U.S. patent application number 12/103480 was filed with the patent office on 2008-10-23 for flexible drill shaft.
This patent application is currently assigned to Schlumberger Technology Corporation. Invention is credited to Dominique Sabina, Jose Teixeira.
Application Number | 20080257606 12/103480 |
Document ID | / |
Family ID | 38460603 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080257606 |
Kind Code |
A1 |
Teixeira; Jose ; et
al. |
October 23, 2008 |
Flexible Drill Shaft
Abstract
A flexible drill shaft for drilling lateral boreholes
comprising: a helical outer wire coil spring; and at least one
inner helical wire coil spring residing concentrically within the
outer coil spring, with the coils of adjacent springs having an
opposite pitch; wherein the wire forming each helical spring has a
cross section such that when the drill shaft is in a straight
alignment there is planar contact between adjacent coils of the
spring.
Inventors: |
Teixeira; Jose; (Chaville,
FR) ; Sabina; Dominique; (Montrouge, FR) |
Correspondence
Address: |
SCHLUMBERGER OILFIELD SERVICES
200 GILLINGHAM LANE, MD 200-9
SUGAR LAND
TX
77478
US
|
Assignee: |
Schlumberger Technology
Corporation
Sugar Land
TX
|
Family ID: |
38460603 |
Appl. No.: |
12/103480 |
Filed: |
April 15, 2008 |
Current U.S.
Class: |
175/74 ;
72/135 |
Current CPC
Class: |
E21B 7/06 20130101; E21B
17/20 20130101; E21B 17/22 20130101 |
Class at
Publication: |
175/74 ;
72/135 |
International
Class: |
E21B 7/08 20060101
E21B007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2007 |
EP |
07106674.0 |
Claims
1. A flexible drill shaft for drilling lateral boreholes
comprising: a helical outer wire coil spring; and at least one
inner helical wire coil spring residing concentrically within the
outer coil spring, with the coils of adjacent springs having an
opposite pitch; wherein the wire forming each helical spring has a
cross section such that when the drill shaft is in a straight
alignment there is planar contact between adjacent coils of the
spring.
2. A flexible drill shaft according to claim 1 wherein the cross
section of the wire is square, rectangular or lozenge.
3. A flexible drill shaft according claim 1 wherein there are
ridges on the contact surface of the coils.
4. A flexible drill shaft according to claim 1 wherein there are
grooves on the contact surface of the coils.
5. A flexible drill shaft according to claim 1 wherein the coil
springs are formed from at least two wires coiled in parallel.
6. A flexible drill shaft according to claim 1 wherein the coil
springs have a preload.
7. A flexible drill shaft according to claim 1 comprising a torque
spike filter.
8. A drilling apparatus comprising the drill shaft according to
claim 1 and a drill bit attached to the lower end of the shaft.
9. A method of making a flexible drill shaft according to claim 1
comprising: winding wire to form a helical coil spring; applying a
mechanical deformation to the wire as it is being wound; and using
the helical coil spring to form a flexible drill shaft; wherein the
mechanical deformation applied results in the wire after being
wound having a cross section such that when an axial load is
applied to the drill shaft there is planar contact between adjacent
coils of the spring.
10. A method of making a flexible drill shaft according to claim 9
comprising: applying a preload as the wire is being wound.
11. A method according to claim 9 comprising using dimensional or
thermal expansion to tightly assemble two or more coil springs.
Description
TECHNICAL FIELD
[0001] This invention relates to flexible drill shafts and in
particular flexible drill shafts able to transmit a high torque
during drilling of lateral boreholes.
BACKGROUND ART
[0002] In oil and gas wells, it is often desirable to drill holes
laterally out from a main vertical borehole to increase the
communication with the formation surrounding the main borehole and
the drainage area. These lateral holes are generally known as
drainholes. They provide a passageway through the surrounding
formation and can increase the flow rate of the hydrocarbons into
the well casing of the main borehole and improve the amount of
hydrocarbon extracted.
[0003] In order to have drainholes having a significant length, the
equipment or apparatus used to drill the drainholes generally have
a flexible shaft to have the ability to change the direction of the
apparatus from the main borehole and the lateral borehole and to
transmit the rotational power and the rate of penetration to the
drill bit.
[0004] U.S. Pat. No. 6,220,372 discloses an apparatus for drilling
lateral drainholes comprising a flexible shaft formed from at least
two helically wound coil springs. The document discloses that the
springs should be formed from wire having a circular cross
section.
[0005] U.S. Pat. No. 4,658,916 discloses a flexible drill shaft
formed from at least two helically wound coil springs formed from
wires having rectangular cross section. This document describes
that the wire used to form the coils springs has a rectangular
cross section. However if a coiled spring is formed from
rectangular cross sectional wire, during the winding process the
wire can be distorted due to the pressures altering the final cross
section shape of the wire that is forming the spring, such that is
no longer rectangular, as shown in FIG. 1.
[0006] One of the difficulties of having a flexible shaft is that
while the flexibility allows it curve to direct the drill bit at an
angle away from the main borehole to drill a drainhole and
therefore help the drilling apparatus negotiate the bend in the
bore hole so that it can drill in a path at an angle away from the
main borehole. The flexibility of the shaft can reduce stability of
the shaft when it is required to drill in a straight path and can
reduce the torque that is provided to the drill bit.
[0007] Therefore it is an object of the invention to provide a
flexible shaft with planar contact between coils of the springs,
for stably transmitting torque and axial load in a straight guide
path or in a curved guide path, to a drill bit.
DISCLOSURE OF THE INVENTION
[0008] One aspect of the invention comprises a flexible drill shaft
for drilling lateral boreholes comprising: a helical outer wire
coil spring; and at least one inner helical wire coil spring
residing concentrically within the outer coil spring, with the
coils of adjacent springs having an opposite pitch; wherein the
wire forming each helical coil springs has a cross section such
that when the drill shaft is in a straight alignment there is
planar contact between the wire of adjacent coils of the spring.
There is planar contact between the adjacent coils when a
rotational force and an axial load are applied to the drill shaft
during drilling in a straight pathway. Having planar contact
between the coils forming each coiled spring helps prevent buckling
of the drill shaft. The cross section of the wires is such that
planar contact between adjacent coils is maintained even when the
drill shaft is drilling in a straight direction.
[0009] Preferably the cross section of the wire is prismatic. More
preferably the cross section of the wire of the flexible drill
shaft is square, rectangular or lozenge. These cross section shapes
allows for planar contact between the adjacent coils of a coil
spring.
[0010] The coils of coiled spring can have ridges on the contact
surface of the coils and/or grooves on the contact surface on the
coils. Having ridges and/or grooves increases the friction ratio
between the coils of each coiled spring.
[0011] The coiled springs can be formed from at least two wires
coiled in parallel. Having two or more wires coiled in parallel
allows more torque to be transmitted and reduces the coiling
angle.
[0012] A flexible drill shaft can be formed from coil springs
having a preload. Having a preload between spires gives the springs
a longitudinal stiffness which helps provide the shaft with
stability during drilling in a straight trajectory.
[0013] The flexible drill shaft can further comprise a torque spike
filter. This protects the shaft from damage caused by a torque
spike. The filter can be placed at any place along the shaft.
[0014] The flexible drill shaft can further comprise a drill bit at
the lower end of the shaft.
[0015] A another aspect of the invention comprises a method of
making a flexible drill shaft as described above comprising:
winding wire to form a helical coil spring; applying a mechanical
deformation to the wire as it is being wound; and using the helical
coil spring to form a flexible drill shaft; wherein the mechanical
deformation applied results in the wire after being wound having a
cross section such that when an axial load is applied to the drill
shaft there is planar contact between adjacent coils of the
spring.
[0016] Preferably the method comprises applying a preload to the
wire as it is being wound.
[0017] The method can comprise using dimensional or thermal
expansion to tightly assemble two or more coil springs together.
This can help reduce the gap between coil springs of the flexible
drill shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a schematic view of the deformation of wire
after winding;
[0019] FIG. 2 shows a schematic view of the wire before and after
the winding process;
[0020] FIG. 3 shows a schematic view of one wire cross section for
use in making a coiled spring of the invention;
[0021] FIG. 4 shows a schematic view of one of the coiled spring
that can be used for the invention; and
[0022] FIG. 5 shows the forces taking place on a coiled spring.
MODE(S) FOR CARRYING OUT THE INVENTION
[0023] The flexible shaft is formed of a helically wound outer coil
spring and one or more helically wound and smaller inner coils
springs residing concentrically therein. Each successively smaller
inner coil spring has an outer diameter substantially the same as
the inner diameter of the adjacent larger coil spring. Each coil
spring is wound in the opposite direction to that of the adjacent
coil springs, the outer coil spring sets the winding reference
direction, and is wound in the same direction as the direction that
the drill bit will rotate. The springs are held rigid in relation
to each of the other coil springs at the drill shafts upper and
lower ends. The springs are close wound with axially adjacent coils
of each coil spring in contact with each other. During assembly
dimensional or thermal expansion can be used to remove any gaps
between adjacent coil springs, so that the coil springs are
assembled tightly together.
[0024] Each of the springs is formed of wound wire, having a
geometric cross section. However the winding process can cause the
initial cross section of the wire to deform as it is being coiled
to form a spring. Therefore the wire forming the spring has a
different final cross section, once formed into the spring than
what it initially starts off with before it is coiled.
[0025] For example, as shown in FIG. 1, a wire with an initial
square cross section is deformed into a wire having a trapezium
cross section due to the compression forces placed on the wire as
it is being formed into the coil spring. A coil spring that is
formed from wire having a trapezium cross section along its length,
as in FIG. 1, does not have planar contact between adjacent coils
of the spring.
[0026] To form a coiled spring with planar contact between adjacent
coils the initial cross section of the wire before winding has to
be corrected in order to take into account the deformation that
occurs during the winding process. With reference to FIG. 2, a wire
having an initial trapezium cross section when used to form a
coiled spring the final shape of the cross section of the wire once
formed into the spring is a square due to the compression forces
placed on the wire during the winding process. The angle, .beta.,
is the angle by which the cross section of the wire is corrected by
to compensate for the deformation that the wire will under go
during the winding process to form the spring. The final square
cross section allows for planar connect between the adjacent coils.
With planar contact between the coils of the spring, the flexible
drill shaft is able to have improved transmittal of torque and
axial load to an out put device such as a drill bit, when the drill
shaft is in a curved and straight form.
[0027] The angle correction to the initial wire used for forming
the spring can be done by either applying an opposite mechanical
deformation to the wire during the winding process, or by directly
wire drawing with a cross section that when altered due to the
compression forces applied during the winding process will result
in a final cross section that allows planar connect between
coils.
[0028] Having planar contact between the coils improves the
performance of the flexible shaft when drilling in a straight path.
Planar contact between the adjacent coils gives the shaft a better
anti- buckling effect and ensures rigidity of the shaft, when
placed under an axial load, such as during drilling.
[0029] Planar contact between the surfaces of coils increases the
friction this reduces the shrinking of the diameter of the spring
under torque. Reducing the shrinking of the diameter of the spring
under torque can also be helped by having a spring with a lozenge
cross section. When the wire has a lozenge section as indicated in
FIG. 3, there will be planar connect between adjacent coils. Wire
having a lozenge cross section to be used to form a coiled spring
will have an angle .alpha., where angle .alpha. is equal to the
corrected angle .beta., to take into account deformation that
occurs due winding process, and an additional angle such that the
wire maintains a lozenge cross section after the winding
process.
[0030] When the spring coils forming the flexible drill shaft are
subjected to torque this can cause either a decrease in the
diameter with a corresponding increase in length or an increase in
diameter with a corresponding decrease in length. Having alternate
winding of the springs forming the shaft, when the springs are
placed under torque one spring expands in diameter and its adjacent
spring decreases in diameter thereby creating a strong, stable and
flexible shaft.
[0031] The springs used to form the flexible shaft can be preloaded
springs. A preload is applied during the winding process of the
spring. This gives the drill shaft a lengthwise stiffness allowing
the shaft to have stability when drilling in a straight
direction.
[0032] With reference to FIG. 4, to increase the friction ratio of
the contact between adjacent coils 1, ridges 2 and/or grooves 3 are
added to the wire forming the coils. Processes for forming the
ridges and grooves on the wire can include mechanical deformation
of the formed wire or directly wiredrawing, however other methods
may be used. Increasing the friction ratio between adjacent coils,
will reduce the slippage that can occur between the adjacent
surfaces, and therefore improve the stability of the drill
shaft.
[0033] In operation, a drilling apparatus comprising the flexible
drill shaft according to the invention with a drill bit attached to
the lower end of the shaft is lowered down into the wellbore. To
drill drainholes, the flexible shaft is guided so as to turn and
direct the drill bit to drill laterally into the side of the main
borehole. The flexibility of the shaft enables the shaft to turn in
a short radius. A rotary motor enables rotation of the shaft and
the drill bit. Rotation is imparted by a motor and axial load is
transmitted through to the flexible drill shaft causing the drill
bit to rotate and drilling to proceed. A rotating torque and an
axial force are applied to the drill bit through the flexible drill
shaft.
[0034] With reference to FIG. 5, with the flexible drill shaft
having planar contact between adjacent coils of the spring, the
applied torque and axial force is more effective in the drilling
process. The torque transmitted to the drill bit is improved. The
transmissible torque is the sum of the rotational torque 4 and
clutch effect which is due to the combination of the axial force 5
down the length of the shaft and the friction ratio between the
contact surfaces of adjacent coils.
[0035] Further changes can be made without departing from the scope
of the invention.
* * * * *