U.S. patent application number 11/691445 was filed with the patent office on 2008-04-24 for method and system for forming a non-circular borehole.
This patent application is currently assigned to Potter Drilling, LLC. Invention is credited to James Robert Basler, Jared Michael Potter, Robert Marshall Potter, Thomas Waller Wideman.
Application Number | 20080093125 11/691445 |
Document ID | / |
Family ID | 38541862 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080093125 |
Kind Code |
A1 |
Potter; Jared Michael ; et
al. |
April 24, 2008 |
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.
Inventors: |
Potter; Jared Michael; (San
Carlos, CA) ; Potter; Robert Marshall; (Rio Rancho,
NM) ; Basler; James Robert; (Redwood City, CA)
; Wideman; Thomas Waller; (Milton, MA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Potter Drilling, LLC
Redwood City
CA
|
Family ID: |
38541862 |
Appl. No.: |
11/691445 |
Filed: |
March 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60786456 |
Mar 27, 2006 |
|
|
|
Current U.S.
Class: |
175/67 ;
175/91 |
Current CPC
Class: |
F24T 2010/53 20180501;
E21B 7/001 20130101; Y02E 10/125 20130101; Y02E 10/10 20130101;
F03G 7/04 20130101; F24T 10/15 20180501 |
Class at
Publication: |
175/067 ;
175/091 |
International
Class: |
E21B 7/18 20060101
E21B007/18 |
Claims
1. A method of forming a drill hole having a substantially
non-circular shaped cross-section, comprising: providing a means
for forming the substantially non-circular-shaped cross-section
drill hole; and using said means to form the substantially
non-circular-shaped cross-section drill hole.
2. The method of claim 1 wherein the drilled hole is formed in
rocks for the purpose of preparing the rocks for a geothermal heat
pump application.
3. The method of claim 1 wherein the drilled hole is formed in
rocks for the purpose of increasing the mechanical stability of the
borehole.
4. The method of claim 1 wherein the drilled hole is formed in
rocks for the purpose of stabilizing the formation during the
drilling and completion of a well for oil and gas exploration or
production.
5. The method of claim 1 wherein said means for forming the
substantially non-circular-shaped cross-section drill hole
comprises a swivel mechanism configured to swivel a drill head
nozzle assembly.
6. The method of claim 5 wherein the swivel mechanism is configured
to swivel the drill head along an arc in a direction transverse to
a longitudinal line aligned along the drill hole depth.
7. The method of claim 5 wherein the throw of the swivel mechanism
is configurable to control the length of the elliptical portion of
the drill hole.
8. The method of claim 5 wherein the rate of movement of the drill
head in a swiveling motion is adjustable.
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 1 wherein said means for forming the
substantially non-circular-shaped cross-section drill hole
comprises a superheated water or steam tool.
13. The method of claim 1 wherein said means for forming the
substantially non-circular-shaped cross-section drill hole
comprises an abrasive water jet tool.
14. The method of claim 13 wherein the abrasive water jet includes
entrained particles.
15. The method of claim 1 wherein said means for forming the
substantially non-circular-shaped cross-section drill hole
comprises a particle jet drill using mud as the drilling fluid.
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. The method of claim 1 wherein said means for forming the
substantially non-circular-shaped cross-section drill hole
comprises a drilling tool having a dual nutating drilling
nozzles.
20. The method of claim 19 wherein said drilling tool is configured
to drill using particulates delivered with a high velocity
fluid.
21. The method of claim 1 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a drilling tool having a dual rotating drilling
nozzles.
22. The method of claim 21 wherein said drilling tool is configured
to drill using particulates delivered with a high velocity
fluid.
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.
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. The method of claim 23, wherein a supply of power for the
second drilling tool is derived from the rotation of the first or
second drilling tool, hydraulic flow of fluids, air flow,
electrical means, thermal means, or chemical means.
31. The method of claim 30 wherein the hydraulic flow of fluids
comprises flow of circulating fluids or muds.
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 wherein downhole instrumentation is used
to determine the orientation of the stresses in the rock, the
orientation of the BHA, or the orientation of the BHA relative to
the stresses during the course of producing the non-circular well
bore.
37. A drilling rig for forming a drill hole having a substantially
non-circular-shaped drill hole cross-section, comprising: a
drilling support system configured for connection with a drill
head; and a drill head configured for connection with the drilling
support system having a means for forming the substantially
non-circular-shaped drill hole cross-section.
38. The rig of claim 37 wherein the rig is configured to form a
drill hole in rocks for the purpose of preparing the rocks for a
geothermal heat pump application.
39. The rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a swivel mechanism configured to swivel a drill head
nozzle assembly.
40. The drilling rig of claim 39 wherein the swivel mechanism is
configured to swivel the drill head along an arc in a direction
transverse to longitudinal line aligned along the drill hole
depth.
41. The drilling rig of claim 39 wherein the throw of the swivel
mechanism is configurable to control the length of the non-circular
portion of the drill hole.
42. The drilling rig of claim 39 wherein the rate of movement of
the drill head in a swiveling motion is adjustable.
43. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a non contacting drilling tool.
44. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a slotted jet nozzle drill head configured to form a jet
having a length longer than the jet width.
45. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a flame jet drilling tool.
46. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a superheated water or steam tool.
47. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises an abrasive water jet tool.
48. The drilling rig of claim 47 wherein the abrasive water jet
includes entrained particles.
49. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a particle jet drill using mud as the drilling fluid.
50. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a chemical drilling tool using a fluid containing a
chemically erosive fluid.
51. The drilling rig of claim 50 wherein said erosive fluid is a
basic or an acidic solution.
52. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a drill body having a diameter that is smaller than the
minimum width of the elliptic hole.
53. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a drilling tool having a dual nutating drilling
nozzles.
54. The drilling rig of claim 53 wherein said drilling tool is
configured to drill using particulates delivered with a high
velocity fluid.
55. The drilling rig of claim 37 wherein said means for forming the
substantially non-circular-shaped drill hole cross-section
comprises a drilling tool having a dual rotating drilling
nozzles.
56. The drilling rig of claim 55 wherein said drilling tool is
configured to drill using particulates delivered with a high
velocity fluid.
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.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 60/786,456, filed Mar. 27, 2006 whose teachings are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates in general to the formation of
intentionally non-circular boreholes. These non-circular boreholes
may be shaped for optimized use in a specific system or
application, such as underground heat exchange systems, or they may
be formed as a means to stabilize the borehole during the drilling,
casing, and completion or in operation.
[0003] Most conventional and non-conventional drilling techniques
are designed to produce boreholes that are substantially circular.
In some formations, such as hard rocks with primary stresses
oriented vertically, circular boreholes are inherently unstable
which might be caused by the non-uniform stress conditions in the
rock or from a general weakness in the rock. Once a circular hole
is produced, these stresses may cause portions of the formation to
break from the wall, often referred to by those skilled in the art,
and herein referred to, as "break-out". This uncontrolled break-out
often occurs during or sometime after the extraction of the drill
string, including during the insertion of the casing, and can cause
significant disruptions in the drilling process and completion
process. Uncontrolled break-out can be a particular problem in bore
sections which have a horizontal or non-vertical orientation.
Break-out often creates a substantially non-circular or elliptical
cross-section, with the longer axis of the ellipse often in a
substantially horizontal plane, or parallel to the earth's surface.
To prevent the uncontrolled break-out from occurring, it would be
advantageous to be able to drill or create a non-circular bore, or
modify a bore so as to be non-circular, in an orientation that
partially relieved the stresses in the formation (e.g. see Bjorn
Lund, 2000; Crustal stress studies using micro earthquakes and
boreholes, Comprehensive summaries of Uppsala dissertations from
the faculty of science and technology, 517, 75 pp, Uppsala
University, Sweden)
[0004] There are also specific applications that would benefit from
non-circular holes with reduced tendency towards uncontrolled
break-out. These applications may include geothermal power
generation, such as enhanced or engineered geothermal systems
(herein referred to as EGS) and hot dry rock (herein referred to as
HDR), or applications where the bore hole will be left unsupported
for extended periods (minutes, hours, or days), such as in oil and
gas exploration and production (herein referred to as oil and gas
E&P) operations, or in situations where the wellbore will be
left unsupported indefinitely, such as in an uncased wellbore. An
uncased wellbore may have an inner surface that comprises the
formation, or one that is substantially comprised of fused rock,
ice, a layer of a non-metallic material, such as a thermoplastic,
thermoset, composite or ceramic, or a layer of fused metallic
material. In addition to EGS-HDR and oil and gas E&P, other
conventional applications could benefit by the drilling of
non-circular boreholes with reduced tendency towards break-out,
including, but not limited to, water well drilling, trenchless pipe
installation, sewer and municipal system construction, resource
mining, chemical disposal wells, CO.sub.2 or nuclear storage wells,
downhole chemical reactions (such as, but not limited to, municipal
waste oxidation or biofermentation), bores in ice, or wells for
scientific or geologic study, including test holes or secondary
holes used for measurements in the above or other operations and
applications.
[0005] Another application for non-circular boreholes is the
installation of underground heat exchange systems for geothermal or
ground source heat pumps (herein referred to interchangeably as GHP
or GSHP). GHP's are used throughout the world as a means to
effectively heat and cool houses and businesses through a heat
exchange loop system located in the earth. A typical heat exchange
loop may be comprised of tubing installed in holes 150 feet to 500
feet deep which circulates fluids and extracts or disposes of heat
into the ground. The number of holes used depends on the heat
exchange requirements for the complete system. In some newer
configurations, the drill holes start in the same general location
but then divert at approximately a 30 degree angle from the
vertical, forming a cone like array, as shown in FIG. 1a. This cone
shape creates a compact connection point for all of the heat
exchange tubes. Many locations, however, use numerous vertical
holes, usually aligned in rows, with separation of about 20 feet,
as shown in FIG. 1b.
[0006] Typically, 4 to 6 inch diameter holes are required in GHP
applications when reasonably large heat flow lines need to be
installed. Inside the holes, flow lines are inserted which
typically range from 0.75 inch to 1.25 inches in inner diameter. If
too small a hole is drilled, it is difficult to insert the tubes
into the hole as well as get a good placement of grout into the
hole and around the tube. A less than optimum grout placement may
create a condition where bubbles can get entrained in the grout
reducing the effectiveness of the heat exchange system. The
in-flowing and out-flowing lines must be adequately separated to
prevent the out-going line from transferring heat back into the
in-coming line; in a sense, short circuiting the desired heat
transfer to the earth.
[0007] GHP's are well known, and there are a number of standard
techniques of creating the holes for these systems. Conventional
drilling technologies have traditionally been employed for the
drilling of holes for geothermal systems including, but not limited
to, auger, rotary bit, rotary impact (hammer), percussion, and
sonic drilling methods. However, no single system has yet been
found to be ideal for drilling in all rock types. Furthermore, any
of these technologies using a single bit cannot create a
substantially non-circular hole because the required rotation and
contact of the drill bit with the rock during the drilling process
inherently produces a substantially circular profile.
[0008] Drilling large holes for purposes such as installing heat
exchange loops can be especially problematic in hard rock. As used
herein, "rock" may loosely refer to any material in the well bore,
including loose and unconsolidated soils, consolidated soils,
clays, sands, conglomerates, soft or hard rock, or any formation of
any naturally occurring composition. As used herein, a hard rock
refers to a rock that is well consolidated and typically has a
number of hard minerals such as feldspars and quartz and lacks
significant amount of clays. Such a hard rock can have a
compressive strength of about or greater than 10 ksi. Also as used
herein, a large diameter hole refers to a hole having a diameter
that is larger than about 5 inches. Drilling holes in hard rock is
a time consuming and costly process. In fact, if a large number of
holes in the hard rocks are required, the drilling costs can exceed
the costs of the rest of the heat pump and flow lines combined. In
addition, hard rocks typically have lower fluid contents so that
heat exchange from the tubing to the rock is reduced and more flow
lines may be needed compared to soft rock for the same amount of
heat exchange.
[0009] Hard rock drilling has traditionally been accomplished by
several different methods, including impact hammer drill or rotary
drilling. Drill rates for these techniques in hard rock can be as
slow as 10 feet per hour or less for larger diameter holes.
Non-contact drilling technologies such as flame jet spallation,
hydrothermal spallation, particle impact drilling, or water jet
drilling (with or without abrasive particulates) have the advantage
of being able to drill faster in hard rocks. Non-contact drilling
is herein defined as technologies which do not require contact
between the bottom hole assembly and rock in order to remove the
rock by the intended means, but may use the rock wall for secondary
purposes, such as orientation, stabilization, propulsion, or the
like. For example, tests conducted in the field have shown drilling
rates of more than about 30 feet/hr rates for 8 inch holes using
air-fuel flame jet combustion drills. A summary of some of the
known non-contact drilling techniques is provided below.
[0010] Several flame jet drilling techniques are known. For
example, U.S. Pat. No. 3,045,766 discloses a suspension type rotary
piercing process and apparatus and describes a blowpipe type rotary
flame jet system suspended from a cable to allow for vertical jet
drilling. U.S. Pat. No. 3,103,251 is directed to a flame cutting
method and describes a flame cutting process improved by the
addition of air or inert gas to the jet to increase drill rates.
U.S. Pat. No. 3,182,734 is directed to a fusion piercing or
drilling machine and discloses a system that uses a rotating
combustion chamber in conjunction with outside scrapers to spall
and melt rock to create a clean, consistent, circular bore. U.S.
Pat. No. 3,322,213 is directed to thermal mechanical mineral
piercing and discloses a rotating combination grinding and flame
jet drill system for creating consistent, round bores through a
process of thermal spallation and wear. U.S. Pat. No. 3,476,194 is
directed to flame jet drilling and discloses a method for creating
smaller holes by adding coolant closer to the flame outlet to
diminish the thermal process away from the flame jet tool. U.S.
Pat. No. 4,066,137 is directed to a flame jet tool for drilling
cross holes and discloses a method for creating a side bore using
thermal flame jet technology. U.S. Pat. No. 4,073,351 is directed
to burners for a flame jet drill and discloses a technique for
mixing both flame jet and water jets into the same drill head with
different options for the shape and orientation of the nozzles and
jets. A rotating head is used in this design which creates circular
shaped holes. However, none of the known flame jet drilling
techniques suggests shaped or non-circular cross-section holes.
[0011] It is known that superheated steam or a high pressure fluid
may also be used for drilling. However, such known techniques have
only been used for the drilling of round holes. Several water jet
drilling techniques are known. For example, U.S. Pat. No. 5,402,855
directed to coiled tubing tools for jet drilling of deviated wells
describes a jet nozzle drill for creating deviated (e.g., off
vertical) wellbores from a cased vertical well. This patent
provides a discussion of how to shift the high pressure nozzle to
create a tilt in the jet system. This patent also provides a
discussion of how the nozzle is shifted using a series of plungers
tied to a control system and a flexible rubber boot assembly. U.S.
Pat. No. 4,369,850 uses a rotating fluid jet assembly with multiple
nozzles to create circular holes. U.S. Pat. No. 3,576,222 discloses
a drill bit with hydraulic action using a number of nozzles and a
rotating head for circular shaped hole generation. U.S. Pat. No.
5,111,891 describes a technology for creating a biasing in a
wellbore for changing direction using a water jet for soil erosion.
When rotated, the nozzle creates a circular hole. When the nozzle
is stopped from rotating, it cuts a side bore path to allow the jet
to relieve the adjacent area and enable the drill to change
directions. U.S. Pat. No. 4,930,586 discloses a hydraulic drilling
system with a single outlet jet and a series of four side jets
which enable the control of the drilling direction. U.S. Pat. No.
5,944,123 discloses a system for creating holes using a water jet
technique with capabilities for controlling orientation and
rotation of the head. U.S. Pat. No. 4,871,037 discloses a
combination rotating mechanical grinding and jet nozzle drilling
system. However, none of these water jet drilling techniques
suggest the creation of a non-circular shaped borehole or a shaped
nozzle for the same.
[0012] While it is known that particle impact drilling may also be
used to form boreholes using either water or mud suited to well
drilling, and while such a known technique has been used with a
rotating head and for creating circular holes, there is no
suggestion in this area for creating shaped or non-circular holes.
For example, U.S. Pat. No. 6,386,300 describes the use of a
particle impact process using small metal spheres to increase
drilling rates in traditional rotating drilling systems as well as
a system to remove the spheres from the drilling mud. U.S. Pat. No.
4,768,709 describes a system for using individual fluid particulate
jets to create channels and notches into existing boreholes to
improve blasting characteristics.
[0013] Another known technology uses a supercritical fluid for the
drilling task. Such known techniques create circular holes. For
example, U.S. Pat. No. 6,347,675 uses CO.sub.2 as the drilling
fluid in a conventional coil tube drill system and as a jet fluid
for enhanced drilling rates. The '675 patent describes a system for
providing and separating CO.sub.2 from the drilling fluid. There is
no disclosure or suggestion for the generation of shaped or
non-circular holes.
[0014] Another known drilling technology involves chemical drilling
systems. Such known chemical drilling systems also create circular
holes and do not suggest techniques for creating shaped or
non-circular holes. In particular, the known chemical drilling
references are related to using chemical drills to create holes in
rocks and removing the reaction products from the hole. For
example, U.S. Pat. No. 6,742,603 discloses using a high temperature
sodium hydroxide (NaOH) fluid stream to etch a hole in rock. U.S.
Pat. No. 4,431,069 describes a system that uses acidic or basic
slurries to drill boreholes; the '069 patent also describes some
aspect of directing the flow jet to change direction in order to
create a directional, yet circular, borehole. U.S. Pat. No.
6,772,847 discusses using acids or other chemicals to create bore
holes and suggests creating a cloverleaf shaped hole by using
multiple nozzles. A cloverleaf-shaped borehole is not a suitable
borehole profile for applications such as heat exchanger tube
installations, where a minimal amount of rock removal is desired,
nor does it help stabilize the borehole. It may also cause greater
head losses for flowing fluids.
[0015] In connection with drilling, tube installation and grout
placement for geothermal heat pump applications, a few patents are
summarized below. For example, U.S. Pat. No. 5,590,715 discloses a
system for placing heat loops in place and then grouting them using
a separate grout filling line. Published Application No.
2005/0139353 describes a system for installing heat loops in
conjunction with sonic drilling techniques. U.S. Pat. No. 4,286,651
discusses a technique for driving a pipe into the ground to install
shallow geothermal heat loops with a circular design drive pipe.
All references discussed above are incorporated by reference
herein.
[0016] However, there still exists a need for drilling boreholes
where the preferred cross-sectional geometry is non-circular. There
are also exist a need for forming boreholes having a non-circular
hole geometry that can prevent or reduce break-outs from the
wellbore.
BRIEF SUMMARY OF THE INVENTION
[0017] The present invention describes the benefits, methods and
systems for creating non-circular, generally elliptical, oval or
eccentric shaped holes. The embodiments of the present invention
can be applied to the creation of non-circular boreholes or
modification of circular boreholes to a more non-circular shape.
Certain aspects of the present invention are particularly well
suited for making non-circular holes in hard rock.
[0018] A substantially non-circular hole may help stabilize the
well bore and prevent break outs. A substantially non-circular hole
may also facilitate the installation or operation of a system, such
as in the installation of piping for ground source heat pumps. A
substantially elliptical hole provides an improved geometry for
heat exchange in the ground source heat pump piping loops while
also enabling a much faster and more efficient drilling that does
not suffer from the shortcomings of the prior techniques.
[0019] In one aspect the present invention provides a system and
method for creating shaped drilling holes in rocks especially for
the intention of stabilizing the wellbore. The system can create an
elliptical shaped hole that intentionally reduces the stresses in
the formation around the bore, limiting uncontrolled break-out.
Break-out is a process in which rock breaks from the wall of the
wellbore, creating a non-circular and substantially elliptical
cross-section, often with the longer axis in a substantially
horizontal orientation, in order to relieve the stresses in the
formation around the well-bore. Break-out may be particularly
severe in significantly horizontal or non-vertical portions of the
wellbore. Breakout can be caused by significant non-uniform stress
concentration in the unsupported borehole resulting in localized
shear failure at two opposite nodes in a direction normal to the
main stress direction. Once the break-out occurs, the borehole has
a more stable geometry but the material generated by the small
scale collapse can cause major complications, delays, and expenses
in the drilling, casing and completion of wells. By intentionally
reshaping or ovalizing the hole under controlled conditions or
circumstances, the problems caused by uncontrolled break-out can be
reduced or mitigated. It is particularly attractive to
intentionally create an oval hole during the actual drilling or
just after the drilling operation (such as by a selective milling
procedure or spallation or erosion) so that the rock which is cut
from the wellbore to form the non-circular cross-section can be
removed as part of the cuttings.
[0020] Alternatively, the non-circular hole may be used for
optimized drilling, placing and grouting of tubing such as, but not
limited to, heat exchange loops. The significantly reduced
cross-sectional area of the elliptical borehole increases the
overall drilling rate by reducing the amount of material that must
be removed by as much as 30-40 percent for the same tube to tube
separation of heat exchange loops. The shape of the hole is optimum
for heat transfer from the ground and for minimizing heat transfer
from the inlet to outlet tubes. The shape of the hole also requires
the least amount of grout to be used in the completion of the
system. However, it should be realized that non-circular boreholes
may find use in various other applications such as, but not limited
to, the installation of parallel piping, tubing, conduit, cables or
the like.
[0021] One system for drilling non-circular holes uses a
non-contacting drilling system which in one embodiment uses a
supersonic flame jet drilling system with a movable nozzle. In one
embodiment the non-circular shaped hole is created by an abrasive
fluid or particle bearing-fluid jet drill. A defined herein, a
fluid is any substance that is capable of flow, including liquids,
gases, and supercritical fluids. The fluid used in the fluid jet
drill can be water, drilling mud, or other fluids such as
supercritical carbon dioxide (CO.sub.2) and fluids that erode the
rock chemically using basic or acidic chemicals (such as sodium
hydroxide, or other bases, or hydrofluoric or other acids) in
solution. In another embodiment, a non-contacting drill can be used
that uses a high velocity air stream with suspended or entrained
particulates as the abrasive drilling means. A shaped jet outlet
nozzle may also be used to create the novel asymmetric erosion
shape. The non-circular shaped hole is created by either the high
temperature flame, high temperature steam or water, water-particle
jet or chemically active fluid jet as it removes rock material by
erosion, dissolution and/or thermal spalling.
[0022] For a further understanding of the nature and advantages of
the invention, reference should be made to the following
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1a is an exemplary schematic diagram of a geothermal
heat pump setup showing multiple shallow drill holes in an
off-vertical configuration.
[0024] FIG. 1b is an exemplary schematic diagram of a geothermal
heat pump setup showing multiple vertical boreholes in a line.
[0025] FIG. 2 is an exemplary diagram showing a heat pump flow line
as well as grout in the ground.
[0026] FIG. 3a is an exemplary cross-sectional view of a circular
hole.
[0027] FIG. 3b is an exemplary cross-sectional view of a long width
elliptical hole produced in accordance with the embodiments of the
present invention.
[0028] FIG. 3c is an exemplary cross-sectional view of a short
width non-circular hole produced in accordance with the embodiments
of the present invention.
[0029] FIG. 3d is an exemplary cross-section view of a shaped hole
with an even longer aspect ratio that can accommodate several of
the flow tubes in parallel or in a parallel plane.
[0030] FIG. 3e is a transverse view corresponding to FIG. 3d.
[0031] FIG. 4 is an exemplary schematic diagram of a flame jet
drilling system for shallow non-circular holes, in accordance with
one embodiment of the present invention.
[0032] FIG. 5a is an exemplary diagram of a jet drill head swivel
drilling system in accordance with one embodiment of the present
invention for drilling a non-circular borehole. FIG. 5b is a top
view of FIG. 5a.
[0033] FIG. 6a is an exemplary diagram of a shaped nozzle drilling
system for generating elliptical shaped boreholes without swiveling
using flame or fluid jets, in accordance with one embodiment of the
present invention. FIG. 6b is a top view of FIG. 6a.
[0034] FIG. 7a is an exemplary diagram of a dual nutating (e.g.,
wobbling or rotating) nozzle particle impact drilling system with a
detailed view shown in FIG. 7b and the generally elongate
overlapping circular borehole shape that results from this type of
drilling method shown in FIG. 7c.
[0035] FIG. 8a is an exemplary diagram of a horizontal circular
borehole with the principal stress in the vertical direction and
horizontal regions where breakout can occur.
[0036] FIG. 8b is an exemplary diagram of a generally elliptical
shape created from the circular bore using a borehole milling
technique.
[0037] FIG. 8c is an exemplary diagram of a version of an
elliptical shape with more pronounced milled or eroded lobes.
[0038] FIG. 8d is an exemplary diagram of a shaped borehole using a
borehole milling technique.
DETAILED DESCRIPTION OF THE INVENTION
[0039] FIGS. 1a and 1b show the general layout of a geothermal heat
pump system which is one such system where oval (e.g.,
non-circular) boreholes may be beneficial. It should be noted that
there exist a number of different ways for locating the boreholes
in such a system, and that the general layout of the hole
orientation is not critical to the disclosed embodiments of the
present invention. In the particular version shown, the heat
exchange drill holes are oriented outward from a more or less
central point in an excavated trench 2 where the heat exchanger
tubes are connected together into a manifold system 3. The
out-flowing 4 and in-flowing 5 tubes or pipes are connected to the
manifold system 3. The holes are directed from substantially
central location to simplify the attachment of the flow tubes to a
manifold and to minimize the damage to the terrain around the drill
site. A trench is typically used to hide the connection holes and
tubing. The flow tubes are typically connected in parallel to the
manifold system. The flow tubes are installed after drilling and
thereafter a typically mineral-based grout is pumped into the
wellbore to insulate the tubes from one another and to provide for
improved contact between the tubes and the rock, as well as to
prevent the thermal short circuiting by fluid around the heat flow
tubes. The wellbore detail is described in conjunction with FIG. 2
which shows a detail view of the heat tube in the ground showing
the in-flow 6 and out-flow tubes 7, the grout 8 filling the region
between the tubes with the wellbore 9 including the surrounding
earth 10. The rounded connection tube 11 between in-flow and
out-flow tubes is attached by a union connection 12.
Hole Shape
[0040] FIG. 3a shows a cross-sectional drawing of a circular hole
showing the borehole 13, earth 14 and heat exchange tube 15. FIGS.
3b-c show two elliptical holes of different length to width ratios
(L/W or L:W) showing the elliptical holes 16 and 17. FIGS. 3b-c
also shows the ability of varying the length and width of the hole
to suit the tube geometry. Depending on the size of the flow tubes
and the proximity of the connections of the tubes, a smaller or
larger hole width or length to width ratio can be drilled. In a
typical installation, this novel non-circular cross-sectional hole
will require about 40 percent less rock to be drilled out to make
sufficient room to place the heat exchange tubes, as shown in FIGS.
3a-c. The reduction in the drilled hole size considerably increases
the rate at which the hole can be drilled, possibly decreasing
cost, time on site, and amount of cuttings for disposal. A shaped
hole with an even longer L:W aspect ratio could accommodate several
of the flow tubes in parallel as is shown in FIGS. 3d and 3e. This
allows for drilling half the number of holes in order to obtain a
similar heat transfer capability. This shape maximizes the contact
between the tubes and the rock while reducing the tube to tube heat
exchange. Further, thermal insulation can be placed between the
in-flowing and out-flowing tubes to reduce thermal transfer between
them.
[0041] The shaped, non-circular hole can have any non-circular
cross-section. The non-circular, cross-section holes in accordance
with the embodiments of the present inventions are holes that have
aspect ratios that are larger than one (1.00), where an aspect
ratio is defined as the ratio of a length to a width of the
cross-section shape. So, for example, as defined herein, a circle
has an aspect ratio of one, and an ellipse has an aspect ratio
greater than one since its major axis (length) is larger than its
minor axis (width). In one embodiment, an elliptical cross-section
hole is formed. The elliptical cross-section hole can be formed by
any means, including, but not limited to, a swiveling drill head,
or with a shaped nozzle drilling system, as described below. The
length or angle of throw of the nozzle as it swivels, or the width
of the jet outlet in a shaped nozzle system, determines the overall
width of the elliptical hole. The shaped borehole in accordance
with the embodiments of the present invention is not limited to an
elliptical-shaped hole. Other holes with aspect ratios greater than
1.0 include, but are not limited to, substantially diamond,
slotted, eye-shaped, vesica pisces shaped, egg, dog bone, dumbbell,
rattle, crescent, "C"-shaped, "T"-shaped, "L"-shaped, "I"-shaped,
triangle, square, tetrahedral, rectangular, or parallelogram-shaped
boreholes, or variations thereof, including but not limited to
"pinched" or distorted versions of each, are also considered as
shaped non-circular boreholes within the scope of the present
invention. The cross-section may be symmetric or asymmetric. The
profile may change along the length of the borehole, may include
some circular portions along the length of the borehole, and the
orientation of the non-circular shape may rotate along the length
of the borehole the x, y, or z planes relative to the surface. Such
shaped boreholes may allow for the installation of heat exchange
tubes having an optimum separation between them. From a
thermodynamic perspective, there is an optimum separation between
the tubes. The optimum distance between the tubes is dimensioned to
insure that there is a minimum amount of heat transfer from the
in-coming to the out-going liquid. The tubes can be made of a
rigid, semi-rigid, elastic, or a flexible material.
[0042] In one specific embodiment, an elliptical hole with a
cross-section that is about 2 inches wide by about 5-6 inches long
will enable the placement of in-flow and out-flow tubes which would
have required a 5 inch or 6 inch diameter circular hole. This novel
non-circular cross-section hole will require about 40 percent less
rock to be drilled out to make sufficient room to place the heat
exchange tubes, as shown in FIGS. 3a-c. This reduction in the
drilled hole size considerably increases the rate at which the hole
can be drilled. The hole will also reduce the amount of grout that
needs to be replaced, as well as potentially improve the heat
transfer properties of the hole.
[0043] The shaped or non-circular cross-section holes of FIGS. 3b-c
can be formed in a compositions, materials, soils, rocks or
formations, including but not limited to soil, consolidated soils
and unconsolidated soils, sands, clays, rocks of all geological
types, as well as cements and concretes and the embodiments of the
present invention are not limited to any one material type.
[0044] The shaped or non-circular cross-section holes of FIGS. 3b-c
can be drilled with a number of different technologies, and the
embodiments of the present invention are not limited to any one
exemplary drilling technology. For example, conventional rotary,
hammer, or coiled tubing drilling techniques which produce a
circular hole can be combined with auxiliary processes to produce a
substantially non-circular cross-section. The drilling technologies
may include hard rock or non-contact drilling technologies.
Exemplary and effective technologies for drilling hard rock
efficiently include, but are not limited to, flame jet spallation,
hydrothermal spallation, and water and particle jet techniques,
[0045] The substantially non-circular hole can be formed by a
single process or mechanism, such as, but not limited to,
hydrothermal spallation using a shaped nozzle or nozzles array, or
by rotary drilling using a pulsating cutting tool which can vary in
distance from the center point of the hole in a regular pattern to
produce a non-circular shape, such as that in 8b. Alternatively,
the non-circular hole can be formed by two or more different
processes or mechanisms. In one example, a rotary drill head can
drill a circular hole and an abrasive fluid jet can cut triangular
indentations to produce a shape such as that shown in 8d. The
substantially non-circular bore hole can be formed in one step such
as, but not limited to, air-particle drilling with shaped nozzles,
or multiple steps, such as but not limited to coiled tubing
drilling with a mud motor followed by insertion of a secondary
abrasive milling mechanism with two counter rotating heads driven
by an electric or mud motor to produce a shape such as that in 8c.
The drilling process or processes can occur concurrently at the
bottom of the drilling assembly, such as, but not limited to, a
single pulsating cutting tool, or they may be staggered along the
drilling assembly such that a "primary" drilling process forms the
primary, circular hole while a following "secondary" process higher
up the bottom hole assembly (BHA) shapes the hole into a
non-circular cross-section. Alternatively, the drilling process or
processes can be performed in two separate or independent
operations. As one example, a hole is drilled using rotary bit
drilling; in a secondary process, an erosive or spallation jet is
used to increase the length of the hole without significantly
changing the width. The secondary operation or process can take
place when the drill string from the primary operation or process
is still in place, is being removed, or after the drill string from
the primary operation or process has been completely removed.
[0046] The primary drilling process may include, but is not limited
to, conventional drilling processes such as, but not limited to,
rotary bit, auger, rotary impact, percussion or sonic drilling, or
coiled tubing drilling to form a substantially circular hole. The
secondary process may include contact or non-contact drilling
processes, such as, but not limited to rotary bit, grinding,
milling, abrasion, particle abrasion, spallation, sonication,
scraping, cutting, melting, or fusing or combinations of these
processes. Power to supply the secondary process may be derived
from the rotation of the primary or secondary process drill stem,
hydraulic flow of fluids, including but not limited to water,
circulating fluids, or drilling muds, or from another source, such
as, but not limited to, compressed air flow, or by electrical,
thermal, mechanical, or chemical means.
[0047] The formation of the non-circular hole can include
technologies that use a rotating drill stem, such as, but not
limited to, rotary abrasive drilling or auger drilling through the
use of multiple drill heads, off-set drill heads, pulsed jets,
pulsed cutters, or other mechanisms. There may be one bit or
multiple drill bits, nozzles or drilling surfaces. Bits may be
vertically or horizontally offset from each other. Bits, nozzles,
or drilling surfaces may be oriented vertically, horizontally, or
in other directions. The bits, nozzles or drilling surfaces may be
opposing or counter-rotating. Nozzle or jets may be oriented to
reduce "hold-down" of rock or to aid in cuttings lift and returns.
In addition, there may be secondary or operations to reduce the
size of the cuttings or particles in the return fluids including
grinding, pulverizing, chemical degradation or dissolution, thermal
treatments, or the like.
[0048] The formation of the non-circular hole can include
technologies which do not require a rotating drill stem, such as,
but not limited to, coiled tubing drilling, water jet, air jet, air
spallation, particle impact, hydrothermal spallation, fusion,
laser, chemical, plasma, sonication, or percussion through the use
of multiple or shaped jets, or through the use of a secondary
rotating cutting mechanism in a vertical, horizontal or otherwise
offset position. There may be one drill head or multiple drill
heads or nozzles. Drill heads may be offset from each other or
oriented in different directions.
[0049] In another embodiment, a wellbore milling system that cuts
an existing circular wellbore into the preferred profile can be
used. These drilling techniques can include both drilling
techniques that erode away the rock such as fluid and fluid
particle jets, high temperature spallation flame jet, or hot fluid
or steam drills. In another embodiment, a chemical drill that uses
fluids that are either alkaline or acidic can be used. These jets
of fluids or gases are either directed in the bore hole to create
the non-circular shape, or a shaped nozzle is used to create the
desired hole geometry, as described above. There are also ways to
create non-circular drills using rotating contacting systems with
multiple cutters or by reaming or shaping the hole after drilling
to create the optimum profile. Again, this reaming, or milling,
spalling or other process can occur slightly behind the drilling
head or further up the drill string or in multiple milling tools
placed at different point on the drill string.
[0050] It may be necessary or helpful to determine maximum
principal stress in borehole, the orientation of the BHA, the
orientation of the non-circular borehole, or that orientation of
the BHA or borehole relative to the stresses in the borehole during
the course of creating the borehole. Either can be achieved by
known processes. Information gathered by downhole instrumentation
may be communicated to the surface, in real time or with some
delay, where it is processed and used to guide the drilling
mechanisms in the formation of the borehole shape or orientation.
Alternatively, information gathered by the instrumentation may be
processed by down-hole equipment or "smarts" and fed directly back
to the drilling mechanism, with or without storage or the
additional relay of the information to the surface. Information of
the principal stresses may be gathered by current or future
technologies in advance of drilling, in "real-time," periodically
during the drilling operation with the drilling mechanism is
functioning or stopped, or after the primary drilling has been
completed.
[0051] In order to disclose a method for drilling the novel shaped
or non-circular cross-section boreholes in accordance with the
embodiments of the present invention, one such system (e.g. flame
jet drilling) which is improved to enable the formation of the
novel shaped holes is described below.
Improved Flame Jet Drilling System
[0052] FIG. 4 shows an exemplary schematic diagram of a flame jet
drilling system for shallow shaped holes, in accordance with one
embodiment of the present invention. As used herein a shallow hole
is a hole having a depth that is no more than about 500 feet.
However, the embodiments of the present invention are not limited
to the forming of such shallow holes, and deeper holes can be
drilled via the techniques disclosed herein. Flame jet drilling has
been shown to be most effective when a high velocity, high
temperature combustion stream (e.g., burning hydrogen or
hydrocarbon fuels with air or oxygen) is forced against a rock
surface. The rock may fail by rapid heating and flaking of the
mineral structure, sometimes referred to as "spalling." The rapidly
moving combustion gases strip the "spalls" from the surface
exposing a new surface to be heated, spalled and removed. A flame
jet system in accordance with the embodiments of the present
invention can include the underground components including the
burner head 18 with swivel mechanism 19, centralizers 20, all of
which are connected to the surface through a tube connection system
21 which conveys the oxidant, fuel, supplemental air, coolant, and
water along with the electronic control signals to a coupler 22. At
the surface a rigid frame 23 supports the drill system and a coiled
tube spool 24 holds the nested or bundled tubing which is connected
with the air compressor and fuel source 25. During operation the
burner is continuously fed or translated into the ground at a fixed
rate of penetration. The swivel mechanism 19 oscillates the nozzle
and burner head 18 back and forth using an air pressure drive or
motor driven head to create the elliptical shaped hole.
[0053] Certain details of the drilling head for the system of FIG.
4 are shown in FIGS. 5a-b. FIG. 5a shows a simplified exemplary
diagram of a jet drill head swivel drilling system in accordance
with one embodiment of the present invention for drilling a
non-circular borehole; and FIG. 5b shows an orthogonal
cross-sectional view corresponding to FIG. 5a. As set forth above,
a flame jet burner head is used to create a supersonic combustion
flame burning propane or diesel with compressed air as the oxidant
in its spallation mode of operation. Fuel which can be either
propane or diesel is mixed using a distributor with air which has
been preheated via the cooling of the flame jet chamber. The mixing
of the fuel and air creates a rapid combustion process that creates
a high velocity stream in the combustion chamber. The diameter and
shape of the chamber determines the extent of the combustion as
well as heat transfer to the in-coming air stream. A flame holder
maintains the combustion during the high flow rate conditions.
Further details of the combustion chamber design are described in
references related to flame jet drilling, discussed above. The high
velocity gas stream is forced out through the nozzle 26 where the
gas expands into a supersonic flame 27. Exit velocities of the high
pressure, high temperature combustion product gases in the range of
1.5 to 2 times the speed of sound are typical depending on the
inlet pressure and flow rate of the air and fuel. The rock material
that spalls off the surface 28 moves upward in the air stream where
it is mixed with coolant water 29 or air and transported up the
wellbore annulus 30. The nozzle swivel 31 is a mechanism actuated
by air or electronic means to swivel the jet back and forth over a
predefined arc 32. One or more centralizers 33 are attached to the
drill head 34 and keep the drill head centered in the wellbore as
the nozzle swivels back and forth creating the slot, the elliptical
or the non-circular-shaped hole.
[0054] Alternatively, the elliptical, slot-shaped or non-circular
hole be made by using a water jet or particulate flow system. A
number of water jet designs are already used in rock drilling and
typically include a high pressure pump at the surface with a flow
line down to the small bore nozzle where a very hard material such
as silicon carbide is used to focus the fluid flow into a tight
jet. Particulates can be added to the stream to increase formation
erosion and drilling rates. In some methods a drilling mud is used
for suspending solids and these solids which can be non-metallic or
metallic particles which at high velocities can impact and remove
the rock. A conical jet method has also been described that creates
an erosive cone of fluid that cuts into rock. Such systems can be
modified to include a swiveling mechanism as described above to
enable the formation of the slot, the elliptical or the
non-circular-shaped hole, in accordance with the present invention.
Further details of such jet drilling systems are disclosed in the
references above, which are incorporated by reference herein.
[0055] In accordance with the embodiments of the present invention,
in order to create the non-circular hole design, the drill head may
either be shaped to create the non-circular hole or alternatively
the head is enabled to swivel between to endpoints at a rate and
total movement that is optimized for the drilling process. This
process requires that there be flexibility of the head and the flow
components. For example, a ball type swivel mechanism 31 is shown
in FIG. 5a. The swivel system can be actuated using several
different mechanisms including pneumatic, hydraulic and electrical
actuation. The sweeping process of the swivel also helps remove the
spalled material from the rock face when a flame jet technique is
used.
[0056] As an alternative to the drill head enhanced with a
swiveling mechanism, a shaped jet design for drilling non-circular
or elliptical cross-section holes is shown in FIG. 6a-b. In this
system the non-circular geometry is created by using a slot-forming
shaped or multiple outlet jets that erode away rock using either
flame jet or other water jet drilling methods described above to
create the substantially non-circular and/or elliptical-shaped
hole. A nozzle head using three directed nozzles is shown in FIG.
6a and a projected view thereof is shown in FIG. 6b. The drill head
of FIGS. 6a-b includes the nozzle body 35 and the multiple openings
36 designed to force fluid or hot gases out at an angle from the
drill head, thus creating the elliptical shaped hole. A plurality
of smaller openings can be used is place of each jet with the same
effect to create an elliptical hole when the smaller openings are
oriented in a manner to form the non-circular cross-sectioned
hole.
[0057] Another alternative technique for drilling non-circular
cross-sectional boreholes is shown in FIG. 7a. This system and the
resultant hole it drills are shown in FIGS. 7a-c. As shown in FIG.
7b the system can use particulate flow in a high pressure stream of
either air or fluid such as water or drilling mud to create
overlapping circular bores that form a more or less elliptical bore
hole shape. FIG. 7a shows an overall view of the system while FIG.
7b is a more detailed drawing of the wobbler-nutating section of
the system. The drawing is shown without the cover box installed
which protects the components inside from the fluids, air and
particulates. The system has two reinforced rubber, thermoplastic,
thermoset, or composite flow tubes 37 that provide a mixture of
fluid or air with particulates 39 into the dual nozzles 38 which
are manufactured from a hard material such as tungsten or silicon
carbide. The nozzles 38 have a convergent inlet 41 and a long
straight or slightly divergent outlet section 42 where the mixture
of fluid or air and particles 39 are accelerated to high velocity
and then impacted against the rock surface 51. To create a wobble
motion as is shown in FIG. 7b, the nozzles 38 are connected through
a spherical ball 43 which is attached to a bearing surface 44 that
slides against the inclined surface of the wobble plate 47. The
wobble plate 47 is centered to the main mount plates 42 on the same
axis as the spherical ball 43 using several removable bearing
plates 46. The wobble plate 47 and integral gear assembly is then
rotated by applying a rotary motion using either an air, hydraulic
or electric motor through a belt 48 or by direct drive through a
central hub gear 49 on the motor 40 to the side gears 47 on the
nutating assemblies. The motor is attached to the block using a
motor mount plate 50. The low spots on the two wobbler plates 47
are oriented at 180 out of phase from one another so that the
sideway force of the nozzles counteracts each other helping to keep
the drill assembly centered in the wellbore. The nozzles and tubes
are kept from rotating by fixing the tubes 37 up at a point above
the end of the air motor. The entire assembly is enclosed in a
metal cover box (not shown in the drawing) and the nozzles sealed
using rubber bellows. The resultant hole shape 52 and the
superposition of the heat exchange flow tubes 53 is shown in the
cross section FIG. 7c. The same general concept can work with
rotation of the nozzles instead of wobbling if the outlet holes are
offset from the center or have jets that are directed towards the
sides of the bore as well.
[0058] It should be realized that the shaped boreholes in
accordance with the embodiments of the present invention are not
limited to vertically extending holes. The techniques and systems
in accordance with the embodiments of the present invention can
also be used to form horizontal boreholes. The non-circular
boreholes may also improve the drilling and borehole stability. In
accordance with this aspect of the present invention, the drilling
system can create an elliptical, eye, or slot-shaped hole with the
long direction perpendicular to the principal or maximum stress
direction. In many cases, this maximum stress direction is
vertical, in which can long direction would be in the horizontal
direction. This orientation and geometry is desirable for the
wellbore to survive in the high vertical stresses found especially
in deep subterranean formations by preventing or minimizing
uncontrolled well-bore breakouts or cave-ins. In addition,
increased stability of the borehole can allow the driller to use
lower mud pressures in the borehole possibly increasing the
drilling speed by reducing cuttings "hold-down", creating a more
underbalanced drilling environment, and other issues. The
non-circular hole may also provide conduits for pumping cement in
the annulus between the wellbore and outside of the casing in
traditional or novel cementing and completion operations.
[0059] The optimum shape of the non-circular, slot-shaped or
elliptical hole can be determined by an estimate of the reservoir
stresses present and by applying finite element analysis
techniques. A system to monitor the bit or BHA position relative to
up/down direction in the wellbore can be useful as a part of the
system design. Prior drilling experience in the reservoir can help
determine the best orientation for the non circular borehole shape.
Use of this non-circular approach allows for horizontal bores that
can be left uncased (open hole) for more extended periods of time.
In one embodiment, the formation of such holes requires the use of
a non-contacting flame jet drilling system with a movable nozzle
that swings between pivot points. In a second embodiment, the
non-circular hole can be created by an abrasive fluid or
particle-bearing fluid jet drill that moves between pivot points.
In another embodiment a non-contacting drill can be used that uses
superheated steam or water to drill by means of abrasion, erosion
or spallation. The fluid used in the fluid jet drill can also be
water, drilling mud, or other fluids such as supercritical carbon
dioxide (CO.sub.2) and fluids that erode the rock chemically using
basic or acidic chemicals (such as sodium hydroxide or hydrofluoric
acid in solution). A shaped multiple port nozzle may also be used
to create the non-circular, slot-shaped, or elliptical hole. 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, abrasion, dissolution and or
thermal spalling or in some cases melting of the minerals. In one
aspect, monitoring of the bit position using a remote position
sensor is preferred to control the orientation of the elliptical
hole.
[0060] Horizontal or deviated wellbores have become a major part of
oil and gas production and stimulation processes. In many areas
these horizontal wellbore sections may be hundreds to thousands of
feet in length and may produce oil or gas from a large part of the
horizontal section. Horizontal wells are also being considered for
other applications including production of geothermal fluids. Large
vertical stresses may be present in these environments especially
at great depths. These stresses can cause the wellbore to collapse
where the rocks are of limited strength and/or the pore pressure in
the wellbore drops with through production, drilling, or post
drilling operations. Horizontal drilling has traditionally been
done by rotary drilling either from a coiled tube rig or by
conventional drilling systems. The conventional technologies will
typically drill a more or less circular wellbore in these
horizontal sections. The use of downhole motors and wellbore
tractors allows for extended reach wells where the significantly
horizontal sections can be over 20,000 feet.
[0061] FIG. 8a shows a circular generally horizontal borehole
created during conventional drilling for oil and gas exploration.
The borehole 54 is typically subjected to high principal stresses
in the primarily vertical direction shown by the arrows 55.
Breakouts 56 caused by rock failure are shown as the scooped out
regions (e.g., lobes) in the horizontal direction relative to the
original circular borehole shape 57. Tensional fractures 58 created
during drilling can also be found parallel to the direction of the
maximum principal stress 55. FIG. 8b shows the same circular
borehole 54 extended into a more elliptical shape by two lobes 59
created by a secondary drilling process, as described previously.
An alternate version of the generally elliptical shape is shown in
FIG. 8c where the shaped regions 60 are more pronounced and look
much like the breakout themselves. The secondary drilling process
removes the rock materials that would eventually collapse into the
borehole when the drill is removed from the borehole. As a bonus
effect, by strengthening the borehole in this manner the driller
may be able to use lower mud pressures during drilling and which
can lead to increases in the drilling rates. Reaming the entire
borehole to a larger circular shape as is commonly done will only
lead to breakouts again because the circular geometry in not
inherently stable under these stress conditions. FIG. 8d shows the
borehole 54 extended to include regions 61 that have a more
pronounced shape that can be a stable hole geometry. FIGS. 8b-d
show in general the shapes of boreholes that can be possible for
achieving a more stable borehole.
[0062] In addition to the so-called non-contact techniques for
forming shaped boreholes described above, shaped boreholes in
accordance with the embodiments of the present invention may also
be formed using conventional systems that have been modified to
enable the formation of the novel shaped boreholes of the present
invention. Using these conventional drilling technologies, a way
for creating a shaped borehole (e.g., elliptical shape, oval, eye,
or slot-shaped) involves using multiple heads that rotate and that
are driven individually. Such multiple head bits can be configured
to form the shaped boreholes in accordance with the embodiments of
the present invention. Exemplary geometries for such multiple head
bits are shown in U.S. Pat. No. 4,185,703, which discloses an
apparatus for producing deep boreholes, the disclosure of which is
herein incorporated by reference.
[0063] In summary, drilling non-circular boreholes has the
advantage of improving the efficiency of the drilling and/or
completion operation, providing a wellbore with a shape more
optimized for the application, and may produce holes that are
inherently more stable and resistant to collapse or break-out.
These non-circular holes through the use of traditional contact
drilling technologies complimented by a secondary operation. In
addition, non-contact drilling systems may be even better suited
for the task of combination of higher drill rates possible with the
spallation or non-contacting systems and the reduced area of
cutting provided by the non-circular, shaped, elliptical, or
slot-shaped hole concept in accordance with the embodiments of the
present invention enable extremely fast drilling rates to be
obtained. Drilling a non-circular hole may be more economic in
applications such as, but not limited to, GHP's where the
non-circular hole requires less time to drill and less grout to
secure the heat transfer tube in place for an equivalent outer
diameter hole. This shape may also have more optimized heat
transfer properties compared to a circular bore. These will
dramatically affect the economics of certain drilling projects and
make them more feasible in many areas around the world.
[0064] Several embodiments of the present invention have several
advantages over prior art methods and systems by being inherently
more suitable for forming a non-circular hole. For example, using a
swiveling or a shaped jet drilling head, the present system is able
to form non-circular cross-sectioned bore holes by using a non
contacting drill mechanism. Such holes can be drilled to much
greater depths at much faster rates and at a reduced rate of
material excavation, leading to significant cost savings. This may
also produce boreholes which are inherently more stable, thereby
reducing the time and expense of uncontrolled break-out. The
non-circular shape may also allow for certain wellbores to be left
unsupported or uncased for longer periods of time, including
indefinitely.
[0065] The applications for such non-circular shaped boreholes may
include geothermal power generation, such as enhanced geothermal
systems (herein referred to as EGS) and hot dry rock (herein
referred to as HDR), or applications where the bore hole will be
left unsupported for extended periods (minutes, hours, or days),
such as in oil and gas exploration and production (herein referred
to as oil and gas E&P) operations, or in situations where the
wellbore will be left unsupported indefinitely, such as in an
uncased wellbore. An uncased wellbore may have an inner surface
that comprises the formation, or one that is substantially
comprised of fused rock, ice, a layer of a non-metallic material,
such as a thermoplastic, thermoset, composite or ceramic, or a
layer of fused metallic material. In addition to EGS-HDR and oil
and gas E&P, other conventional applications could benefit by
the drilling of non-circular boreholes with reduced tendency
towards break-out, including, but not limited to, water well
drilling, trenchless pipe installation, sewer and municipal system
construction, resource mining, chemical disposal wells, CO.sub.2 or
nuclear storage wells, downhole chemical reactions (such as, but
not limited to, municipal waste oxidation or biofermentation),
bores in ice, or wells for scientific or geologic study, including
test holes or secondary holes used for measurements in the above or
other operations and applications.
[0066] All patents, patent applications, publications, and
descriptions mentioned above are herein incorporated by reference.
None is admitted to be prior art.
[0067] As will be understood by those skilled in the art, other
equivalent or alternative systems and methods for forming shaped
boreholes according to the embodiments of the present invention can
be envisioned without departing from the essential characteristics
thereof. Accordingly, the foregoing disclosure is intended to be
illustrative, but not limiting, of the scope of the invention which
is set forth in the following claims.
* * * * *