Method of forming a bore

Abstract

A method of forming a supported subterranean well bore in which, in one disclosed embodiment, a first drill bit is mounted on a first string of casing tubulars via a steerable tool, and the drill bit is used to form a first bore. Upon reaching the required depth the casing string is cemented in place to support the formed bore and a second drill bit is mounted on a second casing string and is inserted into the first casing string. The second drill bit is used to drill through the wall of the first casing string and proceed to form a second, deeper bore. Once the second drill bit has reached the required depth, the second casing string is cemented in place to support the second bore.

1 . A method of forming a supported bore comprising the steps of:
 locating a first drill bit on a first expandable tubular member;   drilling a first bore to a first depth;   expanding a portion of the first expandable tubular member to a larger diameter;   inserting a second drill bit mounted on a second tubular member within the first tubular member;   drilling through a wall portion of the first tubular member and drilling a second bore to a second depth.   
     
     
         2 . The method of  claim 1  further comprising locating the first drill bit on a steerable tool and mounting the steerable tool and first drill bit on the first expandable tubular member. 
     
     
         3 . The method of  claim 1  wherein said first expandable tubular member includes a deflecting member. 
     
     
         4 . The method of  claim 1  wherein said first expandable tubular member includes a means for determining at least one parameter of the bore. 
     
     
         5 . The method of  claim 1  wherein said first expandable tubular member includes a means for determining the orientation of the drill bit. 
     
     
         6 . The method of  claim 3  wherein the wall portion of the first tubular member is drilled through at the location of the deflecting member. 
     
     
         7 . The method of  claim 1  further comprising pumping cement into an annulus formed between the first tubular member and a wall of the first bore. 
     
     
         8 . The method of  claim 7  wherein the portion of the first expandable tubular member is expanded to a larger diameter prior to the cement curing. 
     
     
         9 . The method of  claim 1  further comprising cementing the second tubular member in place within the second bore. 
     
     
         10 . The method of  claim 1  further comprising the step of expanding a portion of the second tubular member. 
     
     
         11 . The method of  claim 1  further comprising cementing the second drill bit in place within the second bore. 
     
     
         12 . A method of forming a supported bore comprising the steps of: locating a first drill bit on a steerable tool and mounting the steerable tool and first drill bit on a first expandable tubular member, said first expandable tubular member including a deflecting member and means for determining at least one parameter of the bore and the orientation of the drill bit; drilling a first bore to a first depth; pumping cement into an annulus formed between the first tubular member and the wall of the first bore; expanding a portion of the first expandable tubular member to a larger diameter; inserting a second drill bit mounted on a second tubular member within the first tubular member; drilling through a wall portion of the first tubular member at the location of the deflecting member and drilling a second bore to a second depth; and cementing the second tubular member in place within the second bore.