Methods and apparatus for forming an offshore well

Abstract

A method for forming an offshore well comprises forming a well structure ( 1 ) which includes a lower well portion extending below a seabed and an upper well portion ( 2 ) extending upwardly between the seabed ( 18 ) and a terminating upper end ( 3 ) of the well structure, wherein the well structure comprises a plurality of concentrically arranged tubular strings ( 22 ) and at least one annulus ( 48 ) defined therebetween. The method includes steps for minimising the bending stiffness of the upper well portion. In one example minimising the bending stiffness of the upper well portion may comprise partially filling at least one annulus with cement ( 52 ) to a height which: is intermediate the seabed and the terminating upper end of the well structure. In another example minimising the bending stiffness of the upper well portion may comprise providing a cement disruptor within at least one annulus and locating cement within said at least one annulus to define a cement sheath, wherein the cement disruptor, for example sleeve ( 122 ), reduces resistance of at least a portion of the cement sheath to bending of the upper well portion. In a further example minimising the bending stiffness of the upper well portion may comprise locating a flexible material within at least one annulus; and In a further example minimising the bending stiffness of the upper well portion may comprise varying the bending stiffness along at least one of the plurality of tubular strings.

1 . A method for forming an offshore well, comprising:
 forming a well structure which includes a lower well portion extending below a seabed and an upper well portion extending between the seabed and a terminating upper end of the well structure, wherein the well structure comprises a first tubular string and a second tubular string located within the first tubular string with a first annulus defined therebetween;   partially filling the first annulus with cement to a first height which is intermediate the seabed and the terminating upper end of the well structure such that a region of the first annulus above the first height is substantially void of cement to minimize bending stiffness in the upper well portion;   forming at least a portion of the well structure with the terminating upper end thereof in one of a first position and a second position, and subsequently moving the terminating upper end of the well structure to the other of the first and second positions, wherein such movement induces bending of the upper well portion.   
     
     
         2 . (canceled) 
     
     
         3 . The method of  claim 1 , wherein the upper well portion extends above a surface of the sea with the terminating upper end of the well structure aligned with a surface platform. 
     
     
         4 . The method of  claim 1 , wherein the first tubular string comprises a conductor pipe, and the method comprises inserting the conductor pipe into the seabed such that a portion of the conductor pipe extends upwardly from the seabed to the terminating upper end of the well structure, and the second tubular string comprises a casing string, and the method comprises inserting the casing string within the conductor pipe to define the first annulus therebetween, wherein the casing string extends upwardly to the terminating upper end of the well structure. 
     
     
         5 . (canceled) 
     
     
         6 . The method of  claim 1 , wherein the first tubular string comprises a first casing string and the second tubular string comprises a second casing string located within the first casing string. 
     
     
         7 - 9 . (canceled) 
     
     
         10 . The method of  claim 1 , wherein a tubular string support or guide arrangement is provided between the first and second tubular strings to provide load transference and/or guiding between the first and second tubular strings, at least prior to locating cement within the first annulus, wherein the method comprises embedding the tubular string support or guide arrangement within the cement. 
     
     
         11 - 12 . (canceled) 
     
     
         13 . The method of  claim 1 , a comprising performing a subsequent cementing operation following movement of the terminating upper end of the well structure to add cement into the first annulus to a second height. 
     
     
         14 . The method of  claim 1 , comprising placing a flexible material within the first annulus above the first height of the cement. 
     
     
         15 - 16 . (canceled) 
     
     
         17 . The method  claim 1 , comprising installing a third tubular string as part of the well structure, wherein a second annulus is defined between the third tubular string and one of the first and second tubular strings. 
     
     
         18 . (canceled) 
     
     
         19 . The method of  claim 17 , comprising partially filling the second annulus with cement. 
     
     
         20 . The method of  claim 17 , comprising providing fluid communication between the first and second annuli above the first height, wherein fluid communication is provided via a valve. 
     
     
         21 . The method of  claim 20 , comprising circulating a fluid between the first and second annuli. 
     
     
         22 . (canceled) 
     
     
         23 . The method of  claim 1 , wherein the terminating upper end of the well structure is configured to be moved between the first and second positions by a moving mechanism connectable between the first tubular string and a wellhead platform,
 and wherein the first tubular string is configured to be laterally constrained by a guide, the guide being connected to the wellhead platform by a rigid guide system,   the first height being arranged to allow bending of the well structure at or above the guide on actuation of the moving mechanism.   
     
     
         24 . The method of  claim 23 , wherein the first height is one of:
 substantially level with the guide; and above the guide.   
     
     
         25 . The method of  claim 24 , wherein the first height is above the guide by a distance of up to 5 metres. 
     
     
         26 . (canceled) 
     
     
         27 . A method for forming an offshore well, comprising:
 forming a well structure which includes a lower well portion extending below a seabed and an upper well portion extending between the seabed and a terminating upper end of the well structure, wherein the well structure comprises a first tubular string and a second tubular string located within the first tubular string with a first annulus defined therebetween;   locating cement within the first annulus to define a cement sheath; and   providing a cement disruptor within the first annulus, wherein the cement disruptor reduces resistance of the cement sheath to bending of the upper well portion.   
     
     
         28 . The method of  claim 27 , wherein the cement disruptor provides a localised weakness at a location along the cement sheath and the method comprises bending the upper well portion to cause failure of the cement sheath at the location of the weakness. 
     
     
         29 - 30 . (canceled) 
     
     
         31 . The method of  claim 27 , wherein the cement disruptor provides a localised reduction in the thickness of the cement sheath. 
     
     
         32 . (canceled) 
     
     
         33 . The method of  claim 27 , wherein the cement disruptor comprises or defines one or more flow passages or channels to permit cement to flow past the cement disruptor during location of cement within the first annulus, and the method comprises embedding at least a portion of the cement disruptor in the cement. 
     
     
         34 . The method of  claim 27 , wherein the cement disruptor comprises a sleeve mounted on at least one of an inner surface of the first tubular string and an outer surface of the second tubular string. 
     
     
         35 . (canceled) 
     
     
         36 . The method of  claim 27 , wherein the cement disruptor comprises one or more protuberances which extend into the first annulus, wherein the one or more protuberances extend from one or both of the first and second tubular strings. 
     
     
         37 . The method of  claim 27 , wherein the cement disruptor comprises a coating applied to one or both of the inner surface of the first tubular string and outer surface of the second tubular string, wherein the coating disrupts adherence of the cement sheath to one or both of the first and second tubular string. 
     
     
         38 - 42 . (canceled) 
     
     
         43 . The method of  claim 27 , wherein the terminating upper end of the well structure is configured to be moved between first and second positions by a moving mechanism connectable between the first tubular string and a wellhead platform,
 and wherein the first tubular string is configured to be laterally constrained by a guide, the guide being connected to the wellhead platform by a rigid guide system,   the method comprising locating the cement disruptor at a location arranged to allow bending of the well structure at or above the guide on actuation of the moving mechanism.   
     
     
         44 . The method of  claim 43 , wherein the location of the cement disruptor is one of: substantially level with the guide; and above the guide. 
     
     
         45 - 47 . (canceled) 
     
     
         48 . An offshore well installation, comprising:
 a well structure which includes a lower well portion extending below a seabed and an upper well portion extending between the seabed and a terminating upper end of the well structure, wherein the well structure comprises a first tubular string and a second tubular string located within the first tubular string with a first annulus defined therebetween;   a cement sheath at least partially filling the first annulus; and   a cement disruptor located within the first annulus.   
     
     
         49 - 69 . (canceled) 
     
     
         70 . The method of  claim 1 , comprising performing operations to form the offshore well from a drilling rig comprising a drill center, wherein the first position is aligned with the drill center of the drilling rig.