Methane hydrate reservoirs are different from conventional gas and oil reservoirs. The latter are usually located several kilometres deep in sediments that are millions of years old, and which have been compressed into solid rocks. These deposits are also usually overlain by solid impermeable rock layers. Methane hydrates, on the other hand, are located in much younger and softer sediments. Conventional drilling technology is, for one thing, very expensive, and furthermore, not adapted for the exploitation of gas hydrate deposits in soft sediments. German researchers and industries therefore want to develop a small drilling platform that can be placed on the sea floor, to which the drill, pumps and electrical supply can be attached. Such a system could work independently to a large extent to extract methane from the hydrate deposits. A forerunner of this mobile drilling rig (MARUM-MeBo) already exists. It has been deployed on research ships in recent years for exploratory drilling in water depths down to 2000 metres, and can drill to around 100 metres into the sea floor. The second generation MeBo is now being built to drill up to 200 metres into the sediments. This rig will continue to be developed and tested in the ocean in the coming years. In the future methane hydrate reservoirs may be exploited using an ensemble of these small and, compared to large drilling platforms, relatively inexpensive bottom-deployed rigs. These de-vices have the advantage that they can be deployed to the ocean floor with any multi-purpose vessel or research ship. Expensive operations by drilling or special-purpose vessels would not be necessary.
Today, before a company begins to exploit a gas or oil reservoir, the extraction is generally simulated by computer. Sophisticated simulation programs are already available for gas and oil, calculating how pressure in a reservoir changes over periods of five to ten years and how this can reduce the production rate through time. These well-established simulation programs, among other parameters, take into account the geometry and temperatures of the reservoirs. A research institute is presently working on a software version that will also be able to simulate methane hydrate production. The software has yet to be fed with real measurement data from the ocean and laboratory. These would include information about the formation and dissociation rates of hydrates. In about two years the software should be ready to be put into use. One of the program’s strengths is that it can also simulate small reservoirs of around one square kilometre in detail, so it is capable of high spatial resolution.
fig. 3.10 > The underwater rig MARUM-MeBo has been used for several years for drilling on the sea floor. It is flexible in that it can be deployed from different research vessels. Methane hydrate could be mined in the future using similar equipment. © graphic design: A. Dibiasi für MARUM – Zentrum für Marine Umweltwissenschaften, Universität Bremen; photo: V. Diekamp, MARUM – Zentrum für Marine Umweltwissenschaften, Universität Bremen