Deep Sea Gas Hydrates: The Energy of the Future? Deep Sea Studies off Vancouver Island

New clean energy sources and global climate change are subjects of much recent discussion. Naturally occurring gas hydrates containing methane may play an important role in both subjects. Hydrates are solid ice-like substances consisting of rigid water molecule cages stabilized by enclosed gas molecules, notably those of hydrocarbons. Gas hydrate is well known to gas pipelines engineers through its potential for building on the pipe wall and finally blocking flow. It is also known as a hazard in Arctic drilling; a serious shallow blowout occurred due to hydrate in early Mackenzie Delta drilling. It has recently been recognized that natural hydrates occur extensively beneath the deep sea floor of some continental slopes and Arctic land areas. The total gas contained in hydrates globally is estimated to exceed all other recognized sources, which highlights the future energy potential, and because methane is a strong greenhouse gas if released to the atmosphere, the possible role of gas hydrate in global climate. Japan has initiated a major research program to estimate the amount of hydrate beneath the deep sea off Japan and the feasibility of production. Some gas from hydrate has been produced in northern Russia. The Geological Survey of Canada has small programs to evaluate the occurrence of hydrate in both the Arctic and on the continental slope off the west coast. This study deals with the west coast deep sea occurrence.

The presence of gas hydrate is dependent upon both available gas and the appropriate pressure-temperature conditions for stability. Off the coast of Vancouver Island hydrate is stable and adequate gas appears to be present beneath much of the continental slope in water deeper than about 800 m (it is not stable beneath the continental shelf). Most of the gas appears to be biogenic methane produced in the young clastic sediments of the subduction zone accretionary prism (fold and thrust belt). The hydrate occurs mainly in a layer near the base of the stability field about 300 metres below the seafloor. The hydrate is underlain by a layer of low concentration free gas. The detection of hydrate is primarily through a strong seismic reflector called a "bottom-simulating reflector" or BSR that parallels the seafloor marking the contact between the hydrate and underlying free gas. Seismic studies and drilling as part of Canadian membership in the International Ocean Drilling Program (ODP) off Vancouver Island have shown hydrate to be present in a layer a few 10s of metres thick 200-300 m below the seafloor over much of the middle continental slope. Hydrate saturation is 5-10%. The total gas on the Vancouver Island continental slope is estimated to be some 10-12 cubic metres or 350 TCF. This represents a 200 year supply at current Canadian consumption rates. This optimistic description is tempered by the fact that no practical method of production has been proposed. Destabilization of the hydrate to form gas is possible by reducing the pressure, by increasing the temperature or by adding chemical antifreeze. However, the gas density is low, permeability is low, and there is substantial dissociation latent heat to be overcome. New innovative ideas are needed if this resource potential is to be realized.