System and method for geothermal well installation

Abstract

A system and method are provided for installing a well for a borehole heat exchanger. The method includes drilling a hole formation to a predetermined depth relative to a ground surface, including operating a bottomhole assembly (BHA) including a drill bit supported at a bottom end of a cable positioned within a flexible tube. After drilling the hole formation to a predetermined depth, the BHA is retracted through the flexible tube to remove the BHA from the hole formation while the flexible tube remains in the hole formation.

1 . A method for installing a well for a borehole heat exchanger, the method comprising:
 drilling a hole formation to a predetermined depth relative to a ground surface, drilling the hole formation including operating a bottom hole assembly (BHA) including a drill bit supported at a bottom end of a cable, such as a wireline, the cable positioned within a flexible tube; and   after drilling the hole formation to the predetermined depth, retracting the BHA through the flexible tube to remove the BHA from the hole formation while the flexible tube remains in the hole formation.   
     
     
         2 . The method of  claim 1 , further comprising, after drilling the hole formation to the predetermined depth and prior to retracting the BHA, operating a latch to uncouple the BHA from a lower end of the flexible tube. 
     
     
         3 . The method of  claim 1 , further comprising, after retracting the BHA, securing the flexible tube within the hole formation by inserting cement between an outer surface of the flexible tube and an inner surface of the hole formation. 
     
     
         4 . The method of  claim 1 , further comprising securing the flexible tube within the hole formation by heating the flexible tube and moving a mechanical conforming device through the flexible tube to deform the flexible tube radially outward against a surface of the hole formation, wherein the mechanical conforming device is optionally part of the BHA. 
     
     
         5 . The method of  claim 1 , further comprising, after retracting the BHA, inserting at least one inner tube through the flexible tube to form the borehole heat exchanger. 
     
     
         6 . The method of  claim 5 , wherein inserting an inner tube through the flexible tube includes inserting a bottom tube sealing assembly to facilitate fluid circulation between the flexible tube and the inner tube in a closed loop manner. 
     
     
         7 . The method of  claim 1 , wherein drilling the hole formation includes drilling the hole formation with a reamer in an extended state in which an outer diameter of the reamer is larger than a diameter of the flexible tube, wherein the BHA optionally includes the reamer,
 the method further comprising, after drilling the hole formation to the predetermined depth and prior to retracting the BHA, moving the reamer to a collapsed state in which the outer diameter of the reamer is smaller than the diameter of the flexible tube.   
     
     
         8 . A system for installing a well for a ground source heat pump application, the system comprising:
 a cable, such as a wireline, having a lower end;   a bottom hole assembly (BHA) supported adjacent the lower end of the cable, the BHA including a drill bit operable to excavate a hole; and   a flexible tube extending around the cable, the lower end of the flexible tube being removably coupled to the BHA, wherein, while the flexible tube is coupled to the BHA, the flexible tube is movable with the BHA as the drill bit excavates the hole, and, while the flexible tube is uncoupled from the BHA, the flexible tube remains within the hole as the BHA is removed from the hole.   
     
     
         9 . The system of  claim 8 , wherein the flexible tube is made from polyethylene. 
     
     
         10 . The system of  claim 8 , wherein the BHA is removably coupled to the flexible tube by a latch. 
     
     
         11 . The system of  claim 8 , wherein the BHA further includes a reamer the reamer being movable between an extended state and a collapsed state, an outer diameter of the reamer being larger than a diameter of the flexible tube in the extended state, the outer diameter of the reamer being smaller than the diameter of the flexible tube in the collapsed state. 
     
     
         12 . The system of  claim 8 , wherein, while the flexible tube is uncoupled from the BHA, the cable and the BHA are retractable through the flexible tube to leave the flexible tube within the hole. 
     
     
         13 . The system of  claim 12 , further comprising an inner tube insertable into the flexible tube when the BHA is removed from the hole. 
     
     
         14 . The system of  claim 13 , further comprising a bottom tube sealing assembly to facilitate fluid circulation between the inner tube and a space positioned between the flexible tube and an outer surface of the inner tube in a closed loop manner. 
     
     
         15 . The system of  claim 8 , further comprising a heating element for heating the flexible tube; and a mechanical conforming device, the mechanical conforming device movable through the flexible tube to deform the flexible tube radially outward against a surface of the hole. 
     
     
         16 . The system of  claim 15 , wherein the heating element and the mechanical conforming device are arranged on the BHA. 
     
     
         17 . A borehole heat exchanger system comprising:
 an outer tube positioned within a drilled hole formation, the outer tube comprising a flexible thermoplastic material;   an inner tube positioned within the outer tube to form a coaxial configuration; and   a closed loop circuit formed between the outer tube and the inner tube configured to circulate heat transfer fluid between a ground source heat pump and the drilled hole formation.   
     
     
         18 . The borehole heat exchanger system of  claim 17 , wherein the outer tube is secured within the drilled hole formation by cement positioned between an outer surface of the outer tube and an inner surface of the drilled hole formation. 
     
     
         19 . The borehole heat exchanger system of  claim 17 , wherein the outer tube is deformed radially outward against a surface of the drilled hole formation to secure the outer tube within the drilled hole formation. 
     
     
         20 . The borehole heat exchanger system of  claim 17 , further comprising a bottom sealing assembly positioned at a lower end of the inner tube and configured to direct fluid circulation between the inner tube and an annular space between the outer tube and the inner tube.