Well Design Requirements For Deepwater And Arctic Onshore Gas Hydrate Production Wells

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Abstract Gas hydrate wells will have a number of production challenges, including maintaining commercial gas flows with high water production rates; operating with low temperatures and low pressures in the wellbore; flow assurance issues including hydrates and freezing in the wellbore; controlling formation sand production into the wellbore; and ensuring well structural integrity with reservoir subsidence and/or changes in geo-mechanical properties along the wellbore. This paper addresses these production issues and outlines the design requirements for typical deepwater and arctic onshore gas hydrate production wells. Background Methane gas hydrates are solid crystalline compounds of water and methane gas, in which the molecules of methane occupy the lattices of ice-like crystal structures. Methane hydrates can form and accumulate in sandstones, shales, or silts, where methane and water is present under the necessary conditions of low temperature and high pressure, as illustrated in the following figure. Hydrates can occupy the pore spaces of sands and silts, and can also be found in fractures or lenses, and in some cases can act as the matrix supporting sediments. In North America, onshore gas hydrates can be found under permafrost in the US and Canadian Arctic regions, and offshore gas hydrates can be found in the deepwater margins around the continent. Internationally, offshore methane hydrates have been discovered in deepwater margins in many locations around the world. There has been no consistent effort to map and evaluate this resource on a global scale; therefore, current estimates of gas in place volumes vary widely, possibly up to many thousands of TCF (Moridis 2010). Given the sheer magnitude of the resource, ever increasing global energy demand, and the finite volume of conventional fossil fuel reserves, gas hydrates are emerging as a potential energy source for a growing number of nations, even if only a small portion of gas hydrates can be economically recovered. The attractiveness of gas hydrates is further enhanced by the environmental desirability of natural gas as opposed to solid or liquid fuels. Thus, the appeal of gas hydrates accumulations as future hydrocarbon gas sources is rapidly increasing and their production potential clearly demands technical and economic evaluation. The past decade has seen a marked acceleration in gas hydrate research and development.