A novel high-pressure apparatus to study hydrate–sediment interactions

Hydrates formed from methane and water over thousands of years under both gas-lean (single phase) and gas-rich (two-phase) conditions are commonly present in marine sediments. Several factors such as dissolved minerals in seawater, mineral content, and pore size of sediments are thought to affect hydrate growth. There is much interest in exploiting this energy source, but there are many unknown aspects that need to be addressed. In order to develop or improve methane recovery methods, it is important to be able to mimic natural conditions in a laboratory and study dynamics of methane hydrates in host sediments. To date, a large data set from laboratory studies is available for pure methane hydrates for which kinetic models have been proposed but reproducible data collection in the presence of sediments has proved challenging. We describe herein a new experimental apparatus named FISH (Flexible Integrated Study of Hydrates) that has been designed to confine artificial and natural sediments in a pressure vessel and mimic oceanic conditions in order to study kinetics of methane hydrate formation/ decomposition in these sediments. The unit: 1) consists of a pressure vessel equipped with a first-of-its-kind viewport that is large enough to observe macroscopic hydrate behavior, 2) configuration allows convenient interchangeability of different volume pressure vessels, 3) can accept acoustic probes, and 4) holds multiple sensors for operation under precise pressure and temperature conditions. The unit set up, operation, and preliminary results for experiments with a pressure vessel in which the effective gas to liquid volume (Vg/Vl) ratio was 1.86, are described. The availability of accurate data on the formation/ decomposition cycle and acoustic properties of hydrates will aid in developing a much sought after economical method to extract methane from this vast resource.