Marine gas hydrates

Abstract

Methane and other low-molecular-weight gases, such as ethane and carbon dioxide, can combine with water to form ice-like substances at high pressure or low temperature in what are known as gas hydrates. The stability of these compounds is controlled by several factors including pressure, temperature, salinity, and gas concentrations. Gas hydrates are commonly imaged by the presence of a bottom-simulating reflector in the seismic records, which is the most common tool for identifying hydrate-bearing sediments. Other geophysical tools and borehole logging strategies are used to characterize the presence, distribution, and abundance of these deposits. These techniques are calibrated against geochemical proxies that include pore fluid freshening by gas hydrate dissociation during conventional core recovery and controlled depressurization experiments from pressure cores. Interest in gas hydrate rises from their role in carbon cycling, potential climate effects, and energy considerations. They constitute a large carbon reservoir, and sand-hosted deposits are currently being explored for economic uses, with one of the most innovative approaches being the CO2 for methane exchange.