The present invention relates to a system and a method for oil and/or gas development, and more specifically the invention relates to an apparatus and a method as stated in the preamble of claims 1 and 6, respectively.

State of Art for the development of oil and gas fields near to shore is characterized by the use of long reach wells being drilled from the shore to the reservoir. Examples of such developments are BP's Wytch Farm development in southern England and the near shore part of Exxon's Sakhalin I development. In both cases the wells are drilled to an approximate distance of 15 km from the shore. These projects represent state of art with respect to long reach drilling from shore. In case of suitable rock properties, where the borehole can be kept open, it is expected that the reach can be extended to 20 km and possibly to 25 km from shore in a not too distant future.

For several projects (for example for the Troll project offshore Norway in the late 1970's) it has been suggested to use tunnels from shore to get in position vertically or near vertically above the oil or gas reservoir whereby drilling and production would be undertaken in large mountain halls where personnel, according to the inventors, could work in safe manner with sufficient ventilation. The tunnel concepts have generally incorporated parallel tunnels; a work and operation tunnel in parallel with an escape tunnel. Safety concerns have, however, been raised as only a small leakage of gas or hydrogen sulfide would endanger the personnel. Most operators have, therefore, abandoned the idea of oil and gas mining in this mode. Others, however, are exploring the option of specially designed escape tunnels and extensive use of safety barriers to safeguard personnel in connection with further development of the tunnel ideas.

An object of the present invention is to avoid or mitigate the above and/or other problems or deficiencies, by providing a system and a method as stated in the characterizing clause of claims 1 and 6, respectively.

Advantageous embodiments of the invention are stated in the dependent claims.

A concept of the invention, incorporating the establishment of a tunnel from shoreline, is thus intended to be used for the development of near shore oil and gas fields out of distance of the reach of traditional drilling techniques and the concept is intended for safe and efficient drilling and development of such fields. The concept could also be applied from an artificial island being placed at an appropriate location in the sea.

According to the above concept or system, personnel are completely prohibited from working in enclosed areas where hydrocarbons could be present.

The background for the present invention is the following:

• It is known that very long tunnels can be prepared at reasonable costs in competent soils and rocks. Even rocks with poorer qualities can be penetrated by tunnels provided these tunnels are strengthened, for example by concrete linings. The tunnel under the Channel from France to Britain was, for example, drilled partly through very poor quality chalk, which after strengthening has proven to be a successful tunnel.

• It is, furthermore, known that oil and gas exploration and production can take place in deep waters where the temperature is low and the pressure is very high. Pressures up to an equivalent water depth of 3000 m or more can be handled by exploration equipment and pressures up to 2000 m can be handled by stae of art production equipment. The equipment can be mounted by specialized vessels working on dynamic position. In some instances the equipment is lowered to the sea floor on cables mounted between the seafloor and the rig/the vessel, these are so called "wire-line operations".

The present invention could be used to provide reach from the shore to a distance equal to the required length of the tunnel (say 30 km) plus 15 km (in a long reach deviation drilling mode). As such, oil and gas fields 15 to 45 km from shoreline (and potentially even much longer) could be reached safely by the present invention. A limitation exists in the case the sea bottom is much deeper than the depth where tunnels can be drilled or excavated. This might be the case for some locations offshore Norway where the water depth increases very fast from the shoreline.

The following expected advantages should in particular be noted:

• The tunnel concept or system allows for reaching oil and gas fields from shore to a distance of, say 45 km or more • The tunnel concept or system allows for environmentally safe operations where there are no contacts with the offshore environment

• The tunnel concept or system allows for safe operations with the use of remote equipment without exposing personnel to any danger of working in an enclosed environment where hydrocarbon gases could be present (as has been suggested by those promoting the use of tunnels where personnel will be working in an atmosphere that may contain hydrocarbons).

• The heavy equipment needed can safely be handled by remote operational vehicles that easily can handle submerged equipment that can be designed to have a weight that is suitable for handling by such vehicles.

• In order to represent an economic solution, a number of wells (typically, from 8 to 12 or even more) should be drilled from each technology tunnel. The number to be depending on the capacity/area of the end of the tunnel.

In the light of the present disclosure it follows that traditional sub sea equipment can be employed under atmospheric or pressurized conditions in a long tunnel. A tunnel consept or system according to the present invention and combining the above solutions is then described below, by referring to the enclosed drawings in which:

Figure 1 is a longitudinal section view of a tunnel concept or system according to the present invention,

Figure 2 is a cross section along the line A-A in fig. 1, and

Figure 3 is a cross section along the line B-B in fig. 1.

As shown in fig. 1 , a tunnel 1 is drilled or excavated by some conventional drilling or excavation equipment below the seafloor 3 from a shore location 2 to a pre-determined depth 4 below the sea level 5 and having a predetermined length. The depth could for example be 300 meters and the length 30 km. In this respect it should be noted that the Lasrdal road tunnel in Norway is the world's longest of its kind, 24 510 m. The new Gottard tunnel to be opened in Switzerland in 2010 will be 57 072 m. The deepest tunnel is the Norwegian Eiksund tunnel down to 287 m below sea level. The tunnel should have an overburden of, say, about 100 m of rock, depending on the strength of the overburden rock.

When drilling from shore into areas where hydrocarbons could be present, there is a danger of drilling into shallow gas pockets. Safeguarding to detect potential gas pockets involves shallow seismic surveys, use of probe holes that are drilled in front of the drilling machine and a drilling head that can stop gas under pressure. The danger of hitting shallow gas pockets will be less in case the tunnels are drilled closer to the sea floor.

The tunnel 1 described above is to be regarded as a technology tunnel and could house drilling equipment 9 and production equipment 6 such as separators, etc. that will be mounted at a distal end 7 of the tunnel where the tunnel 1 can be widened into larger mountain halls (not shown). During the preparation work of the tunnel 1, full access can be granted.

As shown in more details in figs. 2 and 3, equipment 9 for drilling exploration or production wells remotely can be mounted at the end 7 of the tunnel 1, and during all drilling and operations the tunnel 1 should be kept free from human access. Drill pipes and casing pipes (not shown) would be fed to a drilling rig (not shown) on a rail system, of which rail system rails 8 are shown. All access to the equipment 6, 9 can be "wire line" or on the rails 8 whereby full control of the work can be maintained. A cross section 10 of the tunnel 1 should be sufficient to ensure that all equipment can be transported through the tunnel 1 and there should in addition be space for electric cables 11 to drive the drilling process, for an umbilical 12 to secure hydraulic steering of the drilling process and for return pipes 13 to move the drilling mud to the opening for cleaning and return, for pipes 14 to allow for the well stream to be transported to the shoreline and any other equipment as deemed necessary. There are underway developments to prepare remote drilling from a rig mounted at the seafloor, the so- called "sea bed rig" project, and it is assumed that remote drilling in a tunnel can capitalize on the technology developments being undertaken in connection with the "sea bed rig".

In particular there should be room for remote operated vehicles to enter the technology tunnel 1 to assist during the drilling and the production and to carry out maintenance work. These could run on the rails 8 and finally, be manipulated to move on a combination of a rail system and a jacking system (not shown). Alternatively, the lower, distal end 7 of the tunnel 1 can be water filled to allow Remote Operated Vehicles (ROVs) to operate in a traditional sub sea mode, however, under a few bar pressure.

In a production mode, the well-heads 21 are placed at the end 7 of the tunnel and connected with pipes 22 to a manifold 23 for transfer of the well fluid to shore through the well stream pipe 14. The equipment 21-23 shall be designed for easy change out by ROV in accordance with State-of-the-Art for sub sea equipment. It should be noted that remote operations in a sub sea mode are considerably simplified as compared to a dry mode as all equipment can be made with a "submerged weight" that is suitable for handling with the ROVs.

In case of need for heavy repair of the technology tunnel 1 or equipment 6, 9, all operations should stop, the tunnel 1 could be emptied and repair undertaken. This could be done by personnel entering the tunnel as there is no hydrocarbon related activities ongoing.

At a certain distance from the shoreline, the tunnel 1 can be expanded into several branches (not shown) from which wells can be drilled and production equipment 9 can be installed. A tunnel for the purpose of hydrocarbon exploration can be expanded into more branches after the first exploration well has been drilled following the proper sealing of the exploration well.

As sub sea equipment is developed to work under a pressure of 200 bars and 2000 m from a vessel (or even at considerably deeper depth), it should be reasonable to assume that such equipment could be capable of working under the pressure of a few bars (note that 1 bar represent the pressure of 10 meters of water head), however, at a very long distance from the shoreline.

The present invention is not restricted to the embodiment described above, but can be varied within the scope of the enclosed claims.