Methane Gas Hydrate: as a Natural Gas Source

Abstract

Gas hydrates, potentially one of the most important energy resources for the future. Methane gas hydrates are increasingly considered a potential energy resource. Enormous reserves of hydrates can be found under continental shelves and on land under permafrost. Methane hydrates are widespread in sea sediments hundreds of meters below the sea floor along the outer continental margins and are also found in Arctic permafrost. Some deposits are close to the ocean floor and at water depths as shallow as 150 m, although at low latitudes they are generally only found below 500 m. The deposits can be 300-600 m thick and cover large horizontal areas. A nearby deposit nearly 500 km in length is found along the Blake Ridge off the coast of NC at depths of 2000-4000 m. Methane gas hydrates of interest primarily for 3 reasons: (1) Gas from hydrate may be a new clean energy source. It is now recognized that there are huge amounts of natural gas, mainly methane, tied up in gas hydrate globally. Methane gas hydrates are a potential energy resource, (2) Natural gas hydrate may play a role in climate change. Methane is a strong greenhouse gas so its escape to the atmosphere from natural gas hydrate could result in global warming, and (3) there are important production problems. Gas hydrate is a hazard in conventional hydrocarbon exploration, from shallow gas release and from seafloor instability, especially in the arctic and in deep water where hydrate is stable. Hydrates may affect climate because when warmed or depressurized, they decompose and dissociate into water and methane gas, one of the greenhouse gases that warms the planet. Methane is a greenhouse gas. Discharge of large amounts of methane into the atmosphere would cause global warming. Methane hydrates hold the danger of natural hazards associated with sea floor stability, release of methane to ocean and atmosphere, and gas hydrates disturbed during drilling pose a safety problem. Continental slope instability caused by hydrate decomposition is suggested as a trigger mechanism for underwater landslides and tsunami generation. If large volumes of methane are stored in marine reservoirs, they may significantly influence the sedimentary environment in which they occur. Methane hydrates are located in the shallow submarine geo-sphere, which is a finely balanced system in equilibrium with all its components such as sediment, pore-water, fluid flows, pressure, temperature, overlying water, hydrate etc. Removal of any one component of this equilibrium may destabilize the whole system leading to irreparable damage. The destabilizing factors may be either natural perturbations or perturbations associated with exploitation. Studies have indicated that methane hydrates have the potential to affect global climate and the geological environment at a catastrophic scale. Methane hydrates are common in sediments deposited high latitude continental shelves and at the slope and rise of continental margins with high bioproductivity. High biological production provides the organic matter buried in the sediment, which during early diagenesis and after exhausting oxygen, sulfate and other electron acceptors, eventually generates methane through fermentative decomposition and/or microbial carbonate reduction. The properties of sediment-hosted gas hydrates are strongly determined by texture, structure, and permeability of the sediment and the mode of supply of methane. © Springer 2010.