U. S. Department of Energy Gas Hydrate Research Impacting Offshore Development
Authors: Allison E.C. 
Published: October 2008

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, anduse 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 deposits1.

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, anduse hydrates to transport gas.