Method of drilling a borehole in an earth formation

Abstract

A borehole is drilled in an earth formation using consecutive steps of: (a) drilling a first open hole section of a borehole, employing a first drill string extending into the borehole from a surface on the earth, to a casing setting depth; (b) retrieving the first drill string from the borehole to the surface; (c) everting a tubular element in the open hole section, wherein axially advancing an inner tube section of the tubular element into the borehole through and in relative axial movement to an outer tube section of the same tubular element; (d) creating an annular seal between the outer tube section and an inward facing wall of the borehole; (e) inserting a second drill string through the inner tube section into the borehole; and (f) further deepening the borehole by drilling a second open hole section of the borehole.

What is claimed is: 
     
         1 . A method of drilling a borehole in an earth formation, comprising consecutive steps of:
 (a) drilling a first open hole section of a borehole, employing a first drill string extending into the borehole from a surface on the earth, to a casing setting depth;   (b) retrieving the first drill string from the borehole to the surface;   (c) everting a tubular element in the open hole section, which tubular element comprises an inner tube section and an outer tube section connected to each other in a lower bending zone, wherein the inner tube section runs through the outer tube section and wherein a wall of the tubular element is, in said lower bending zone at a lower end of the inner tube section, induced to bend radially outward and in axially reversed direction so as to form the outer tube section which thereby is everted compared to the inner tube section, wherein said everting comprises axially advancing the inner tube section into the borehole through the outer tube section in relative axial movement compared to the outer tube section;   (d) creating an annular seal between the outer tube section and an inward facing wall of the borehole;   (e) inserting a second drill string through the inner tube section into the borehole;   (f) further deepening the borehole by drilling a second open hole section of the borehole, employing the second drill string, to a second depth that is deeper than the casing setting depth.   
     
     
         2 . The method of  claim 1 , wherein during step (f) the second drill string is advanced into the borehole as the borehole is being drilled, whereas the tubular element is kept stationary whereby keeping the lower bending zone at a fixed depth. 
     
     
         3 . The method of  claim 2 , wherein the inner tube is temporarily secured at or near the surface for at least the duration of step (f). 
     
     
         4 . The method of  claim 1 , wherein step (f) is continued until reaching a further case setting depth; and subsequently carrying out step (b) again with respect to the second drill string, after which further everting the tubular element into the second open hole section, comprising axially further advancing the inner tube section into the borehole through the outer tube section in relative axial movement with the outer tube section. 
     
     
         5 . The method of  claim 1 , wherein the tubular element is a seamless tubular element. 
     
     
         6 . The method of  claim 4 , wherein said further everting comprises extending the inner tube section with an extension tube by sealingly abutting the extension tube to a top rim of the inner tube. 
     
     
         7 . The method of  claim 6 , wherein said sealingly abutting comprises welding a bottom rim of said extension tube to the top rim of the inner tube. 
     
     
         8 . The method of  claim 6 , wherein the tubular element and the extension tube are both seamless. 
     
     
         9 . The method of  claim 4 , wherein creating a second annular seal between the outer tube section and an inward facing wall of the borehole in the second open hole section. 
     
     
         10 . The method of  claim 1 , wherein the tubular element is provided in the form of coiled tubing, and wherein the inner tube section extends to a coiled-up portion of the coiled tubing, and wherein step (c) comprises supplying the inner tube by uncoiling the coiled tubing from the coiled-up portion while axially advancing the inner tube section into the borehole. 
     
     
         11 . The method of  claim 1 , wherein after completing step (c) and prior to step (e) the inner tube section is circumferentially cut off whereby removing at least a part of the tubular element that is exposed at the earth surface and retaining a part of the inner tube section below a cut rim. 
     
     
         12 . The method of  claim 1 , wherein after completing step (a) and prior to step (d) a hardening liquid substance is introduced into the borehole, and wherein step (d) comprises allowing hardening of the liquid substance while at least the lower bending zone is submerged into the hardening liquid substance. 
     
     
         13 . The method of  claim 12 , wherein the hardening liquid substance is retarded to allow time to complete step (c) before hardening of the liquid substance is completed. 
     
     
         14 . The method of  claim 1 , wherein the second drill string comprises an under-reamer having a gauge diameter larger than an inside bore diameter of the inner tube section to drill the second open hole section to a bore diameter that is larger than the inside bore diameter of the inner tube section.