Abstract

This presentation will provide an overview of predicted methane hydrate deposits in different coastal regions and the advantages of combining different parameters in the evaluation. Work will include data from expeditions in the Gulf of Mexico at Atwater Valley and Alaminos Canyon, on the mid Chilean Margin, west of Concepion, and on the Hikurangi Margin, northeast of New Zealand. Data may be included from a September expedition on the Beaufort Sea. The approach will provide an overview of the benefits and issues with the interpretation of deep sediment hydrate deposits using different approaches for the field survey. This presentation supports combining a variety of parameters for these surveys.

Methane hydrates are recognized to exist in high concentrations in coastal oceans around the world. The Japanese are exploring the potential for hydrates in the Nankai Trough, off the coast of Tokyo Japan, for development as a dominant national energy source. This investigation has lead to Arctic tundra hydrate energy evaluation in the Mackenzie Delta and Prudhoe Bay by international governments, universities and industry. Exploration for the hydrates depends on data from seismic profiling and deep sediment drilling. This approach to hydrate exploration is expensive. Recent studies have combined seismic profiles, shallow sediment geochemistry, heatflow and controlled source electromagnetics to predict deep sediment hydrate deposits. This approach provides a more thorough, less expensive, investigation prior to deep sediment drilling.

NRL has been involved in methane hydrate exploration off the coasts of New Zealand, Chile, Canada and in the Gulf of Mexico. In addition, there are current plans to survey sediment hydrate deposits off the northern coast of Alaska in the Beaufort Sea. These studies have shown a wide variation in the prediction of deep sediment methane hydrate deposits within and between the locations. General findings of these studies are needed for a thorough geochemical evaluation. Strong seismic blanking indicative of high vertical methane migration off the coast of Chile was observed to have a low vertical methane flux through the deep sediment. High vertical methane migration in Atwater Valley in the Gulf of Mexico was observed to be coupled with a high vertical chloride flux in the porewaters, that suggest deep sediment salt diapirs caused unstable sediment methane hydrate deposits. Bottom simulating reflection, coupled with seismic blanking were believe to indicate high vertical methane fluxes on the Hikurangi Margin off the coast of New Zealand. However, shallow sediment geochemical data taken through this region suggested very low deep sediment hydrate deposits.