The "Oil Mine" concept is based on methods which have been used for generations, and consists of using tunnels and caverns in a way which permits production and transport of oil and gas from underneath the sea floor. 'Compared to oil and gas production from platforms, the "Oil Mine" offers many environmental and operational benefits.

INTRODUCTION

The early phase of oil field development in the North Sea was based on a scale-up philosophy, using the experiences from platform installations in The Gulf of Mexico. Soon this proved to be insufficient. Larger water depths and more severe weather conditions forced the oil companies to develop new solutions, and rising costs followed, generally far exceeding the estimated. Today, a further step is initiated, when exploration moves further north to The Norwegian Sea, to still deeper water, icing problems and dark season. The oil companies are now looking for new concepts to make oil and gas production possible in these areas. When considering arctic and antarctic conditions, with icebergs floating around uncontrolled, making deep scours in bottom sediments, the "Oil Mine" can prove to be the only practical solution. This can also be the case in areas with heavy ship traffic. At first glance the "Oil Mine" may appear to be an entirely new concept. It is, however, based on methods which have been tried out for generations. The methods are well known from excavation of tunnels and caverns for mines, roads, railways, waterpower construction and oil storage. Examples are given in Table 1. The idea itself, to use tunnels for the development of oil fields, appeared as U.S. patents as early as 1941. Later it has been dealt–with-in the literature, and has considered both The North Sea, (Andrews, 1978), and The North American arctic regions (McCusker and Tarkoy, 1976). Al though the concept is based on well-known methods, it should not be concealed that many problems still have to be evaluated, and further studies and investigations are needed. In the following the subaqueous development and operation of oil and gas fields are explained and discussed in more detail.

THE "OIL MINE" SCHEME - LAY OUT AND CONSTRUCTION

In order to evaluate aspects related to technical feasibility, safety, environment, economy and construction time, an idealized case has been worked out. The scheme is applied to an off-shore area in The Norwegian Sea, Troms II, which has been pointed out as a potential oil field. In Fig. 1, lay-outs and sections of the "Oil Mine" are shown. Sufficient space is allotted for a comprehensive amount of process and utility functions.

Descending Tunnels and Low Level Service Station

Four tunnels will be driven from the shore, or an islet, down to the service station at the lowest level. The elevation of this deepest point of the tunnel system will be determined on the basis of topographical and geological conditions. These sloping tunnels, each with a cross sectional area of 25 m, and a gradient of 12,5 %, will be placed in the basement rock.

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