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, said method comprising the steps of:
 locating a first drill bit on a first expandable tubular member having an upper portion of a first diameter and a lower portion of a second, larger diameter, drilling a bore with the drill bit mounted on the first expandable tubular member,   pumping cement into an annulus formed between the expandable tubular member and the wall of the bore; and   expanding the upper portion of the tubular member to a third diameter, greater than the first diameter.   
     
     
         2 . The method of  claim 1 , wherein the third diameter is substantially equal to the second diameter. 
     
     
         3 . A method of forming a supported bore as claimed in  claim 1 , wherein the upper portion of the tubular member is expanded by use of an expansion mandrel forced through the tubular member. 
     
     
         4 . A method of forming a supported bore as claimed in  claim 3 , wherein the mandrel is moved in an upwards direction to expand the tubular member. 
     
     
         5 . A method of forming a supported bore as claimed in  claim 3 , wherein the mandrel is moved in a downwards direction to expand the tubular member. 
     
     
         6 . A method of forming a supported bore as claimed in  claim 3 , wherein the mandrel is substantially conical. 
     
     
         7 . A method of forming a supported bore as claimed in  claim 1 , wherein the tubular member includes a valve member defining a throughbore through which fluid may pass. 
     
     
         8 . A method of forming a supported bore as claimed in  claim 7 , wherein the valve member is a collar. 
     
     
         9 . A method of forming a supported bore as claimed in  claim 7 , wherein the valve member is a float collar. 
     
     
         10 . A method of forming a supported bore as claimed in  claim 3 , wherein the mandrel defines a fluid transmitting throughbore providing a passage for fluid. 
     
     
         11 . A method of forming a supported bore as claimed in  claim 7 , wherein the mandrel is initially located within the lower portion of the tubular member above the valve member. 
     
     
         12 . A method of forming a supported bore as claimed in  claim 7 , wherein the throughbore in the valve member is closable to form a chamber between the valve member and the mandrel. 
     
     
         13 . A method of forming a supported bore as claimed in  claim 12 , wherein the throughbore in the valve member is closed by a plug or dart provided from surface. 
     
     
         14 . A method of forming a supported bore as claimed in  claim 12 , wherein the throughbore in the valve member is closed by a flapper valve. 
     
     
         15 . A method of forming a supported bore as claimed in  claim 12 , wherein the throughbore in the valve member is closed by a ball valve. 
     
     
         16 . A method of forming a supported bore as claimed in  claim 12 , wherein the method further comprises the step of pressurising the chamber formed between the mandrel and the valve member, such that the mandrel is forced through the tubular member to effect expansion of the tubular member. 
     
     
         17 . A method of forming a supported bore as claimed in  claim 16 , wherein by initially pressurising the chamber, the throughbore in the mandrel is closed. 
     
     
         18 . A method of forming a supported bore as claimed in  claim 17 , wherein the throughbore in the mandrel is closed by use of a one way pressure valve. 
     
     
         19 . A method of forming a supported bore as claimed in  claim 17 , wherein the throughbore in the mandrel is closed by use of a flapper valve. 
     
     
         20 . A method of forming a supported bore as claimed in  claim 16 , wherein the chamber is pressurised with a fluid provided from surface, which fluid is pumped through the mandrel and into the chamber. 
     
     
         21 . A method of forming a supported bore as claimed in  claim 12 , wherein the mandrel comprises a pumping mechanism to pump fluid into the chamber. 
     
     
         22 . A method of forming a supported bore as claimed in  claim 12 , wherein a separate pumping unit is utilised to pump fluid into the chamber. 
     
     
         23 . A method of forming a supported bore as claimed in  claim 22 , wherein the separate pumping unit is located adjacent the mandrel. 
     
     
         24 . A method of forming a supported bore as claimed in  claim 23 , wherein the separate pumping unit is located at surface level. 
     
     
         25 . A method of forming a supported bore as claimed in  claim 3 , comprising creating a pressure differential across the mandrel to urge the mandrel through the tubular mandrel. 
     
     
         26 . A method of forming a supported bore as claimed in  claim 25 , wherein pressurised fluid is supplied from surface to create said pressure differential. 
     
     
         27 . A method of forming a supported bore as claimed in  claim 25 , comprising running in a further tubular member to engage the mandrel and supplying pressurised fluid via the further tubular member. 
     
     
         28 . A method of forming a supported bore as claimed in  claim 27 , comprising running said further tubular member following drilling of the bore. 
     
     
         29 . A method of forming a supported bore as claimed in  claim 3 , wherein the mandrel is forced through the tubular member by pulling from the surface. 
     
     
         30 . A method of forming a supported bore as claimed in  claim 29 , wherein the mandrel is pulled through the tubular member by use of a support member. 
     
     
         31 . A method of forming a supported bore as claimed in  claim 30 , wherein the support member is run in following drilling of the bore. 
     
     
         32 . A method of forming a supported bore as claimed in  claim 30 , wherein the support member is a reelable support. 
     
     
         33 . A method of forming a supported bore as claimed in  claim 30 , wherein the support member is a drill pipe string. 
     
     
         34 . A method of forming a supported bore as claimed in  claim 3 , wherein the mandrel is removed from the tubular member once the tubular member has been expanded. 
     
     
         35 . A method of forming a supported bore as claimed in  claim 1 , wherein the method further comprises the step of inserting a second drill bit mounted on a second tubular member within the first tubular member after said first tubular member has been expanded and drilling through a wall portion of the first tubular member and subsequently drilling a second bore. 
     
     
         36 . A method of forming a supported bore as claimed in  claim 35 , wherein once the second bore is drilled to the required depth, cement is pumped into an annulus formed between the wall of the second bore and the second tubular member. 
     
     
         37 . A method of forming a supported bore as claimed in  claim 35 , wherein the first expandable tubular member includes a deflecting member, which deflecting member, in use, deflects or guides the second drill bit towards a wall portion of the first tubular member to be drilled. 
     
     
         38 . A method of forming a supported bore as claimed in  claim 37 , wherein the deflection member is located below the valve member and the mandrel. 
     
     
         39 . A method of forming a supported bore as claimed in  claim 35 , wherein the second tubular member is expandable and a portion thereof may be expanded to a larger diameter once the second bore has been drilled to the required depth. 
     
     
         40 . A method of forming a supported bore as claimed in  claim 39 , wherein the second tubular member is expanded before cement is pumped into the annulus between the second bore wall and the second tubular member. 
     
     
         41 . A method of forming a supported bore as claimed in  claim 39 , wherein the second tubular member is expanded after cement is pumped into the annulus. 
     
     
         42 . A method of forming a supported bore as claimed in  claim 1 , wherein the volume of cement pumped into the annulus is selected such that the annulus is substantially filled with cement when the upper portion of the expandable tubular member has been expanded. 
     
     
         43 . A drilling assembly comprising a first drill bit mounted on a first expandable tubular member, wherein said first expandable tubular member includes an upper portion of a first diameter and a lower portion of a second, larger diameter.