Telescopic guide pipe for offshore drilling

Abstract

The present invention relates to a guide device for an off-shore drilling installation comprising at least one drilling riser extending from a floating support to a said guide device at the sea bottom, said drilling being performable from said floating support via said drilling riser using a drill string fitted at its end with drilling tools. According to the invention, said telescopic guide device comprises a telescopic guide pipe comprising coaxial telescopic pipe elements about an axis, the smallest-diameter innermost telescopic pipe element being fitted at its end for breaking up the ground suitable for progressively burying said telescopic guide pipe in the ground so as to enable a drilling tool to be guided more deeply into the ground.

1 . A guide device for an off-shore drilling installation comprising at least one drilling riser extending from a floating support to said guide device on the sea bottom, said drilling being performable from said floating support using a drill string fitted at its end with drilling tools passing through said drilling riser and said guide device, said guide device being characterized in that it comprises a telescopic guide pipe comprising coaxial telescopic guide elements about an axis XX′ and of decreasing diameters, the elements being pre-assembled one in another in such a manner that said telescopic pipe elements are suitable for sliding in the direction of said axis XX′ one inside another, the smallest diameter, innermost telescopic pipe element being fitted at its end with breakup means for breaking up the ground suitable for enabling said telescopic guide pipe to be progressively buried in the ground by sliding said telescopic pipe elements outwards, thereby enabling a drilling tool at the end of said drill string to be guided more deeply in the ground.  
   
   
       2 . A guide device according to  claim 1 , characterized in that said smallest-diameter innermost pipe element presents a diameter substantially equal to the diameter of said drilling riser.  
   
   
       3 . A guide device according to  claim 1 , characterized in that said means for breaking up the ground are constituted by a multiply-perforated capsule enabling water or mud to be jetted into the ground by being injected under very high pressure.  
   
   
       4 . A guide device according to  claim 1 , characterized in that it has at least three coaxial telescopic pipe elements.  
   
   
       5 . A device according to  claim 4 , characterized in that each of said telescopic coaxial pipe elements presents a length of 50 m to 300 m, preferably of 100 m to 200 m, said deployed guide pipe presenting a length of 150 m to 600 m, and preferably of 200 m to 300 m.  
   
   
       6 . A guide device according to  claim 1 , characterized in that it comprises a said telescopic guide pipe suitable for use in an off-shore drilling installation, in which at least one drilling riser extends from a floating support to a said guide device at the sea bottom, said drilling riser deflecting progressively from a substantially vertical position at said floating support to a position that is substantially horizontal or tangential to the horizontal at the sea bottom, said drilling being performable from said floating support via said drilling riser and said guide device in such a manner that the borehole in the sea bottom is begun at a given angle of inclination relative to the horizontal that preferably lies in the range 5° to 60°, and more preferably in the range 25° to 45°, said guide device being characterized in that it comprises a said telescopic guide pipe in a buried position in which said telescopic guide pipe in the retraced position or the outer telescopic pipe element when said telescopic pipe is deployed, comprises in succession: 
 a front end resting substantially horizontally on the sea bottom;    a curved intermediate portion buried in the subsoil of the sea bottom with a large radius of curvatures, preferably a radius of curvature greater than 500 m; and    a rear portion that is substantially linear and buried in the subsoil of the sea bed at said given angle of inclination;    said telescopic guide pipe or said outer telescopic element co-operating with controlled burying means enabling said retracted telescopic guide pipe to be buried in the sea bottom while said retracted telescopic guide pipe is being towed along the sea bottom from its front end, starting from an initial position in which said retracted telescopic guide pipe rests entirely on the sea bottom in a substantially horizontal position, to a said buried position in the subsoil of the sea bottom.    
   
   
       7 . A guide device according to  claim 6 , characterized in that said retracted telescopic guide pipe presents a length of 100 m to 600 m, preferably of 250 m to 450 m, with a said given angle of inclination of the guide pipe lying in the range about 10° to 60°, and preferably in the range 25° to 45°.  
   
   
       8 . A guide device according to  claim 6 , characterized in that said front end is engaged in a baseplate including a load and resting on a front soleplate such that said baseplate maintains said front end substantially horizontally on the sea bottom while it is being towed.  
   
   
       9 . A guide device according to  claim 6 , characterized in that said controlled burying means comprise: 
 a front soleplate placed on the sea bottom and supporting said front end and secured thereto;    at least one intermediate soleplate supporting said curved intermediate portion and/or the rear portion and secured thereto, of surface area that is smaller than that of said front soleplate, preferably a plurality of said intermediate soleplates distributed along said intermediate portion and said rear portion of surface area that becomes smaller relative to said front soleplate on approaching said rear end; and    an anchor connected to said rear portion and suitable for becoming buried in the ground under the effect of said traction applied to said front end.    
   
   
       10 . A guide device according to  claim 6 , characterized in that said controlled burying means comprise at least one deflector secured to said outer telescopic pipe element of said telescopic guide pipe in said intermediate portion or said rear portion of said retracted telescopic guide pipe, comprising plane surfaces that are preferably symmetrical about a vertical axial plane of said guide pipe in the longitudinal direction when it is in a rectilinear horizontal position, and said plane and deflector surfaces being inclined relative to a horizontal axial plane of said guide pipe when it is in a horizontal position on the sea bottom, said deflector being inclined at an angle in such a manner as to cause said retracted telescopic guide pipe to become buried when it is towed from said substantially horizontal initial position to a said buried position in the sea bottom.  
   
   
       11 . A guide device according to  claim 10 , characterized in that it has a plurality of deflectors distributed along the outer telescopic pipe element of said telescopic guide pipe, said deflectors being inclined at respective angles that become smaller for said deflectors that are closer to said front end.  
   
   
       12 . A guide device according to  claim 1 , characterized in that said controlled burying means comprise: 
 secondary pipes for jetting fluid and secured to said telescopic guide pipe, extending parallel thereto along the underface thereof; and    said secondary pipes being of smaller diameter than said telescopic guide pipe and having perforations in their underfaces enabling a fluid to be expelled towards the sea bottom when said secondary pipes are fed by a said fluid under pressure.    
   
   
       13 . A guide device according to  claim 12 , characterized in that said secondary pipes are connected via their ends to the front and rear ends of said retracted telescopic guide pipe, communicating with said front and rear ends in such a manner as to make it possible to feed them using a single feed pipe connected to said front end of said guide piped.  
   
   
       14 . A device according to  claim 1 , characterized in that the guide device comprises: 
 a rigid outer top structure covering and holding rectilinear said retracted telescopic guide pipe when it is substantially horizontal and rests on the sea bottom;    said outer structure presenting a longitudinal central opening in its bottom face enabling said retracted telescopic guide pipe to become buried in the ground when it is towed;    at least one connection connecting at least the rear portion * 3   3 ) of the outer telescopic pipe element of the telescopic guide pipe to said outer structure in such a manner as to prevent it from becoming buried beyond a given depth so as to limit the radius of curvature of said curved portion;    said outer top structure resting on the ground of the sea bottom, preferably via lateral soleplates situated on either said longitudinal central opening, said lateral soleplates preventing said rigid outer structure from becoming buried; and    said outer structure being secured to said baseplate in which said front portion of the guide pipe is engaged.    
   
   
       15 . A guide device according to  claim 14 , characterized in that it has a plurality of flexible connections distributed along the outer telescopic pipe element of said telescopic guide pipe and presenting lengths that become longer for connections that are closer to the rear end of the guide pipe and of lengths that are such that said guide pipe presents a said curved portion having a desired radius of curvature and a said rear portion that is linear.  
   
   
       16 . A method of making a guide device according to  claim 6 , characterized in that the following steps are performed: 
 placing a said telescopic guide pipe in the retracted position in a said initial position where it rests substantially horizontally and in rectilinear manner on the sea bottom, said telescopic guide pipe co-operating with said controlled burying means; and    towing the front end of said telescopic guide pipe in the retracted position along the sea bottom, preferably in the axial longitudinal direction of said guide pipe, from said initial position to a said buried position.    
   
   
       17 . A method of making a guide device according to  claim 16 , characterized in that guide devices according to  claim 8  or  claim 9  are used and the front end of said retracted telescopic guide pipe is towed until said intermediate soleplates are buried in the ground at increasing depth on coming closer to the rear end of the guide pipe so as to obtain the desired radius of curvature, preferably greater than 500 m, and more preferably lying in the range 500 m to 1000 m.  
   
   
       18 . A method of making a guide device according to  claim 16 , characterized in that a guide device according to  claim 10  or  claim 11  is used and the front end of said retracted telescopic guide pipe is towed until said deflectors are buried in the ground in a horizontal position so as to obtain a said desired radius of curvature preferably greater than 500 m, and more preferably lying in the range 500 m to 1000 m.  
   
   
       19 . A method of making a guide device according to  claim 16 , characterized in that a guide device is used according to  claim 12  or  claim 13 , and: 
 injecting gas under pressure into said secondary pipes when it is desired to tow said guide pipe on the sea bottom; and    injecting a liquid under pressure, preferably water, into said secondary pipes and preferably into said telescopic guide pipes closed at both ends and communicating with said ends of said secondary pipes when it is desired to bury said guide pipe.    
   
   
       20 . A method of making a guide device according to  claim 16 , characterized in that a guide device is used according to  claim 14  or  claim 15 , and the front end of said retracted telescopic guide pipe and said rigid outer structure secured to said guide pipe are towed until said connection(s) prevent at least said rear portion of said retracted telescopic guide pipe from becoming buried deeper so as to obtain the desired radius of curvature preferably greater than 500 m, and more preferably lying in the range 500 m to 1000 m.  
   
   
       21 . An off-shore drilling installation comprising a drilling riser extending from a floating support to a said guide device according to  claim 1 , to which said drilling riser is connected.  
   
   
       22 . An off-shore drilling installation according to  claim 21 , comprising a drilling riser extending from a floating support to a guide device according to any one of  claims 6  to  5 , to which said drilling riser is connected, said drilling riser deflecting progressively from a substantially vertical position at said floating support to a position that is substantially horizontal or tangential to the horizontal at the sea bottom, drilling being performable from said floating support via said drilling riser and said guide device in such a manner that a borehole begins in the sea bottom at a given angle of inclination relative to the horizontal, preferably lying in the range 10° to 80°.  
   
   
       23 . A method of making a drilling installation according to  claim 21 , characterized in that the following steps are performed: 
 making a guide device according to a method according to any one of  claims 16  to  20 ; and    connecting at least one said drilling riser to said front end of the guide pipe resting on the sea bottom.    
   
   
       24 . A method of drilling using a drilling installation according to  claim 21 , characterized in that drilling operations are performed and a borehole is constructed by deploying drill strings co-operating with drilling tools and columns of tubing via a said drilling riser and a said guide device buried in the sea bottom.