US 20080202769 A1
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.
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
3. The driving mechanism of
4. The driving mechanism of
a rotable pin through said body; and
rollers secured at ends of said rotable pin.
5. The driving mechanism of
6. The driving mechanism of
7. The driving mechanism of
8. The driving mechanism of
9. The driving mechanism of
an expansion mechanism for engaging said track with the well wall.
10. The driving mechanism of
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
13. The downhole tractor of
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
16. The gripping element of
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
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.
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.
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.
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
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
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).
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.
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.
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.
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.
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.
Referring now to
The downhole tractor 101 of
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.
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.
A downhole tractor 101 such as that of
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.
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
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
Continuing now with reference to
As shown in
Continuing with reference to
Unlike the substantially matching and smooth interface 275 between the arcuate surface 201 and the well wall 195 as shown in
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.
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
Continuing with reference to
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.
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.
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.
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
As shown in
In an embodiment shown in
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.
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.
Continuing now with reference to
In an alternate embodiment, such as that shown in
Referring back to
Referring again now to
As shown in
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
Even without the accumulation of debris, the presence of such a high amount of lateral interfacing in the prior art gripping element 300 of
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.
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.