a correlation between the composition of mixed methane-helium hydrates of cubic structures I and II and the composi� tion of the gas phase being at equilibrium with the hydrate, as well as to determine conditions of forma� tion of mixed methane-helium hydrates at low helium concentrations in the gas phase for developing meth� ods of deep purification of helium from methane via hydrate formation.

<p>Gas hydrates are potential energy resources which can be formed at low temperature and high pressure. The number of recoverable gas hydrates are limited due to the specific temperature, pressure conditions and technical limitations of gas production. Various production methods have been studied around the world to overcome these technical limitations. Gas production methods from gas hydrates are divided into methods of dissociating gas hydrates and non-dissociating gas hydrates. The dissociation methods including depressurization method, thermal injection method, and chemical inhibitor injection method can decrease in effective stress of the ground due to phase conversion. On the other hand, CH<sub>4</sub>-CO<sub>2 </sub>replacement method is geomechanically stable because it does not dissociate gas hydrates. Also, CH<sub>4</sub>-CO<sub>2 </sub>replacement method has the advantage of sequestering carbon dioxide while producing methane. However, CH<sub>4</sub>-CO<sub>2</sub> replacement method has the disadvantage such as low production efficiency and understanding kinetics of gas production. In this study, soaking, gas permeability of gas hydrate layer and hydrate saturation are considered in order to promote the production efficiency of CH<sub>4</sub>-CO<sub>2</sub> replacement method. Results show that production efficiency increases with the number of soaking process, the higher gas permeability and hydrate saturation. According to the experimental results in this study, the production efficiency can be increased by considering the soaking time, procedure and selecting the proper gas hydrates site.</p><p>Acknowledgement</p><p>This work is supported by the Korea Agency for Infrastructure Technology Advancement(KAIA) grant funded by the Ministry of Land, Infrastructure and Transport (Grant 20CTAP-C152100-02). Also, it is supported by partial funding from NPRP grant # NPRP8-594-2-244 from the Qatar national research fund (a member of Qatar Foundation) and  the Ministry of Trade, Industry, and Energy (MOTIE) through the Project “Gas Hydrate Exploration and Production Study (20-1143)” under the management of the Gas Hydrate Research and Development Organization (GHDO) of Korea and the Korea Institute of Geoscience and Mineral Resources (KIGAM).</p>

Vertical integration between natural gas and power generating companies is essential in ensuring profitable monetisation of the massive natural gas fields in all regions of the world, including the Asia-Pacific. With a simple economic model, major investment drivers most likely to ensure the success of such integration have been highlighted in this study. The sub-surface and surface engineering data inputs into this model were obtained from a natural gas company conducting a test trial of feeding gas into a 14.4-24 MW Power Plant. Data included production profiles, facility costs and historical performance obtained from both gas and power sides of the integrated venture. Also included in the modelling were prevailing regimes of fiscal and government incentives. Adequate measures of economic and risk analyses were implemented. To validate the model, the assumptions were passed through challenge sessions, and many runs of other investment options were made. The outputs were checked for consistency. The results have shown that gas-to-power profitability, and hence final investment decisions, are mostly affected by changes in gas and power market prices. Supply reliability, government interventions, project location, and expected return are the next set of important variables any investor should closely monitor. Natural gas costs and electricity consumption pattern additionally affect the power generation side of the venture. Effectively identifying, evaluating, and communicating these investment drivers should ensure profitable gas field monetisation - in the form of gas-to-power ventures. Project optimisation and effective business control should also be facilitated.

The Importance of Natural Gas Reforming