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Abstract Gas hydrates are frozen cage-like solids in which water molecules enclose gas molecules. Hydrates form under high pressure at temperatures near freezing in ocean sediments and arctic permafrost. Gas Hydrates, although not likely to become an economic natural gas resource for many years, have the potential to radically alter the balance of world energy. This paper will summarize the status and expected future directions for research to:quantify and characterize the resource, assess the producibility of hydrate deposits, understand the potential impact of hydrates on safety and seafloor stability for structures in areas underlain by hydrates, define the potential impacts of hydrates on global climate change, and use hydrates to transport gas. Introduction Gas hydrates are frozen cage-like solids in which water molecules enclose gas molecules. Hydrates form under high pressure at temperatures near freezing in ocean sediments and Arctic permafrost. Fig. 1 shows the conditions favorable to gas hydrate formation in marine and permafrost settings. In the ocean, hydrates form in subsea sediments and underlying formations at water depths greater than about 1100 feet. In the arctic, hydrates are stable below permafrost starting at depths of about 600 feet. In all locations, the bottom of the hydrate stability zone is limited by increasing geothermal temperatures at depth. The ice-like materials store immense amounts of gas B 160 cubic feet of gas at surface conditions can be contained in a cubic foot of hydrates. Gas hydrates represent the largest accumulations of natural gas on Earth; the energy potential in the methane in these deposits may be at least twice the amount of energy in all known coal, crude oil, and natural gas deposits. Gas Hydrates, although not likely to become an economic natural gas resource for ten to twenty years, have the potential to radically alter the balance of world energy. Countries that do not have other indigenous hydrocarbon resources, most notably Japan and India, are expected to develop commercial production of hydrates much sooner than the United States. Japan National Oil Company will drill several wells in the Nankai Trough, about 40 miles south of Japan, in 2000 to test hydrate zones, which they hope will lead to commercial produciton of methane within ten years. In the nearer term, solution of potential hydrate problems impacting offshore operations is necessary as companies move into Gulf of Mexico deepwater areas underlain by hydrates. In addition, understanding the volume and flux of carbon in hydrates is important in making decisions about future resource development and carbon management. Recently, the use of hydrates to transport remote gas has gained attention as a possibly safer and more energy efficient method than Liquefied Natural Gas (LNG.) This paper will summarize the status and expected future directions for research to:quantify and characterize the resource, assess the producibility of hydrate deposits, understand the potential impact of hydrates on safety and seafloor stability for structures in areas underlain by hydrates, define the potential impacts of hydrates on global climate change, and use hydrates to transport gas.
Lapshin, Victor D. (Far Eastern Federal University) | Slesarenko, Vacheslav V. (Far Eastern Federal University) | Morozov, Alexey A. (Far Eastern Federal University) | Solomennik, Sergey F. (Far Eastern Federal University)
The main reserves of methane on our planet are in the form of gas hydrate and more than 90% of them are at the bottom of the oceans. Scientists in many countries are making active efforts to establish effective technology for the development of gas hydrate deposits and, primarily located in the sedimentary rocks of the ocean floor. However, the first experience indicates that the development costs of gas hydrate deposits are very high. One of the main reasons for the high cost of recovering methane hydrate is the high value of the decomposition’s thermal effect. The heat of methane hydrate decomposition is 410 kJ/kg, that 30% exceeds, even energy intensive process, as the melting water ice. We have proposed and patented the way to develop marine gas hydrate deposits without the cost of thermal energy and using of any environmentally hazardous substances.
The method consists in grinding of sediment filled of methane hydrate and its subsequent lifting platform by the pipeline in the form of a suspension in seawater. When lifting the hydrate-contained suspension crosses the line of phase equilibrium and goes out of his stable thermodynamic state. Decomposition of gas hydrate phase in this case will be provided at the expense of the sea water crystallization energy. In the pipeline the conversion of gas hydrate slurry in the slurry containing of water, ice particles and gas, released from gas hydrate happen. It should be noted that the methane gas released from the hydrate, creates a lifting force in the pipe, thus avoiding the energy costs for transporting hydrate-contained rock on the surface.
Wang, Zhiyuan (China University of Petroleum (East China)) | Zhao, Yang (China University of Petroleum (East China)) | Zhang, Jianbo (China University of Petroleum (East China)) | Wang, Xuerui (China University of Petroleum (East China)) | Yu, Jing (China University of Petroleum (East China)) | Sun, Baojiang (China University of Petroleum (East China))
Summary Hydrate-associated problems pose a key concern to the oil and gas industry when moving toward deeper-offshore reservoir development. A better understanding of hydrate-blockage-development behavior can help flow-assurance engineers develop moreeconomical and environmentally friendly hydrate-management strategies for deepwater operations. In this work, a model is proposed to describe the hydrate-blockage-formation behavior in testing tubing during deepwater-gas-well testing. The reliability of the model is verified with drillstem-testing (DST) data. Case studies are performed with the proposed model. They indicate that hydrates form and deposit on the tubing walls, creating a continuously growing hydrate layer, which narrows the tubing, increases the pressure drop, and finally results in conduit blockage. The hydrate-layer thickness is nonuniform. At some places, the hydrate layer grows more quickly, and this is the high-blockage-risk region (HBRR). The HBRR is not located where the lowest ambient temperature is encountered, but rather at the position where maximum subcooling of the produced gas is presented. In the section with a depth from 50 to 350 m, hydrates deposit more rapidly and this is the HBRR. As the water depth increases and/or the gasflow rate decreases, the HBRR becomes deeper. Inhibitors can delay the occurrence of hydrate blockage. The hydrate problems can be handled with a smaller amount of inhibitors during deepwater well-testing operations. This work provides new insights for engineers to develop a new-generation flow-assurance technique to handle hydrate-associated problems during deepwater operations. Introduction Various flow-assurance problems are encountered during deepwater operations, among which hydrates are the leading flow-assurance problem (Sloan 2005).