Removal of platforms at sea

Abstract

The present invention relates tot a method of removing an upper part of a platform which rests on a seabed and which extends above the waterline, the platform comprising legs which extend upwards from the seabed, the method comprising the subsequent steps of: providing a vessel comprising a single hull, the hull defining a contour of the vessel when viewed from above; providing a support structure which is configured to rest on the vessel, the support structure comprising one or more beams, the one or more beams having connection ends that are constructed to extend outside the contour of the hull on opposite sides of the vessel, the connection ends configured to be connected to the legs of the platform; positioning the vessel between the legs of the platform; connecting the connection ends to the legs of the platform; disconnecting the upper part of the platform from the lower part; lifting the upper part of the platform from the lower part by the vessel via the support structure; moving the vessel and the upper part of the platform away from the lower part of the platform. The present invention further relates to a system for carrying out the method.

1 . A method of removing an upper part of a platform which rests on a seabed and which extends above the waterline, the platform comprising legs which extend upwards from the seabed, the method comprising the subsequent steps of:
 providing a vessel comprising a single hull, the hull defining a contour of the vessel when viewed from above;   providing a support structure which is configured to rest on the vessel, the support structure comprising one or more beams, the one or more beams having connection ends that are constructed to extend outside the contour of the hull on opposite sides of the vessel, the connection ends configured to be connected to the legs of the platform;   positioning the vessel between the legs of the platform;   connecting the connection ends to the legs of the platform;   disconnecting the upper part of the platform from the lower part;   lifting the upper part of the platform from the lower part by the vessel via the support structure; and   moving the vessel and the upper part of the platform away from the lower part of the platform.   
     
     
         2 . The method of  claim 1 , the vessel further comprising a ballast system for varying the draft of the vessel, the method comprising:
 ballasting the vessel to a deep draft when positioned between the legs of the vessel; and   lifting the upper part of the platform by deballasting the vessel.   
     
     
         3 . The method of  claim 1 , wherein the support structure comprises a hydraulic system for raising the one or more beams including the platform relative to the vessel, the method comprising raising the upper part of the platform relative to the vessel by the hydraulic system, optionally while at the same time deballasting the vessel. 
     
     
         4 . The method of  claim 1 , comprising pre-assembling the support structure prior to the removal operation in order to fit the support structure to the size and shape of the platform which is to be removed. 
     
     
         5 . The method of  claim 1 , comprising:
 positioning the one or more beams of the support structure in a target position wherein the connection ends engage the legs;   supporting the one or more beams in their target positions by the platform via provisional or preliminary support means on the platform such that possible motions of the support vessel under influence of waves and wind do not affect or disturb the connecting of the one or more beams to the legs; and   connecting the one ore more beams to the legs.   
     
     
         6 . The method of  claim 1 , comprising:
 positioning the one or more beams of the support structure in a target position wherein the connection ends engage the legs;   supporting the one or more beams in their target positions by the platform via provisional or preliminary support means on the platform;   disconnecting the support structure from the vessel such that possible motions of the support vessel under influence of waves and wind do not affect or disturb the connecting of the one or more beams to the legs;   connecting the one ore more beams to the legs; and   reconnecting the support structure to the vessel prior to the lifting of the upper part of the platform from the lower part of the platform.   
     
     
         7 . The method of  claim 1 , wherein the beams are releasably arranged on the vessel such that the upper part of the platform and the support structure connected to it can be unloaded from the vessel by moving the beams relative to the vessel, the method comprising:
 moving the combination of the vessel and the upper part of the platform to a target location, and   unloading the upper part of the platform from the vessel by moving the beams and the upper part away from the vessel.   
     
     
         8 . The method of  claim 1 , comprising unloading the upper part of the platform from the vessel by moving the one or more beams including the upper part of the support structure substantially horizontally relative to the vessel. 
     
     
         9 . The method of  claim 3 , wherein the support structure comprises one or more rails or skid tracks which rest on the vessel, wherein the beams of the support structure are movably arranged on the one or more rails or skid tracks via wheels or skid means, the method comprising rolling or skidding the one or more beams relative to the vessel for unloading the upper part of the platform from the vessel. 
     
     
         10 . The method of  claim 1 , comprising removing the upper part of the platform from the vessel by
 positioning one or more support carriages on the deck of the vessel;   disconnecting the one or more beams from either the vessel deck or the platform;   lifting the upper part of the platform optionally including one or more beams from the deck; and   unloading the combination of support carriage, beams and upper part of the platform from the vessel.   
     
     
         11 . The method of  claim 1 , comprising unloading the upper part of the platform by moving the support structure and the upper part of the platform in a longitudinal direction of the vessel. 
     
     
         12 . The method of  claim 1 , comprising unloading the upper part of the platform by moving the upper part of the platform in a transversal direction of the vessel. 
     
     
         13 . The method of  claim 1 , comprising unloading the upper part of the platform by providing a docking station comprising a bay for the vessel and supports member positioned around the bay, the support members being configured to support the support beams of the support structure, the method comprising:
 positioning the vessel with the upper part of the platform in the docking station;   ballasting the vessel such that the vessel moves downward and the support beams engage the support members, thereby shifting the weight of the upper part of the platform from the vessel to the docking station; and   removing the vessel from the docking station.   
     
     
         14 . A system for removing an upper part of a platform which rests on a seabed and which extends above the waterline, the platform comprising legs which extend upwards from the seabed, the system comprising:
 a vessel comprising a single hull, the hull defining a contour of the vessel when viewed from above; and   a support structure which rests on the vessel, the support structure comprising one or more beams, the one or more beams having connection ends that extend outside the contour of the hull on opposite sides of the vessel, the connection ends configured to be connected to the legs of the platform.   
     
     
         15 . The system of  claim 14 , the vessel further comprising a ballast system for varying the draft of the vessel. 
     
     
         16 . The system of  claim 14 , wherein the one or more beams are movable in a substantially horizontal direction relative to the vessel. 
     
     
         17 . The system of  claim 14 , wherein the support structure comprises a hydraulic system which rests on the vessel and is configured to raise the one or more beams including the platform relative to the vessel. 
     
     
         18 . The system of  claim 14 , wherein the support structure comprises one or more beams having connection ends which project substantially horizontally away from the vessel, a central part of the beam resting on the vessel, such that the connection ends meet the legs of the platform for connection with the legs when the vessel is positioned between the legs of the upper part for the platform. 
     
     
         19 . The system of  claim 14 , wherein the connection ends of the support structure extend on opposite sides of the vessel, one end of a first beam being configured to be connected to a first leg of the platform, and the opposite end of the first beam being configured to be connected to a second leg of the platform. 
     
     
         20 . The system of  claim 14 , wherein the one or more beams are releasably arranged on the vessel such that the one or more beams are unloadable at a target location from the vessel together with the upper part of the platform. 
     
     
         21 . The system of  claim 14 , wherein the support structure comprises one or more rails or skid tracks which rest on the vessel, wherein the beams of the support structure are movably arranged on the one or more rails or skid tracks via wheels or skid means, such that the one or more beams may be rolled or skidded in a substantially horizontal direction relative to the vessel for unloading the one or more beams and the upper part of the platform from the vessel. 
     
     
         22 . The system of  claim 14 , wherein the support structure comprises one or more support carriages which rest on the deck of the vessel, the support carriages configured to carry the beams including the upper part of the platform, the support carriages further configured to move substantially horizontally relative to the deck for unloading the upper part of the platform from the vessel. 
     
     
         23 . The system of  claim 14 , wherein the support structure comprises one or more rails or skid tracks which rest on the vessel, and wherein the rails or skid tracks extend in a longitudinal direction of the vessel. 
     
     
         24 . The system of  claim 14 , further comprising provisional or preliminary support means constructed to support the one or more support beams in a target position on the platform such that possible motions of the support vessel under influence of waves and wind do not affect or disturb the connecting of the one or more beams to the legs. 
     
     
         25 . A support structure for use in the method of  claim 1 . 
     
     
         26 . A support structure for use in the system of  claim 14 . 
     
     
         27 . A vessel for use in the method of  claim 1 . 
     
     
         28 . A vessel for use in the system of  claim 13 . 
     
     
         29 . A docking station for unloading the platform from the vessel, the docking station comprising a bay for the vessel and support members positioned around the bay, the support members being configured to support the support beams of the support structure, thereby allowing the unloading method of:
 positioning the vessel with the upper part of the platform in the docking station,   ballasting the vessel such that the vessel moves downward and the support beams engage the support members, thereby shifting the weight of the upper part of the platform from the vessel to the docking station via the one or more support beams; and   removing the vessel from the docking station.