Keywords: underwater drilling rig, composites, oil, natural gas, Pro-Engineer, finite elements, ANSYS.

The paper presents a study on how to retrieve some of the 10 000 billion tonnes of deep sea methane hydrates that lie in the world's oceans, some 2 to 7.16 miles (3.22 to 11.52 km) underwater. The main part of the paper presents a conceptual design of an underwater drilling rig; which will not require legs of some 7.16 miles (11.52km) in length, if a conventional drilling rig were used. Although the main purpose of the rig is intended to retrieve deep sea methane that is found as a hydrate at the bottom of the oceans, the rig can also be adapted to retrieve deep sea oil. The current world shortage of oil and gas and the ever increasing demand for fossil fuels in the deep sea; such as that going on in the Gulf of Mexico at present, have prompted the work described in this paper. The recent 'blow-out' that occurred in the Gulf of Mexico is unlikely to occur with the present design as the rig will be wholly submerged in water. The design of this rig is aided by using CAD and CAE software; such as Pro-Engineer and ANSYS, for the first time. Moreover the use of these computer packages has shown that the buoyancy, hydrostatic stability and strength of the rig are satisfactory, providing that the rig is manufactured using a composite material. Considerations were also made on the health and safety of the crew, together with other important factors.

As the water depths involved in extracting oil and methane become deeper and deeper, it is only a matter of time that other technologies will be considered to achieve the job of extracting fuels. One of these fuels; which is plentiful, is methane; which as a fossil fuel is cleaner than oil and coal. Recently, Dickens et al. [1] discovered some 10,000 billion tonnes of this fuel lying some 2 to 7.16 miles (3.22 to 11.52 km) underwater. According to Ross [2], if this methane is distributed equally to all mankind then each and every one of us will get a 'chunk' of methane of mass of about 1,670 tonnes; the value of this methane will be about $1.25 million for each person on earth! Some people say "we should leave this methane where it is", but the present authors believe that with some emerging countries growing at about 8% per annum; humankind will resort to retrieving and using this methane. Moreover, with the continuing growth in the petroleum industry, this fuel could be an answer to a lot of the industry's problems in the future. In order to recover this fuel, the present authors believe that conventional drilling rigs will have reached their ability to tackle these great water depths and the solution will lie in using underwater drilling rigs, Ross and Laffoley-Lane [3].

In order to succeed, such task equipment volume requirements were calculated to give an approximate idea of the size of the structure. Knowing the size of the structure and having studied previous concepts [3], the design process was commenced by using powerful CAD and CAE design software, in the form of Pro-Engineer and ANSYS. Complete analysis was performed involving finite element analysis, once the final design of the rig was achieved. The strength and buoyancy calculations showed that the rig had to be constructed using a composite material; whose strength to weight ratio was much greater than that of high-tensile steel.

1

G.R. Dickens, C.K. Paull, P. Wallace, The ODP Leg 164 Scientific Party, "Direct measurement of in situ quantities in a large gas hydrate reservoir", Nature, 385, 426-428, 1997. doi:10.1038/385426a0

2

C.T.F. Ross, "Exploiting the deep oceans for energy retrieval and for the burial of carbon dioxide", The Open Oceanography Journal, 3, 50-58, Bentham Open Press, 2009.

3

C.T.F. Ross, G. Laffoley-Lane, "A Conceptual Design of an Underwater Drilling Rig", SNAME J of Marine Technology, 35(2), 99-113, April 1998.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £130 +P&P)