System and methodology for running casing strings through a conductor tube

Abstract

A technique facilitates miming of casing strings in a multilateral well. A conductor tube may be placed into a hole formed in a seabed. A plurality of oriented casings is deployed in the conductor tube and the oriented casings have a specific exit angle and azimuthal orientation. The orientation of each oriented casing is used to direct a corresponding drilling of a borehole and placement of a casing in the borehole in a manner which does not interfere with other boreholes and casings.

What is claimed is: 
     
         1 . A method for orienting casing strings, comprising:
 drilling a hole in a seabed;   positioning a conductor tube into the hole;   arranging a plurality of oriented casings in the conductor tube via modules which are aligned to position the oriented casings so as to extend in a desired orientation;   operating a drill string through each orienting casing to form a borehole extending beneath the conductor tube along the desired orientation; and   placing casing along each borehole.   
     
     
         2 . The method as recited in  claim 1 , further comprising performing a cementing operation through an oriented casing of the plurality of oriented casings in the conductor tube prior to forming the boreholes beneath the conductor tube. 
     
     
         3 . The method as recited in  claim 2 , wherein cementing comprises pumping cement down one oriented casing of the plurality of oriented casings. 
     
     
         4 . The method as recited in  claim 3 , further comprising providing a check valve in each oriented casing to block upflow of cement into the plurality of oriented casings during cementing. 
     
     
         5 . The method as recited in  claim 1 , wherein deploying the plurality of oriented casings comprises deploying two oriented casings in the conductor tube. 
     
     
         6 . The method as recited in  claim 1 , wherein deploying the two oriented casings comprises deploying the two oriented casings so as to extend into the conductor tube from a dual wellhead. 
     
     
         7 . The method as recited in  claim 1 , wherein deploying the two oriented casings comprises deploying the two oriented casings so as to extend into the conductor tube from a well bay. 
     
     
         8 . The method as recited in  claim 6 , further comprising locating a plurality of the dual wellheads on a platform; and using pairs of the oriented casings for each wellhead so as to provide unique orientations relative to the orientations of other pairs of oriented casings. 
     
     
         9 . The method as recited in  claim 1 , further comprising aligning the modules via alignment pins and corresponding alignment openings in adjacent modules. 
     
     
         10 . A system for orienting casing strings, comprising:
 a platform cooperating with a plurality of conductor tubes extending beneath a platform to a seabed location, each conductor tube having a plurality of oriented casings which are arranged to provide a desired exit angle and azimuthal orientation, the plurality of oriented casings in the plurality of conductor tubes being arranged to facilitate formation of boreholes extending from the pluralities of oriented casings; and   a plurality of borehole casings placed in the boreholes so each borehole casing extends from a corresponding oriented casing of the pluralities of oriented casings without interference from other boreholes or borehole casings.   
     
     
         11 . The system as recited in  claim 10 , wherein the plurality of oriented casings in each conductor tube comprises two oriented casings. 
     
     
         12 . The system as recited in  claim 10 , wherein the plurality of oriented casings in each conductor tube comprises check valves to facilitate cementing operations. 
     
     
         13 . The system as recited in  claim 10 , wherein the borehole casings are cemented in the corresponding boreholes. 
     
     
         14 . The system as recited in  claim 10 , wherein the plurality of oriented casings is constructed via an assembly of sequential, oriented modules. 
     
     
         15 . A method, comprising:
 placing a plurality of conductor tubes into a seabed in conjunction with a platform;   arranging a plurality of oriented casings in each conductor tube;   using the orientation of each oriented casing to direct a corresponding drilling of a borehole and placement of a borehole casing in the borehole without interfering with other boreholes and borehole casings associated with other oriented casings.   
     
     
         16 . The method as recited in  claim 15 , further comprising assembling the plurality of oriented casings as a series of modules arranged to establish the desired exit angle and azimuthal orientation for each plurality of oriented casings. 
     
     
         17 . The method as recited in  claim 15 , further comprising performing a cementing operation through at least one of the oriented casings. 
     
     
         18 . The method as recited in  claim 17 , further comprising placing check valves at lower ends of the oriented casings. 
     
     
         19 . The method as recited in  claim 15 , further comprising cementing each borehole casing in its corresponding borehole. 
     
     
         20 . The method as recited in  claim 16 , further comprising using alignment features to couple together a desired sequence of modules containing sections of the oriented casings.