Microstructure of natural hydrate host sediments

Abstract

There is worldwide interest in the study of natural gas hydrate because of its potential impact on world energy resources, control on seafloor stability, significance as a drilling hazard and probable impact on climate as a reservoir of a major greenhouse gas. Gas hydrates can (a) be free floating in the sediment matrix, (b) contact, but do not cement, existing sediment grains, or (c) actually cement and stiffen the bulk sediment. Seismic surveys, often used to prospect for hydrates over a large area, can provide knowledge of the location of large hydrate concentrations because the hydrates within the sediment pores modify seismic properties. The ability to image a sample at the grain scale and to determine the porosity, permeability and seismic profile is of great interest since these parameters can help in determining the location of hydrates with certainty. We report here on an investigation of the structure of methane hydrate sediments at the grain-size scale using the synchrotron radiation-based computed microtomography (CMT) technique. Work has started on the measurements of the changes occurring as tetrahydrofuran hydrate, a surrogate for methane hydrate, is formed in the sediment.