Drilling system and method

Abstract

A system for drilling a subterranean bore at a subsea location is provided, the system comprising a drilling unit for location on the seabed and remotely operable from the water surface to drill a bore using a drill string; a transport assembly moveable between the water surface and the drilling unit when at the location on the seabed, wherein the transport assembly comprises a receptacle for receiving a downhole tool; first transfer means for transferring a first downhole tool from the drill string to the transport assembly; and second transfer means for transferring a second downhole from the transport assembly to the drill string; whereby the first and second transfer means are operable to recover from the drill string a first downhole tool and deliver to the drill string a second downhole tool in a single deployment of the transport assembly from the water surface to the drilling unit. A method for drilling a subterranean bore at a seabed location comprises providing a drilling unit on the seabed; conducting a drilling operation using a drill string by remote operation of the drilling unit from a surface location, the drill string having therein a first downhole tool; transporting a second downhole tool from the surface to the drilling unit by means of a transport assembly; recovering the first downhole from the drill string to the transport assembly; transferring the second downhole tool from the transport assembly to the drill string; transporting the first downhole tool to the surface by means of the transport assembly; and continuing the drilling operation using the second downhole tool. The system and method are especially useful in the recovery, transport and deployment of an inner tube for holding a core sample.

1 . A system for drilling a subterranean bore at a subsea location, the system comprising:
 a drilling unit for location on the seabed and remotely operable from the water surface to drill a bore using a drill string;   a transport assembly moveable between the water surface and the drilling unit when at the location on the seabed, wherein the transport assembly comprises a receptacle for receiving a downhole tool;   first transfer means for transferring a first downhole tool from the drill string to the transport assembly; and   second transfer means for transferring a second downhole tool from the transport assembly to the drill string;   whereby the first and second transfer means are operable to recover from the drill string the first downhole tool and deliver to the drill string the second downhole tool in a single deployment of the transport assembly from the water surface to the drilling unit.   
     
     
         2 . (canceled) 
     
     
         3 . The system according to  claim 1 , further comprising a guide assembly extending from the remote drilling unit, the transport assembly being provided with guide means for engaging with the guide assembly. 
     
     
         4 . (canceled) 
     
     
         5 . (canceled) 
     
     
         6 . The system according  claim 3 , wherein the guide means of the transport assembly comprises a plurality of guide members. 
     
     
         7 . The system according to  claim 6 , wherein the transport assembly comprises a first guide member at its upper end portion and a second guide member at its lower end portion. 
     
     
         8 . The system according to  claim 1 , wherein the receptacle of the transport assembly is arranged to hold both the first downhole tool and the second downhole tool. 
     
     
         9 . The system according to  claim 1 , wherein the receptacle comprises a housing within which one or more of the downhole tools may be retained. 
     
     
         10 . The system according to  claim 9 , wherein the housing comprises a main housing portion and a secondary housing portion each arranged to hold a respective downhole tool. 
     
     
         11 . (canceled) 
     
     
         12 . (canceled) 
     
     
         13 . The system according to  claim 1 , wherein the receptacle comprises a first portion for holding the first downhole tool and a second portion for holding the second downhole tool. 
     
     
         14 . The system according to  claim 13 , wherein the first portion being arranged to receive its downhole tool recovered from the drill string and the second portion is arranged to deliver its downhole tool to the drill string. 
     
     
         15 . The system according to  claim 14 , wherein the recovery of the downhole tool to the first portion triggers the release of the downhole tool from the second portion. 
     
     
         16 . The system according to  claim 1 , wherein the transport assembly comprises the first transfer means, the first transfer means being an overshot deployable from the transport assembly into the drill string to retrieve the respective downhole tool therefrom. 
     
     
         17 . (canceled) 
     
     
         18 . The system according to  claim 1 , wherein the transport assembly comprises the second transfer means. 
     
     
         19 . The system according to  claim 18 , wherein the second transfer means comprises a releasable retaining means for holding its downhole tool in the receptacle. 
     
     
         20 . The system according to  claim 18 , wherein the second transfer means is activated to release its downhole tool from the receptacle under the action of an elevated fluid pressure. 
     
     
         21 . The system according to  claim 1 , wherein the transport assembly is engageable with the drill string. 
     
     
         22 . The system according to  claim 21 , wherein the transport assembly is engageable with the upper end of the drill string. 
     
     
         23 . (canceled) 
     
     
         24 . A system for drilling a subterranean bore at a subsea location, the system comprising:
 a drilling unit for location on a seabed and remotely operable from the water surface to drill a bore using a pre-assembled drill string;   a transport assembly moveable between the water surface and the drilling unit when at the location on the seabed, wherein the transport assembly comprises a receptacle for receiving a downhole tool;   engaging means for releasably engaging the transport assembly with the upper end of the drill string; and transfer means for transferring a downhole tool between the transport assembly and the drill string.   
     
     
         25 . (canceled) 
     
     
         26 . (canceled) 
     
     
         27 . (canceled) 
     
     
         28 . A method for drilling a subterranean bore at a seabed location, the method comprising providing a drilling unit on the seabed;
 conducting a drilling operation using a drill string by remote operation of the drilling unit from a surface location, the drill string having therein a first downhole tool;   transporting a second downhole tool from the surface to the drilling unit by means of a transport assembly; recovering the first downhole from the drill string to the transport assembly;   transferring the second downhole tool from the transport assembly to the drill string;   transporting the first downhole tool to the surface by means of the transport assembly; and continuing the drilling operation using the second downhole tool.   
     
     
         29 . The method according to  claim 28 , wherein the first and second downhole tools are inner tubes for holding a core sample. 
     
     
         30 . The method according to  claim 29 , wherein the first inner tube contains a core sample and the second inner tube is empty. 
     
     
         31 . (canceled) 
     
     
         32 . (canceled) 
     
     
         33 . (canceled) 
     
     
         34 . (canceled)