Method and System for Forming a Non-Circular Borehole

Abstract

System and methods for creating shaped, non-circular boreholes in rocks especially for use with geothermal heat pump applications and for increasing wellbore support in applications such as horizontal oil and gas drilling are described. The systems and methods when applied to geothermal heat pumps create an elliptical shaped hole that is optimized for placing heat transfer tubes with a minimum of grout used. The significantly reduced cross-sectional area of the elliptical borehole also increases the overall drilling rate in rock and especially in hard rocks. In horizontal hard-rock drilling, creation of a horizontal non-circular borehole or modification of a circular borehole to a non-circular geometry is used to stabilize the borehole prior to casing insertion, and may also allow the use of lower mud pressures improving drilling rates. The system uses a non-contacting drilling system which in one embodiment uses a supersonic flame jet drilling system with a movable nozzle that swings between pivot points. In a second embodiment the elliptical shaped hole is created by an abrasive fluid or particle bearing-fluid or air jet drill that moves between pivot points. In another embodiment a non-contacting drill can use dual parallel nutating nozzles that create a pair of overlapping circular holes. The non-circular shaped hole is created by either the high temperature flame or water-particle jet or chemically active fluid jet as it removes rock material by erosion, dissolution and or thermal spalling. Modifications of circular boreholes to a generally elliptical shape can also be done using milling or jetting techniques.

1 . A method of increasing the mechanical stability of a portion of an existing circular borehole, comprising:
 providing a means for forming a substantially non-circular-shaped cross-section drill hole in the existing circular borehole; and   using said means to form the substantially non-circular-shaped cross-section drill hole thus limiting uncontrolled breakout in the borehole.   
   
   
       2 .- 8 . (canceled) 
   
   
       9 . The method of  claim 1  wherein said means for forming the substantially non-circular-shaped cross-section drill hole comprises a non-contacting drilling tool. 
   
   
       10 . The method of  claim 1  wherein said means for forming the substantially non-circular-shaped cross-section drill hole comprises a substantially slotted jet nozzle drill head configured to form a jet having a length longer than the jet width 
   
   
       11 . The method of  claim 1  wherein said means for forming the substantially non-circular-shaped cross-section drill hole comprises a flame jet drilling tool. 
   
   
       12 . The method of  claim 11  wherein said means for forming the substantially non-circular-shaped cross-section drill hole comprises a superheated water or steam tool. 
   
   
       13 .- 15 . (canceled) 
   
   
       16 . The method of  claim 1  wherein said means for forming the substantially non-circular-shaped cross-section drill hole comprises a chemical drilling tool using a fluid containing a chemically erosive fluid. 
   
   
       17 . The method of  claim 16  wherein said erosive fluid is a basic or an acidic solution. 
   
   
       18 . The method of  claim 1  wherein said means for forming the substantially non-circular-shaped cross-section drill hole comprises a drill body having a diameter that is smaller than the minimum width of the non-circular hole. 
   
   
       19 .- 22 . (canceled) 
   
   
       23 . A method of forming a drill hole having a substantially non-circular shaped cross-section, comprising:
 forming a circular cross-section bore hole with a first drilling tool; and   forming extended regions on two sides of the circular cross-section bore using a second drilling tool, so as to form two lobes extending from the circular cross-section bore, thus forming said substantially non-circular shaped cross-section.   
   
   
       24 . The method of  claim 23 , wherein said second drilling tool is configured for a milling operation. 
   
   
       25 . The method of  claim 23 , wherein said second drilling tool is configured for a jet drilling operation. 
   
   
       26 . The method of  claim 23 , wherein said drill hole having a substantially non-circular shaped cross-section is a horizontal drill hole. 
   
   
       27 . The method of  claim 23 , wherein said drill hole having a substantially non-circular shaped cross-section is a non-vertical drill hole. 
   
   
       28 . The method of  claim 23 , wherein said first drilling tool is selected from the group consisting of: a rotary bit, an auger, a rotary impact, a percussion or sonic drill, a coiled tubing drill, and combinations thereof. 
   
   
       29 . The method of  claim 23 , wherein said second drilling tool is configured to drill using a process selected from the group consisting of: contact drilling, non-contact drilling, rotary bit, grinding, abrasion, particle abrasion, spallation, sonication, scraping, cutting, melting, and fusing. 
   
   
       30 .- 31 . (canceled) 
   
   
       32 . The method of  claim 23  wherein the second drilling tool operates concurrently with the primary drilling tool. 
   
   
       33 . The method of  claim 23  wherein the second drilling tool operates while the primary drill string is still in the wellbore. 
   
   
       34 . The method of  claim 23 , wherein the second drilling operation occurs during the removal of the drill string of the primary drilling operation. 
   
   
       35 . The method of  claim 23 , wherein the second drilling operation occurs after the removal of the drill string from the primary drilling operation. 
   
   
       36 . The method of  claim 1  further comprising determining the orientation of the stresses in the rock, the orientation of a bottom hole assembly, or the orientation of a bottom hole assembly relative to the stresses, using downhole instrumentation, during the course of forming the substantially non-circular-shaped cross-section drill hole. 
   
   
       37 .- 56 . (canceled) 
   
   
       57 . The method of  claim 1  wherein the substantially non-circular-shaped cross-section drill hole has a L/W ratio greater than 1.0. 
   
   
       58 . The method of  claim 1  wherein the substantially non-circular-shaped cross-section drill hole has L/W ratio between 1.05 and 10. 
   
   
       59 . The method of  claim 1  wherein the substantially non-circular-shaped cross-section drill hole is substantially asymmetric. 
   
   
       60 . The method of  claim 1 , wherein the portion of the existing borehole is significantly horizontal. 
   
   
       61 . The method of  claim 1 , wherein the portion of the existing borehole is significantly vertical. 
   
   
       62 . The method of  claim 1 , wherein the means to form the substantially non-circular-shaped cross-section drill hole comprises hydrothermal spallation. 
   
   
       63 . The method of  claim 1 , further comprising:
 obtaining information of principal stresses in the existing borehole, and   guiding the means to form the substantially non-circular-shaped cross section drill hole to said principal stresses.   
   
   
       64 . The method of  claim 23 , wherein said forming extended regions on two sides of the circular cross-section bore comprises the use of hydrothermal spallation. 
   
   
       65 . The method of  claim 23 , further comprising:
 obtaining information of principal stresses in the existing borehole, and   guiding the second drilling tool to said stresses, thereby relieving the determined stresses.   
   
   
       66 . The method of  claim 36 , further comprising guiding the means to form the substantially non-circular-shaped cross section drill hole to said principal stresses. 
   
   
       67 . A method of reducing uncontrolled breakout in portion of a circularly formed wellbore, comprising
 hydrothermally spalling rock in said portion thereby forming a non-circular shaped cross section of said wellbore.   
   
   
       68 . The method of  claim 65 , wherein said hydrothermally spalling comprises use of a shaped nozzle.