U.S. patent application number 11/680602 was filed with the patent office on 2008-08-28 for well wall gripping element.
Invention is credited to Falk W. Doering, Wade D. Dupree.
Application Number | 20080202769 11/680602 |
Document ID | / |
Family ID | 39714585 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080202769 |
Kind Code |
A1 |
Dupree; Wade D. ; et
al. |
August 28, 2008 |
Well Wall Gripping Element
Abstract
A gripping element for incorporation into a track of a downhole
tractor. The gripping element may be configured with an arcuate or
curved surface in order to roughly match the arcuate nature of a
well through which the downhole tractor is advanced. Due to the
matching arcuate surfaces of the gripping element and the wall of
the well, problems associated with uneven wear on the tracks may be
avoided. Furthermore, damage to the well wall may be minimized as a
result of the substantially matching surfaces of the well wall and
the track made up of such gripping elements. Additionally, the
gripping element may be made up of primarily a monolithic body in
order to avoid challenges presented by some segmented body
configurations.
Inventors: |
Dupree; Wade D.; (Sugar
Land, TX) ; Doering; Falk W.; (Houston, TX) |
Correspondence
Address: |
SCHLUMBERGER IPC;ATTN: David Cate
555 INDUSTRIAL BOULEVARD, MD-21
SUGAR LAND
TX
77478
US
|
Family ID: |
39714585 |
Appl. No.: |
11/680602 |
Filed: |
February 28, 2007 |
Current U.S.
Class: |
166/382 ;
175/230 |
Current CPC
Class: |
E21B 4/18 20130101; E21B
23/14 20130101; E21B 23/001 20200501 |
Class at
Publication: |
166/382 ;
175/230 |
International
Class: |
E21B 23/00 20060101
E21B023/00 |
Claims
1. A driving mechanism for interfacing a well wall with a gripping
element, said gripping element having an arcuate surface selected
based on an arcuate character of the well wall, wherein an
interfacing of the gripping element with the well wall causes the
driving mechanism to move relative to the well wall.
2. The driving mechanism of claim 1 wherein said gripping element
comprises at least one tooth at said arcuate surface for the
interfacing.
3. The driving mechanism of claim 1 wherein said gripping element
comprises a body that is one of a monolithic and a segmented
variety.
4. The driving mechanism of claim 3 further comprising: a rotable
pin through said body; and rollers secured at ends of said rotable
pin.
5. The driving mechanism of claim 1 wherein said gripping element
is of a y-shaped configuration comprising a male region and a
female region.
6. The driving mechanism of claim 5 wherein each said region
further comprises more than one tooth at a surface thereof.
7. The driving mechanism of claim 1, wherein the driving mechanism
is a downhole tractor and said gripping element forms a portion of
a track on the downhole tractor.
8. The driving mechanism of claim 7 wherein said track is a first
track, the downhole tractor further comprising between about 1 and
about 3 additional tracks.
9. The driving mechanism of claim 7 wherein said downhole tractor
further comprises a central housing comprising: an expansion
mechanism for engaging said track with the well wall.
10. The driving mechanism of claim 9 further comprising an
extension coupled to said central housing for accommodating a
downhole tool.
11. A downhole tractor for use within a well and comprising a
gripping element having a monolithic body with an arcuate surface
configured based on an arcuate character of a wall of the well, the
downhole tractor to effect an interface between the arcuate surface
and the wall, which causes the downhole tractor to move relative to
the well wall.
12. The downhole tractor of claim 11 wherein the arcuate surface is
substantially continuous across a width of the gripping
element.
13. The downhole tractor of claim 11 wherein the arcuate surface is
configured to contact the wall through between about 50% and about
97% of the interface.
14. A gripping element for use on a track of a downhole tractor,
the gripping element comprising an arcuate surface to interface a
well wall, said arcuate surface substantially matching an arcuate
shape of the well wall.
15. The gripping element of claim 14 wherein said arcuate surface
displays a radius that is within about one inch of a radius of the
well wall.
16. The gripping element of claim 14, wherein the arcuate shape of
the well wall is in the form of a diameter, said diameter chosen
from the group consisting of about 6.5 inches, about 8.5 inches and
about 10.5 inches, and wherein said arcuate surface of the gripping
element is in the form or a radius, said radius chosen from the
group consisting of about 3.25 inches, about 4.25 inches and about
5.25 inches.
17. A downhole tractor comprising: a chain for engaging a well wall
and rotating thereagainst to propel the downhole tractor with
respect to the well wall, wherein the chain comprises: a plurality
of links, wherein each link comprises at least one tooth formed in
an arcuate shape selected based on an arcuate character of the well
wall.
18. The downhole tractor of claim 17, wherein the plurality of
links contains interconnecting links such that a width of the chain
contains no more than two interfacing junctions between connected
links.
Description
FIELD OF THE INVENTION
[0001] Embodiments described relate to downhole tractors for use in
the oilfield industry. A variety of downhole tractor components are
discussed. In particular, embodiments of gripping element links for
tracks of a downhole tractor are described in detail.
BACKGROUND OF THE RELATED ART
[0002] Driving mechanisms in the oilfield industry, such as
downhole tractors, may be employed in conjunction with the
completion and operation of hydrocarbon wells. For example,
downhole tractors may be used to convey equipment such as logging
tools for gathering and recording geologic information relative to
the well, ultimately optimizing its productivity. Delivering a tool
with a driving mechanism in this manner may be particularly
beneficial where the well is highly deviated or horizontal. This is
because a downhole tractor may be adept at driving a tool through
more non-vertical or tortuous well configurations where the option
of dropping the tool down vertically is unavailable.
[0003] The above described downhole tractor may operate by way of
rotatable tracks configured to contact the wall of the well and
rotate thereagainst to advance the downhole tractor with respect
thereto. For example, the downhole tractor may be equipped with a
centralized housing coupled to tracks interfacing opposite sides of
the well wall. The tracks may be made up of a plurality of links
similar to a chain. Like a conventional farm tractor, or tank, the
tracks may then be rotated with the links pressed against the well
wall to achieve advancement of the tractor driving mechanism within
the hole. In this manner, an instrument that is attached to the
tractor, such as the above-noted logging tool, may be conveyed
within the well.
[0004] The above-described links are generally between about 1 and
4 cm in width and made up multiple plates (for example, see plates
359 and 360 of FIG. 3). The plates themselves may be of stainless
steel or other durable material and less than about 4 mm thick.
Limiting the thickness of the plates in this manner allows the
plates to be formed by fairly inexpensive conventional stamping
techniques. Nevertheless, between about 4 and 10 plates may be
stacked across a given link in order to provide the indicated 1 to
4 cm link width.
[0005] Unfortunately, while the downhole tractor may be adept at
driving a tool through a variety of well configurations, the links
of the tracks are fairly susceptible to wear and breakdown. In
addition to the limited thickness of the plates, the teeth of the
plates (see again FIG. 3, teeth 310) are aligned and form a
substantially straight line across the link width. This straight
line arrangement of the teeth causes the plates to wear unevenly
over a period of use. This is due to the circumferential nature of
the well wall. When the straight line arranged teeth attempt to
contact the arcuate well, only the plates at the outer edges of the
links contact the well wall (for example at locations 315), thus
causing these plates to wear at a greater rate than those at a more
longitudinally central location of the links. As a result these
plates are susceptible to fracture sooner than the remainder of the
plates.
[0006] In addition, this prior art link provides inefficient
traction against the well wall due to the large area across the
link's width that does not touch the well wall. This remains true
until either the teeth 310 of the outermost plates 359 dig into and
damage the well wall; or the teeth 310 of the outermost plates 359
wear down to the point the next outermost plates touch the well
wall (i.e. the plates 360 immediately adjacent to the outermost
plates 359).
[0007] The rate or degree of this wear or wear into the well wall
itself may be a factor of the amount of load that is being conveyed
by the downhole tractor. This load is substantially determinative
of the amount of force being applied to the interface of the tracks
and the well wall. Given that the downhole tractor is configured to
drive relatively large loads such as logging tools, the degree of
wear is likely to be quite significant. Thus, as a track rotatably
advances across the surface of the well wall uneven contact
therebetween may eventually result in track wear and/or failure,
and damage to the well wall.
[0008] A considerable amount of cost in terms of downtime and
equipment repair may be associated with a track failure as noted
above during operation. Furthermore, even in advance of complete
track failure, uneven wear of the track and its links results in an
inherent inefficiency of operation for the downhole tractor. For
example, even in advance of complete track failure, the track may
be left with outer edges that are ineffective for the purpose of
tractor advancement within the borehole. Wearing of this nature may
result in the inefficiency of decreased gripping ability of the
track perhaps even leading to its slippage. This in turn may also
result in added damage to the well wall.
[0009] As opposed to uneven wear on the track as described above,
wear may be directed at the well wall due to its circumferential
nature. This may be of even greater concern than track wear in
circumstances where the downhole tractor is intended to encounter
open well configurations. That is, the downhole tractor may be
required to come into direct contact with the soil formation. Thus,
the downhole tractor may traverse a variety of soil consistencies,
including soft, more easily degradable portions of the well wall.
Uneven application of force at the edges of the links in such well
areas may lead to dig in and shearing damage to the well wall.
Unlike damage to the track, well wall damage at a location
potentially thousands of feet from the surface may not be repaired
by mere removal of the downhole tractor and replacement of its
track.
SUMMARY
[0010] A driving mechanism for interfacing a well wall is provided.
The mechanism includes a gripping element for contacting the well
wall wherein the element is configured with an arcuate surface
selected based on an arcuate character of the well wall.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a side view of a downhole tractor employing an
embodiment of a gripping element having an arcuate surface and
disposed within a well.
[0012] FIG. 2 is a cross-sectional view of the gripping element of
the downhole tractor of FIG. 1 shown in contact with a well
wall.
[0013] FIG. 3 is a cross-sectional view of a prior art embodiment
of a gripping element of a downhole tractor within the well of FIG.
1.
[0014] FIG. 4 is a cross-sectional view of a gripping element
according to another embodiment of the invention.
[0015] FIG. 5 is a perspective view of one embodiment of gripping
element according to the present invention.
[0016] FIG. 6 is a top view of a plurality of the gripping elements
of FIG. 5 connected to form a track.
[0017] FIGS. 7 and 8 are gripping elements according to alternative
embodiments of the present invention.
DETAILED DESCRIPTION
[0018] Embodiments are described with reference to certain gripping
element links for tracks of a downhole tractor. Focus is drawn to
gripping element links having a monolithic or integrally formed
body. However, a variety of gripping element link configurations
may be employed. Regardless, embodiments described herein include
gripping element links having an arcuate surface selected based on
an arcuate character displayed by the surface of a well wall.
[0019] Referring now to FIG. 1, an embodiment of a driving
mechanism in the form of a downhole tractor 101 is shown within a
well 197 of substantially horizontal or deviated configuration. In
the embodiment shown, the well 197 is of an open configuration such
that tracks 175 of the downhole tractor 101 may be in direct
contact with the geologic formation 199 surrounding the well 197.
However, in other embodiments, the downhole tractor 101 may be
driven through a borehole casing lining a closed well.
[0020] The downhole tractor 101 of FIG. 1 may be advanced through
the well 197 by way of the noted tracks 175, which rotate against a
wall 195 of the well 197 in order to convey logging tools and other
devices which are attached to the tractor 101 through the well 197.
In the embodiment of FIG. 1, tracks 175 are shown to one side of a
central housing 125 from which they may be deployed. However,
anywhere from about 1 to about 4 tracks 175 (or even more if
desired) may be disposed on various embodiments of the downhole
tractor 101. A logging tool or another appropriate tool may be
coupled to an end of the central housing 125 and conveyed through
the well 197 by operation of the downhole tractor 101.
[0021] The above-noted central housing 125 may be equipped with an
expansion mechanism such as opening arms 150, which expand the
tracks 175 into engagement with the well wall 195 to allow for the
tracks 175 to rotate thereagainst to propel the tractor 101.
Alternatively the opening arms 150 may be moved inwardly toward the
central housing 125 to disengage the tracks 175 from the well wall
195. A wide variety of such conventional expansion mechanism
configurations and other actuators may be available for the
deployment and retraction of the tracks 175.
[0022] Regardless of the particular expansion or retraction
mechanisms employed, the downhole tractor 101 may be configured to
traverse an irregularly shaped well. For example, in the case of an
open well 197 of less than consistent diameter, the expansion
mechanism and retraction mechanisms may work in concert by
conventional means to ensure a substantially consistent force for
engagement of the track 175 against the well wall 195 throughout a
downhole tractor 101 conveyance operation.
[0023] A downhole tractor 101 such as that of FIG. 1 may be adept
at traversing horizontal or highly deviated wells as a result of
the provided tracks 175. As shown in FIG. 1, in a deployed state,
the tracks 175 extend from the central housing 125 and travel in a
belt-like manner adjacent the well wall 195. Additional arms or
other mechanisms (not shown) may be employed to ensure consistent
contact of a track 175 against the well wall 195.
[0024] Additionally, a gear box may be contained within the central
housing 125 for transferring power to drive sprockets (not shown)
and rotating the tracks 175 by conventional means. The tracks 175
may also be driven by a rotable screw or other means. Regardless of
the particular driving technique employed, the tracks 175 are adept
at conforming to and gripping the well wall 195, open or otherwise.
Thus, the downhole tractor 101 may be effectively driven through
the well 197 by rotation of the tracks 175 as described.
[0025] In one embodiment, the above described tracks 175 are made
up of a plurality of gripping elements or links 100. Each of these
gripping elements 100 is provided with teeth 110 for contacting and
gripping the well wall 195. As detailed with reference to FIGS. 2
and 3, the gripping elements 100 of FIG. 1 are configured with an
arcuate surface 201 displaying a radius that may be configured
based on the diameter of the well 197 itself. Thus, unlike prior
art gripping elements 300 of a conventional downhole tractor, the
gripping elements 100 of FIG. 1 are particularly configured to
minimize wear on the well wall 195, as well as the tracks 175
themselves, and to increase the area of contact between the
gripping element teeth 110 and the well wall 195 across the width
of the gripping element 100 as the downhole tractor 101 is driven
through the well 197.
[0026] This minimization of wear on the well wall 195 and tracks
175 is attained in a manner that avoids compromise of the gripping
character of the gripping elements 100. For example, as detailed
further below, the gripping elements 100 are able to maintain teeth
110 of sufficient sharpness and durable character for proper
advancement of the downhole tractor 101 during operation.
Nevertheless, in spite of the retained characteristics of the teeth
110, the likelihood of uneven wearing on the tracks 175 or
degradation of the well wall 195 is minimized due to the arcuate
surface 201 of the gripping elements 100 (see FIG. 2).
[0027] Continuing now with reference to FIG. 2, a cross-sectional
view of one of the above described gripping elements 100 is shown
in contact with a well wall 195. This depiction reveals a
cross-section of the gripping element 100 having a monolithic or
integrally formed body 200 which contacts the well wall 195 with
its arcuate surface 201. In one embodiment, this arcuate surface
201 is at the apex of the tooth 110 of the gripping element 100.
The monolithic body 200 may be of a conventional ceramic, composite
material or metal of suitable durability.
[0028] As shown in FIG. 2, the monolithic body 200 terminates at a
tooth 110 of the gripping element 100 which is configured for
gripping the well wall 195 at an interface 275 thereof. Also
apparent in FIG. 2 is the substantially continuous nature of the
arcuate surface 201 of the tooth 110 and the manner in which it
appears to match the arcuate character displayed by the well wall
195. As alluded to above, the arcuate surface 201 of the gripping
element 100 substantially reduces the amount of wear on the element
100 as well as on the well wall 195.
[0029] Continuing with reference to FIGS. 2 and 3, the gripping
element 100 of the embodiments described herein is depicted in
contrast to a prior art gripping element 300. As shown, each
gripping element 200, 300 includes pins 250, 350 securing rollers
225, 325 through the body of the element 200, 300. However, as
indicated above, the monolithic body 200 of the gripping element
200 of FIG. 2 includes an arcuate surface 201 for contacting a well
wall, whereas the plates across the width of the prior art gripping
element 300 have teeth 310 that are arranged in a straight line.
The results of this distinction may be significant as detailed
below.
[0030] Unlike the substantially matching and smooth interface 275
between the arcuate surface 201 and the well wall 195 as shown in
FIG. 2, the prior art gripping element 300 is made up of side 359
and interior 360 plates that leave the corners 315 of a flat
surface to contact the well wall 195 (see FIG. 3). Thus, a prior
art interface 375 includes a large area of non-contact between the
well wall 195 and the prior art gripping element 300. As a result,
the force that the prior art gripping element 300 applies to the
well wall 195 is directed exclusively through the noted corners
315. Therefore, wear on the prior art gripping element 300 is
focused disproportionately to the side plates 359 as the gripping
element 300 pulls a load through the well 197. Thus causing a
tremendous amount of stress at areas 390 of the well wall 195.
[0031] The above-noted disproportionate application of force
through the side plates 359 of the prior art gripping element 300
may result in deterioration of the side plates 359, the degree and
rate of which may be dependent upon factors such as the amount of
load pulled by the gripping element 300 as well as the durability
of the side plates 359. Regardless, the prior art gripping element
300 is prone to more rapid and extensive deterioration as compared
to the gripping element 100 of embodiments employing an arcuate
surface 201 as described herein. Thus, tracks employing such prior
art gripping elements 300 may more readily become inefficient and
ultimately more prone to failure.
[0032] In addition to wear at the edges of the prior art gripping
element 300, the well wall 195 itself is susceptible to wear and
damage by these edges (i.e. the side plates 359). This may be of
particular concern in the case of an open well 197 as shown in
FIGS. 1-3, where the well wall 195 includes bare and potentially
soft geologic formation 199 prone to damage by application of such
localized forces. This can be seen in FIG. 3 where the damaged
locations 390 of the formation 199 have resulted from the
disproportionate amount of localized force applied thereto by the
side plates 359 of the prior art gripping element 300. Scratching
and shearing damage into the well wall 195 is evident.
[0033] Continuing with reference to FIGS. 2 and 3, wearing and
damage to the gripping element 100 and the well wall 195 may be
substantially avoided by the presence of an arcuate surface 201
which contacts the well wall 195 as proposed by embodiments of the
present invention. The arcuate surface 201 is configured in light
of the arcuate nature or character of the well 197. In fact, the
arcuate surface 201 may be configured with a radius based on the
particular arcuate dimensions of the given well 197 (e.g. its
diameter).
[0034] For example, in one embodiment, the well 197 is about 8.5
inches in diameter, as formed by a conventional 8 inch drill bit.
Therefore, the gripping element 100 may be configured with an
arcuate surface 201 displaying about a 4.25 inch radius. Thus, the
arcuate surface 201 will be of a shape that substantially matches
the shape of the well wall 195. As a result, the force of the
gripping element 100 against the well wall 195 during operation of
the tractor 101 may be substantially evenly distributed. Thus,
uneven wearing of the gripping element 100 is unlikely and the
possibility of damage to the well wall 195 from the operation is
minimized. In fact, minimizing the possibility of damage to the
well wall 195 in this manner, may improve the viability of open
wells with softer formations that might otherwise be considered
inoperable for tractoring operations.
[0035] While the above is described with reference to an 8.5 inch
diameter well 197, other well sizes are common such as those that
are about 6.5 inches in diameter and those that are about 10.5
inches in diameter drilled from bits that are roughly of the 6 inch
and 10 inch variety respectively. Thus, embodiments of the gripping
element 100 may be configured with an arcuate surface 201
displaying a radius that is about 3.25 inches or about 5.25 inches
to match such well sizes. Additionally, a host of other arcuate
surface 201 radii may be employed depending on the diameter of the
well 197. So long as the arcuate surface 201 is configured based on
the arcuate character of the well 197 involved, benefits of the
described embodiments may be realized.
[0036] As indicated, the arcuate surface 201 may be selected based
on the diameter of the well 197 involved. However, as detailed
further below, this does not necessarily require that the arcuate
surface 201 be entirely continuous or of substantially the same
radius as that of the well 197 in order to minimize damage to the
well wall 195 or wear at the edges of the arcuate surface 201. For
example, the presence of an arcuate surface 201 sufficient to
provide majority contact at the interface 275 between the gripping
element 100 and the well wall 195 may be one of several manners of
employing an arcuate surface 201 configured based on the arcuate
character of the well 197. As detailed below, this remains so even
with a minimal degree of dig into the wall 195 by the element
100.
[0037] By way of example, given the above scenario of an 8.5 inch
diameter (4.25 inch radius) open well 197 through a soft formation
199, significant benefit may be realized from employing a
non-matching arcuate surface 201, for example, displaying a 3.25
inch radius. That is, in spite of the arcuate surface 201 having a
radius that is about an inch different from that of the well 197,
less than about 1 mm of dig into the soft well wall 195 will result
in the majority of the arcuate surface 201 being in stable direct
contact with the well wall 195. This is unlike the flat surface of
the prior art gripping element 300 which would require
deterioration of the well wall 195 across the majority of the
interface 375 in order to provide majority contact between the flat
surface and the well wall 195 (see FIG. 3). Therefore, with the
significant difference in these two scenarios in mind, the arcuate
surface 201 of the embodiment described here may still be referred
to as substantially matching the arcuate shape of the well 197
(i.e. in spite of the noted inch difference in radii). Stated
another way, an arcuate surface 201 having a radius that is within
about an inch of a radius of the well 197 may be considered
substantially matching the arucate shape of the well wall 195.
[0038] As shown in FIG. 2, the gripping element 100 may be made up
of primarily a monolithic or integrally formed body 200 providing
an arcuate surface 201 based on the dimensions of the well 197.
However, as alluded to above, providing an arcuate surface 201
based on the well does not necessarily require an entirely
continuous surface. For example, the prior art gripping element 300
fails to provide an arcuate surface at its interface 375 with the
well wall 195. Nevertheless, a new embodiment of a gripping element
400 may be provided with such a segmented body. For example, the
gripping element 400 may be formed by a plurality of stamped plates
459-462 held together by a pin 250 and rollers 225, wherein each
successive interior plate 460-462 is incrementally taller than its
outer-more adjacent plates. As such, the innermost plates 462 are
taller than plates 461, which are taller than plates 460, which are
taller than side plates 459. Thus, in combination, the plates
459-462 form an arcuate surface 401 across the width of the
gripping element 400 formed by the plates, wherein the arcuate
surface 401 is configured based on the arcuate character and
dimensions of the well 197. Notes that although, the gripping
element 400 of FIG. 4 is depicted as having eight stamped plates
459-462, in alternative embodiments, the gripping element 400 may
have any desired number of plates arranged in any appropriate
lateral arrangement. For example, a lateral spacing may exist
between every other plate.
[0039] In an embodiment shown in FIG. 5, a monolithic body 500 is
provided having a male region 575, a female region 525 and a middle
region 550, wherein both the male 575 and female 525 regions
include multiple arcuate shaped teeth 510. Such bodies 500 may be
connected end to end as shown in FIG. 6 to form a continuous chain
or track 675. Such regions may be connected by a pin 250 and
rollers 225. As shown, the male region 575 of each body 500 is
sized to fit within a female region 525 of each adjacent body 500.
In addition, the teeth on the pinned male 575 and female 525
regions may be aligned such that across the width of the track 675,
the male 575 and female 525 regions combine to form substantially
continuous teeth 510. Note also that the width of the track 675
contains only two junctions 680 between pinned bodies 500. This is
in comparison to the seven junctions 380 formed by the plates of
the prior art gripping element 300, the significance of which is
described below.
[0040] In still another embodiment, the gripping element may
include a monolithic body that nevertheless displays a degree of
discontinuity at the arcuate surface thereof. For example, an
additional roller may be positioned at the center of the male
region 575 of the monolithic body. This may aid the track 675 in
its translation across the well wall 195 and enhance the
interaction of the track 675 and the tractor's driving mechanism.
However, in such a circumstance a channel would be provided into
the surface of the track 675 in order to accommodate the added
roller at each gripping element. However, such a channel would
traverse the arcuate surface of each gripping element leaving a gap
or break in contact between the arcuate surface and the well wall
195.
[0041] In spite of the slight interruption of physical contact
between the arcuate surface and the well wall 195 in the embodiment
described above, the arcuate surface may still be considered as
configured based on the arcuate character of the well wall 195. In
fact, the arcuate surface 201 may be said to be substantially
matching the dimensions of the well 197. For example, in one such
embodiment with a central roller, the arcuate surface is configured
to make continuous contact with the well wall 195 at between about
50% and about 97% of the interface even with the presence of the
indicated channel. As a result, the probability of wear at the
outer edges of the gripping element or damage to the well wall 195
by the gripping element may be minimized. Thus, as with other
embodiments described above, substantial benefit may be realized in
spite of a degree of discontinuity in the arcuate surface.
[0042] Continuing now with reference to FIG. 6, an upper surface of
the track 675 for use with the tractor 101 of FIG. 1 is shown. In
such an embodiment, the entirety of the upper surface of the track
675 is arcuate, and specifically each tooth 510 which extends
across the width of the track 675 is arcuate. As such, each tooth
510 forms the arcuate surface 200 shown in FIG. 2. The series of
"y-shaped" gripping elements 500 reveals a host of teeth 510 as
indicated above for gripping and pulling along a well wall 195 such
as shown in FIG. 2. In fact, in the embodiment shown, each gripping
element 500 includes teeth 510 at its middle region 550, female
region 510, and male region 575. The "y-shaped" gripping elements
500 are aligned akin to overlapping chain links to form the track
675.
[0043] In an alternate embodiment, such as that shown in FIG. 7,
the gripping elements 700 are composed of alternating male 775
(i.e. "t-shaped") and female 725 (i.e. "H-shaped") sections. In
such an embodiment the male 775 and female 725 sections of the
gripping elements 700 may be alternatingly positioned to form a
track for use with the tractor 101 of FIG. 1. In another
alternative embodiment, such as that shown in FIG. 8, each gripping
element 800 contains both female and male interlocking
portions.
[0044] Referring back to FIGS. 5 and 6, of the regions 550, 525,
and 575 described above, the middle region 550 includes the widest
portion of the monolithic body 200 and is the segment of the
gripping element 100 that is depicted in FIG. 2. A tooth 110
traversing this region 550 of the gripping element 100 is formed
entirely by a sole gripping element 100 without contribution from
adjacent elements 100. Thus, such a tooth 110 may be advantageously
devoid of lateral interfacing, a benefit detailed further
below.
[0045] Referring again now to FIGS. 2 and 3, advantages of
employing a gripping element 100 having a monolithic body 200 in
comparison to a gripping element 300 with a body formed of separate
plates 359, 360, are described. That is, in addition to readily
providing a substantially uninterrupted arcuate surface 201, other
benefits may be realized by employing a gripping element 100 made
up primarily of a monolithic body 200.
[0046] As shown in FIG. 3, the prior art gripping element 300
includes a body that is made up of stacked plates 359, 360. As a
result, a plurality of lateral interfaces 380 are present across
the element 300. Each such interface 380 presents a location
available for the accumulation of dirt and debris and friction
which may affect the performance of a downhole tractor operation.
For example, in the case of the prior art gripping element 300
shown in FIG. 3, debris would be able to reach all the way to the
interface of the pin 350 which is configured for rotation through
the plates 359, 360.
[0047] The efficiency of such rotation may be affected by the
described accumulation of debris. Given that the tractor operation
may be focused at an open well wall 195 in direct contact with
earth formations 199, the possibility of accumulation of debris in
this manner may be very likely. For example, it would be common for
corrosive chemicals, dust, suspended sand, rock, mud, drilling
fluid additives and other debris to be present within a
conventional open hydrocarbon well 197. Use of a monolithic body
200 as described above minimizes the interfacing 380 that is found
within the body of a prior art gripping element 300 as shown in
FIG. 3. For example, in the embodiment of FIGS. 5 and 6, the main
body 550 of each gripping element 500 contains no interfaces, while
the male 575 and female 525 regions interface at only two places
across the track 675 width.
[0048] Even without the accumulation of debris, the presence of
such a high amount of lateral interfacing in the prior art gripping
element 300 of FIG. 3 means that the pin 350 is forced to traverse
a host of plates 359, 360. Use of a monolithic body 200 on the
other hand, as shown in FIG. 2, provides added stability and avoids
the possibility of independent translation or rotation of plates
359, 360. As a result, the efficiency of pin rotation is not
frictionally compromised by competitively shifting plates 359, 360
of the body of the gripping element 100. By providing the
monolithic body 200 to the gripping element 100 the challenges
presented by a significant amount of lateral interfacing as
described here may be largely avoided.
[0049] The embodiments described hereinabove significantly address
problems of wear and breakdown of tracks and gripping element links
thereof for a downhole tractor. In particular, problems of uneven
wear on gripping elements resulting from the arcuate character of a
well wall are substantially avoided along with the problem of wear
on the well wall imposed by the gripping element. As a result,
occurrences of track failure or inefficiency during a downhole
tractoring operation may be minimized and the integrity of the well
wall maintained. This may be of significant benefit in the case of
open wells, especially those traversing softer formations. By
protecting the integrity of the well wall and the gripping
elements, time spent on equipment repair in the field may be saved.
Furthermore, the availability of tractoring embodiments described
herein may improve the viability of open wells through softer
formations previously thought inoperable for tractoring
operations.
[0050] The preceding description has been presented with reference
to presently preferred embodiments of the invention. Persons
skilled in the art and technology to which this invention pertains
will appreciate that alterations and changes in the described
structures and methods of operation can be practiced without
meaningfully departing from the principle, and scope of this
invention. Accordingly, the foregoing description should not be
read as pertaining only to the precise structures described and
shown in the accompanying drawings, but rather should be read as
consistent with and as support for the following claims, which are
to have their fullest and fairest scope.
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