This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 114163, "Toward Production From Gas Hydrates: Current Status, Assessment of Resources, and Model- Based Evaluation of Technology and Potential," by George J. Moridis, SPE, Lawrence Berkeley National Laboratory; Timothy S. Collett, SPE, US Geological Survey; Ray Boswell, US Department of Energy; M. Kurihara, SPE, Japan Oil Engineering Company; Matthew T. Reagan, SPE, Lawrence Berkeley National Laboratory; and Carolyn Koh and E. Dendy Sloan, SPE, Colorado School of Mines, prepared for the 2008 SPE Unconventional Reservoirs Conference, Keystone, Colorado, 10–12 February. The paper has not been peer reviewed.

Gas hydrates are a vast energy resource with global distribution in the permafrost and in the oceans. Even if conservative estimates are considered and only a small fraction is recoverable, the size of the resource is so large that it requires evaluation as a potential energy source. This review paper discusses the distribution of natural-gas-hydrate accumulations, the status of the primary international R&D programs, and the remaining science and technology challenges facing commercialization of production.

Introduction

Gas hydrates are solid crystalline compounds in which gas molecules (referred to as guests) occupy the lattices of ice-like crystal structures called hosts. Hydrate deposits occur in two geographic settings where the necessary conditions of low temperature and high pressure exist for their formation and stability: in the permafrost and in deep ocean sediments.

Most naturally occurring hydrocarbon-gas hydrates contain CH4 in overwhelming abundance. Simple CH4 hydrates concentrate methane volumetrically by a factor of 164 when compared to standard-temperature/-pressure conditions. Some modeling suggests that the energy needed for dissociation could be less than 15% of the recovered energy. Natural-gas hydrates also can contain other hydrocarbons (alkanes), but may also comprise lesser amounts of other gases (mainly CO2, H2S, or N2). The full-length paper contains the complete review.

Occurrence, Research Activities and Priorities, and Prospective Production Targets

Knowledge of the occurrence of in-situ gas hydrates is incomplete and is obtained from both indirect and direct evidence. There are 23 locations with irrefutable evidence of hydrates (direct recovery of hydrate samples): three in permafrost regions and 20 in ocean environments. In permafrost regions, evidence of gas hydrates is provided from two ongoing R&D programs and from analysis of industry 3D-seismic data and data obtained during the drilling and logging of conventional oil and gas wells. The ability to prospect for gas-hydrate deposits by use of these data was demonstrated in the Prudhoe Bay region of the Alaska North Slope. In the marine environment, most data supporting the interpretation of gas hydrates are indirect indicators (such as bottom-simulating reflections) on relatively low-quality 2D-seismic data. However, direct gas-hydrate detection and characterization from marine 3D data have been shown, and the use of four-component ocean-bottom seismic also shows great promise.

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