FROZEN HEAT | Volume 2

2.1 INTRODUCTION

Gas hydrates occur broadly throughout Earth’s deep-water continental margins and in areas overlain by thick perma- frost (see Volume 1 Chapter 1). They represent a massive nat- ural storehouse of methane gas and hold significant poten- tial as a future energy resource. Though no commercial-scale extraction of methane from gas hydrates has yet occurred, developing the necessary tools and techniques appears plau- sible given recent advances in hydrocarbon recovery capa- bilities. For example a number of previously inaccessible hydrocarbon resources are now being tapped – reservoirs 9 000 metres deep and in 2 500 metres of water (Cunha et al. 2009) and gas trapped in deep shale formations once thought to be unproduceable. However, as with any component of the global energy re- source base, gas hydrates do not occur in the same manner everywhere. Some deposits, due to the nature of their geo- logic settings, will be more promising targets than others. A number of highly variable and location-specific factors in- fluence the nature and development potential of gas hydrate reservoirs. These include the local supply of methane gas, the

configuration of pathways for gas to migrate and concentrate, the presence and extent of the zone in which pressure-tem- perature conditions allow gas hydrates to form, the nature and properties of the host sediments and their capacity to hold rich accumulations, and the regional geology that pro- vided the time and conditions for gas hydrates to form and to persist as significant accumulations. Because these factors vary significantly, even at a local scale, gas hydrate occurrenc- es are highly variable (Fig. 2.1). Therefore, while it is likely that Earth contains enormous volumes of methane within gas hydrates, it is also likely that only a small percentage of that gas exists in a manner that makes extraction technically and/or economically feasible, at least in the relatively near future (Text Box 2.1). This chapter reviews some key issues in understanding the energy supply potential of gas hydrates. We discuss the best- studied sites where gas hydrates have been evaluated, rang- ing from the most promising sites to the most problematic. Then, in Chapter 3, we discuss the leading means by which these reservoirs might be produced.

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