Following the recent successful test extraction of gas hydrates in the South China Sea, fresh efforts are underway to develop equipment and facilities in a move towards commercial exploitation of this vast reserve of future energy source.
Conventional subsea drilling and production of oil & gas has been matured over more than three decades, it is expected that a lot of the technologies, including hardware, methods and knowhow, can be adapted for deepwater seabed gas hydrates production. This is already demonstrated by the fact that the afore-mentioned China test was conducted by a modern drilling vessel taking a break from her usual oil & gas exploration duties.
Subsea trees are routinely used for controlling production from gas fields; this paper explores the potential adaptation of such a tree for producing gas evolved from hydrates.
Functionality of subsea trees, in both vertical and horizontal formats, is first explained. Considering the special requirements for gas hydrates, such as heating and handling water as a by-product, a concept is then developed for a gas hydrates production tree. The important additional features of the new tree and their practical implementation are discussed, together with future work required.
Gas hydrates are found both onshore and offshore - under the Arctic permafrost and in ocean sediments along nearly every continental shelf in the world. It is believed these gas hydrates deposits combine to be a larger hydrocarbon resource than all the world's oil, natural gas and coal resources put together. This helps explain the serious interests shown in gas hydrates as the answer to meet our future energy needs.
Development work towards commercial exploitation of gas hydrates as a fresh source of energy is gaining momentum amongst university and industrial researchers alike.
Much experience can be gained from the offshore oil & gas drilling and production technologies that have been developed over at least the last 60 years. Furthermore, gas hydrates reserves are found in water depths no less than 500m, usually many times deeper, as increasing water column creating higher pressure and colder temperature at the seabed are conditions necessary for their formation. The extraction of gas hydrates therefore calls for ‘deepwater’ expertise revolving around floating platforms and subsea production facilities.
