A METHOD FOR ESTABLISHING A CONNECTION FROM THE SEA BED TO A TUNNEL POSITIONED BELOW

Abstract: A method for establishing a "full profile" connection between the sea bed (1) and a tunnel (3) or a part thereof located below the sea bed. The tunnel is blasted and/or drilled from the shore and the tunneling operation is carried out so near the sea bed surface as possible without exposing the crew and equipment for danger. The connection betweeen the sea bed and the tunnel is brought about by drilling from the sea bed (1) a number of holes (8) which end in the tunnel (3), the holes having a total through-flow cross section which in hydrodynamic respect at least corresponds to the cross section of the tunnel.

Description: A method for establishing a connection from the sea bed to a tunnel positioned below The present invention relates to a method for estab¬ lishing a connection from the sea bed to a tunnel which is provided in advance by blasting or drilling. Such tunnel connections are necessary in so called ocean 5. thermical energy plants producing energy by utilizing the temperature difference between the surface water and water on great depth. In contructing power plants of the conventional design it is e.g. usual practice to establish a connec- 10. tion between a sub-water-formation tunnel and a sea by blasting from the inside, which will say from the rear side, the last portion of the tunnel, which will say the front portion of the tunnel, and the blasted rock is taken up by a cave blasted out in the tunnel. The security of 15. this method decreases with the water depth and at a depth of several hundred meters the method is considered not sufficiently safe in performance, paricularly with re¬ gard to water leakage in the last part of the tunnelling operation. Therefore it is necessary to develop a method 20. wherein a conventional tunnelling operation can be finished at a safe distance from the sea bed surface of the rock formation. In connection with crude oil exploiting from the sea bed it is formerly known to finish a tunnel at a 25. distance from the sea bed surface and seal the front portion of the tunnel from the remaining part thereof and subsequently drill a hole from the inside of the tunnel through the remaining portion of the sea bed formation. A pipeline is then extended from the outside 30. through the drilled hole. The diameter of the pipeline is insignificant in relation to the diameter of the tunnel. The object of this invention is to provide a safe method of establishing a connection of the kind stated introductory, said connection having a flow cross, section, in hydraulic respect substantially correspon¬ ding to the cross section of the tunnel. The purpose of this invention is obtained by drilling from the sea 5. bed surface a plurality of drilling holes ending in the tunnel and having a total flow cross section which in hydrodynamic respect is corresponding at least to the cross section of the tunnel. To release the large pressure difference between the water side and the air 10v side, the tunnel is filled with water before establish¬ ing the through-flow-connection. The drilling operation is carried out preferably from a floating or semi- submergeable drilling vessel or the like and drilling templates are used to line. The 15. method according to the invention is applicable for vertical drilling as well as for inclined drilling. The invention solves the problems in a simple and safe manner in the previously known flow communication establishing methods. Instead of carrying out the 20. establishing operation from the inside, the operation by drilling is carried out from the outer side, which will say from the water side. In this way it has been obtained that the tunnelling operations can be finished at a sufficiently safe distance from the surface of the 25. rock formation. The invention shall be explained more closely in the following by means of examples and with reference to the drawings, wherein Fig. 1 is illustrating diagramatically a vertical 30. drilling operation for obtaining a tunnel connection in accordance with the invention, fig. 2 is illustrating inclined drilling, fig. 3 is illustrating mounting of the drilling line for a inclined drilling operation and fig. 4 is showing diagramatically a drilling template 35. with a guide funnel. Fig. 1 shows a vertical cross section formation 3 . 00073 with a cold water tunnel for an ocean thermal energy plant. For such an energy plant, e.g. of 5 MW, it can be suitable to provide a tunnel for receiving cold water 2 having a cross section of ca. 20 m . In the figure, 1 5. is the rock surface,.(sea bottom surface), 2 is the vertical portion of the rock tunnel and 3 is the hori¬ zontal portion of the tunnel. An alternative embodiment with a curved tunnel is shown at 4. The drilling opera¬ tion in connection with the tunnelling is carried out by 10. means of a drill ship or a semi submergeable drilling platform 5. The platform is anchored above the drilling place, e.g. by means of dynamic positioning. The start¬ ing of the hole drilling is performed preferably with the help of a steel template frame 6 adjusted in advance 15. and having centring means for the drilling string 7. The number of drilling holes 8 is determined by the necessary cross section. A cave for rock drilled out and blasting rock rest if any, is shown at 9. The normal maximum diameter in crude oil industry is at the present 20. 36", which will say that 25-30 holes are needed for a 2 cross section of 20 m . The hole length will depend on the geometry of the rock surface (sea bed) and the geography of the tunnel. By a suitable placing of the contact location the 25. drilling operation of the holes can be performed quickly, effectively and economically and above all safely. Fig. 2 is illustrating an alternative method. The drill holes 8 are drilled obliquely in order to obtain better flowing conditions at the inlet to the tunnel 3 30. or/and the cave or rock space 9, resp. It appears from the figure;.that the extension of the cave is relatively large in relation to the cross section of the tunnel. Thereby, a greater possibility is provided for a suit¬ able locating of a great number of drilling holes, and 35. thereby a better water supply and better hydraulic relations at the inlet to the tunnel. It also appears /NO85/00073 from the figure that the drilling template 6 is provided with a guide funnel 10 which is pivotably journaled at 11. The drilling string is extending along an arcuade path from the drilling vessel 5 to the guide funnel 10 5. of the template so that the lowest portion of the dril¬ ling string with the drilling head is registering (on line) with the intended drilling direction. The template can be made with as many guides as necessary for drilling holes in the sea bed, however, it can also be provided 10. with one or more guides which can be moved longitudinally and transversally on the drilling template frame. Such drilling templates are known from vertical drilling in a substantially horizontal sea bed. The guide funnel 10 may also be arranged for rotary movement so that ar.. 15. circular drilling hole design is obtained. Fig. 3 illustrates a method for adapting the drilling string for inclined drilling. The drilling template 6 is provided with a guide funnel 10 for accomodating the lowermost portion of the drilling string (see also fig. 20. 4) . In position I the drilling vessel is located straight above the guide funnel and the drilling head is guided into the funnel as a consequence of the weight of the drilling string. Subsequently, the drilling vessel is displaced to position II and at the same time new drilling 25. string sections are put into the string while the guide funnel 10 is provided to obtain a. correct drilling angle. An auxiliary vessel 12 helps to keep the drilling head in position when moving the drilling vessel. Fig. 4 shows diagramatically a drilling template 30. frame 6 shaped as a sledge (sled) for moving across a sea bed and provided with a pivotable guide funnel 10 as also shown in fig. 2.

Claims: C l a i s 1. A method for establishing a full profile connection between the sea bed and a tunnel or a part thereof positioned below the sea bed, particularly on great sea depth, wherein the tunnel is blasted and/or drilled 5. in the rock formation with the front portion thereof as near as possible the sea bed surface without exposing the personnel and equipment for danger, c h a r a c t e r i z e d i n that the connection is brought about by drilling from the sea bed surface 10. a number of drilling holes ending in the tunnel and which have a total through flow cross section which in hydrodynamic respect corresponds to at least the cross section of the tunnel. 15. 2. A method according to claim 1, c h a r a c t e r i z e d i n that the tunnel before establishing of contact is filled with water for equalization of pressure. 20. 3. A method according to claim 1 or 2, c h a r a c t e r i z e d i n that the front portion of the tunnel before the drilling operation is started is extended with a rock cave to receive the drill rock and blast rests and/or for suitable locating of the 25. drilling holes relatively to the tunnel. 4. A method according to claim 1 or 2, c h a r a c t e r i z e d i n that the drilling operation is carried out from a floating boring vessel 30. or the like using a drilling template which is adapted the sea bed so that the template guides under use extend substantially perpendicularly. 5. A method according to claim 1, 2 or 3, c h a r a c t e r i z e d i n that the drilling operation is carried out from a floating drilling vessel or the like using a drilling template which is adapted 5. the sea bed so that the template guides when in use substantially extend rectangularly onto the sea bed. 6. A method according to claim 5, c h a r a c t e r i z e d i n that the drilling template 10. with pivotable guide funnels or funnel is used. 7. A method according to claim 6, for drilling obliquely in inclining sea bed, c h a r a c t e r i z e d i n that the drilling 15. vessel or the like first is located straight above the guide funnel of the drilling template and the head portion of the drilling string is placed therein, whereupon the drilling vessel is moved to a new position as the drilling string is bended so that the drilling head portion 20. registers with the intended drilling direction as the guide funnel is turned correspondingly during the dis¬ placing operation.

Inventors: HALMRAST BJOERN, HALMRAST, BJOERN
Applicants: AMR ENG AS, SELMER AS ING F, AMR ENGINEERING A/S, INGENIOER F. SELMER A/S
Application year: 1985
Main classification: E21D10
IPC codes: E21B7, E21B43