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ABSTRACT

The estimated amount of gas in the hydrate accumulations of the world greatly exceeds the volume of known conventional gas reserves.  However, the role that gas hydrates will play in contributing to the world’s energy requirements will depend ultimately on the availability of sufficient gas hydrate resources and the “cost” to extract them.  Yet considerable uncertainty and disagreement prevails concerning the world’s gas hydrate resources.

Gas hydrates occur in sedimentary deposits under conditions of pressure and temperature present in permafrost regions and beneath the sea in outer continental margins.  The combined information from Arctic gas-hydrate studies shows that, in permafrost regions, gas hydrates may exist at subsurface depths ranging from about 130 to 2,000 m.  The presence of gas hydrates in offshore continental margins has been inferred mainly from anomalous seismic reflectors known as bottom-simulating reflectors, that have been mapped at depths below the sea floor ranging from about 100 to 1,100 m.  Current estimates of the amount of gas in the world’s marine and permafrost gas hydrate accumulations are in rough accord at about 20,000 trillion cubic meters.

Gas hydrate as an energy commodity is often grouped with other unconventional hydrocarbon resources.  In most cases, the evolution of a non-producible unconventional resource to a producible energy resource has relied on significant capital investment and technology development.  To evaluate the energy resource potential of gas hydrates, will also require the support of sustained research and development programs.

Despite the fact that relatively little is known about the ultimate resource potential of natural gas hydrates, it is certain that gas hydrates are a vast storehouse of natural gas and significant technical challenges need to be met before this enormous resource can be considered an economically producible reserve.

INTRODUCTION

The discovery of large gas hydrate accumulations in terrestrial permafrost regions of the Arctic and beneath the sea along the outer continental margins of the world's oceans has heightened interest in gas hydrates as a possible energy resource.  However, significant to potentially insurmountable technical issues need to be resolved before gas hydrates can be considered a viable option for affordable supplies of natural gas.

Disagreements over fundamental issues such as volume of gas stored within delineated gas hydrate accumulations and the concentration of gas hydrates within hydrate-bearing reservoirs have demonstrated that we know very little about gas hydrates.  Recently, however, several countries, including Japan, India, and the United States, have launched ambitious national projects to further examine the resource potential of gas hydrates.  These projects may help answer key questions dealing with the properties of gas hydrate reservoirs, the design of production systems, and, most importantly, the costs and economics of gas hydrate production.

It is proposed in this paper that the evolution of gas hydrates as a viable source of natural gas, like any other unconventional energy resource (e.g., deep gas, shale gas, tight gas sands, and coalbed methane), will follow a predictable path from research and discovery to implementation (Figure 1); however, insurmountable barriers may exist along this pathway.

Today, most of the gas hydrate research community is focused on three fundamental issues: WHERE do gas hydrates occur, HOW do gas hydrates occur in nature, and WHY do gas hydrates occur in a particular setting.  However, relatively little has been done to integrate these distinct research topics or evaluate how collectively they affect the ultimate resource potential of gas hydrates.  Only after understanding the fundamental aspects of WHERE-HOW-WHY gas hydrates occur in nature will we be able to make accurate estimates of how much gas is trapped within the gas hydrate accumulations of the world.  Even with the confirmation that gas hydrates may exist in considerable volumes, significant technical, economic, and political issues need to be resolved before gas hydrates can be considered a viable energy resource.

In this paper, I have attempted to review the status of gas hydrates as a future energy resource.  The technical and non-technical factors controlling the ultimate resource potential of gas hydrates have been identified and assessed.  The fundamental questions of WHERE do gas hydrates occur, HOW do gas hydrates occur in nature, and WHY do gas hydrates occur in a particular setting have been individually reviewed and discussed.  In addition, published gas hydrate volume assessments have been summarized and the production technology needed to extract the world’s gas hydrate resources are assessed.  The paper concludes with a discussion of the economic and political motivations that may eventually lead to gas hydrate production.  However, before proceeding with the assessment of the future energy resource potential of gas hydrates, this paper begins with a technical overview of gas hydrate physical properties and a review of four relatively well characterized gas hydrate accumulations