BACKGROUND

[0001] Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on efficiencies associated with well completions and maintenance over the life of the well. Along these lines, added emphasis has been placed on well logging, profiling and monitoring of conditions from the outset of well operations. Whether during interventional applications or at any point throughout the life of a well, detecting and monitoring well conditions has become a more sophisticated and critical part of well operations.

[0002] Initial gathering of information relative to well and surrounding formation conditions may be obtained by way of a logging application. That is, equipment at the surface of an oilfield adjacent to the well may be used to deploy a logging tool in the well. Alternatively, straight forward temperature measurements may be taken by use of a fiber optic line or tether. For example, as opposed to a generally more complex logging application, a distributed temperature survey (DTS) may be undertaken with use of a fiber optic tether that may take location specific well temperature readings without the requirement of an associated logging tool.

[0003] In the case of a vertical well, the fiber optic tether may be directly dropped into the well for sake of running a DTS application as noted above. However, where the well is deviated, a conveyance aid such as coiled tubing is generally utilized to help advance the tether through tortuous regions of the well. For example, the tether may be jacketed by a metal tube and run through several thousand feet of coiled tubing. Thus, as the coiled tubing is forcibly injected through the tortuous well, the fiber optic tether is also brought along for sake of the DTS application.

[0004] Unfortunately, coiled tubing is a dramatically cumbersome undertaking, particularly for the sake of no more than advancing a small lightweight fiber optic slickline through the well. Large scale equipment must be delivered to the oilfield surface and properly rigged up in order to inject the coiled tubing. Once more, the coiled tubing introduces a substantial restriction into the well. That is, the coiled tubing may occupy between about 1-3 inches in diameter of a well that is likely well under 12 inches in diameter in certain locations. The degree of obstruction here seems noteworthy when considering that for sake of the DTS application all that is required is conveyance of a fiber optic tether that is generally under 0.125 inches in diameter.

[0005] With the above drawbacks in mind, fiber optics for a DTS application may be incorporated into a more conventional wireline conveyance. For example, the wireline may be conveyed through tortuous well sections by way of conventional tractoring equipment. Specifically, a tractor may be powered by an electrical cable run from the oilfield surface that also incorporates fiber optics for sake of the noted DTS application. Indeed, the wireline cable may include a variety of power and communicative lines along with a host of isolating and protective polymer layers. As a result, the cable may be of relatively substantial weight, strength, and profile.

[0006] Unfortunately, the use of such cables as described above again means that the equipment positioned at the surface of the oilfield may be fairly substantial in terms of footprint and power requirements therefor. Similarly, the set up and performance cost of running the operation may also be quite significant. Further, while somewhat smaller than coiled tubing, running such wireline still presents a substantial obstruction to the well. For example, it would not be unexpected for the line to be about 0.5 inches in diameter, well beyond what should actually be required for a slickline based fiber optic DTS application.

[0007] Presently, even though all that may be sought is a seemingly lightweight slickline DTS application, if the well is deviated, the operator's choice is between one cumbersome equipment option or another. That is, either the large scale mobilization of coiled tubing equipment is required or the large scale mobilization of a heavy wireline cable and equipment is required. Either way, the well is more obstructed during the application and costs are substantially greater due to the added equipment expenses.

SUMMARY

[0008] A tractor system is provided. The tractor system includes a downhole power source-operated tractor assembly that is configured for use in a horizontal section of a well. A fiber optic slickline is coupled to the tractor assembly for obtaining measurements from the well. Additionally, the tractor assembly operates at an efficiency of greater than about 30%, for example through use of discontinuous arm actuation techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 A is a side view of an embodiment of a fiber optic slickline and tractor system.

[0010] Fig. IB is a side cross-sectional view of the system of Fig. 1A revealing arm and conveyance actuation features for tractoring thereof.

[0011] Fig. 2A is an enlarged view of the arm and conveyance features of Fig. IB with tractor arms in a retracted position.

[0012] Fig. 2B is an enlarged view of the arm and conveyance features of Fig. 2A with the tractor arms in an expanded position. [0013] Fig. 3 is an overview of an oilfield with a deviated well accommodating the fiber optic slickline and system of Fig. 1.

[0014] Fig. 4 is a perspective view of the system of Fig. 3 in the well with expanded tractor arms for centralizing and advancing of the system through the well.

[0015] Fig. 5 is a flow-chart summarizing an embodiment of utilizing a fiber optic slickline and tractor system.

DETAILED DESCRIPTION

[0016] Embodiments are described with reference to certain tools and applications run in a well over a fiber optic slickline. As used herein, the term "slickline" is meant to refer to an application that is run over a conveyance line that is substantially below about 0.25 inches in overall outer diameter and devoid of powered electrical communication. That is, as opposed to a higher profile or diameter wireline cable with a power line running therethrough, downhole applications detailed herein are run over a lower profile slickline lacking such capacity. The type of surface equipment dedicated to the slickline applications may be a fairly mobile and of a comparatively smaller footprint as compared to that required for wireline applications, discussed in more detail below. For example, the embodiments detailed herein utilize a fiber optic slickline for sake of distributed temperature survey (DTS) applications. However, such a fiber optic slickline may be coupled to a downhole tractor and other tools that are of efficiencies tailored to run on conventional downhole batteries without reliance on surface delivered power for sake of operation. Further, measurements apart from temperature may be attained in manners detailed herein. For example, distributed pressure, strain, and/or vibration surveys applications may also be performed utilizing tools and techniques detailed herein.

[0017] Referring specifically now to Fig. 1A, a side view of an embodiment of a fiber optic slickline and tractor system 100 is shown. The system 100 includes a battery operated tractor 101, which may be, without limitation, about 10-20 feet in length, which is connected to a fiber optic slickline 110 as alluded to above. The slickline 1 10 is of lightweight construction and may be, without limitation, between about 0.1 and 0.15 inches in diameter. The slickline 110 may include multiple fiber optic threads within a protective tubular structure. For example, one thread may be dedicated to telemetry such as for tractor communications, whereas another is dedicated to downhole measurements as detailed herein, with still others provided for sake of redundancy and/or backup usage, etc. Regardless, as shown in Fig. 1, the tractor 101 includes an interface 125 for accommodating a battery 120. Thus, while communications between the tractor 101 and equipment at an oilfield 300 may be served over the fiber optic slickline 110, power requirements for actually running the tractor 101 may be met by the battery 120 (see Fig. 3). So, for example, where a DTS application utilizing the slickline 110 is run in a deviated well 380 as shown in Fig. 3 and detailed further below, the tractor 101 may serve as an aid to conveying the line 1 10 through the deviated well section. In an embodiment, the system 100 comprises a downhole embedded power source other than a battery 120 to power the tractor 101 such as, without limitation, a hydraulic accumulator, a fuel cell, or the like.

[0018] In Fig. 1A an embodiment of the tractor 101 is shown as a wheeled tractor comprising elements or arms 135 configured to extend outwardly from the tractor 101 and are shown in an expanded state in Fig. 1A. With added reference to Fig. 4, the arms 135 accommodate rollers or wheels 137 that are configured for gripping a wall 400 of a well 380. Thus, as the powered rollers 137 are turned, the tractor 101 may help the system 100 advance (or retreat) in the well 380.

[0019] As depicted, the expanded arms 135 of the tractor 101 are visible at a first drive section 130 thereof. However, the tractor 101 is also outfitted with another, second, drive section 140. Further, any practical number of additional drive sections may also be incorporated. Regardless, the depicted second drive section 140 is also equipped with arms 135 and rollers 137 as is apparent in the perspective view of the tractor 101 in Fig. 4. However, for sake of providing centralization as detailed further herein, the arms 135 of the different drive sections 130, 140 may be perpendicular to one another. Thus, in the side view of Fig. 1A, where the arms 135 of the first drive section 130 are entirely visible, those of the second drive section 140 are not apparent.

[0020] Continuing with reference to Fig. 1A, the tractor 101 is also outfitted with a hydraulic section 175. That is, while the rollers 137 may be powered by the battery 120 as needed, hydraulic control over arm actuation may be utilized to substantially reduce the overall power requirements of the tractor 101 as detailed further below. As a result, the tractor 101 may be an effective and practical conveyance aid even though the power available to the tractor 101 is limited to what is available from conventional downhole batteries.

[0021] Referring now to Fig. IB, a side cross-sectional view of the system 101 of Fig. 1A is shown. In this view, roller 137 and arm 135 actuation features are more apparent. For example, a motor 132 of the first drive section 130 is shown. The motor 132 is solely powered by the battery 120, which may be a conventional lithium ion type fit for downhole use. In one embodiment, the battery 120 is rechargeable. Further, even when accounting for another motor at the second drive section 140, the entire tractor 101 may operate at between about 150 and 300 watts which is sufficiently met by the downhole battery 120. The tractor 101 may be of an efficiency rating of at least about 30%. That is to say, less than about 70% of power consumed by the tractor 101 during operation may be attributed to heat and other non-performance losses. Additionally, in one embodiment, the battery 120 may be of a stackable configuration. That is, one or more additional battery modules may be provided in series so as to increase power availability to the tractor 101. [0022] The motors 132 are utilized to drive the rollers 137 as indicated above. Additionally, the hydraulic section 175 is motor powered. For example, as detailed below with reference to Figs. 2A and 2B, a pump of the hydraulic section 175 may be motor powered to direct the arms 135 open. However, due to hydraulic regulation, the arms 135 may be hydraulically locked in an open position once expanded. Thus, a continuous power drain on the battery 120 need not take place in order to maintain the arms 135 in an open position.

[0023] In the embodiment shown, the hydraulic section 175 includes a compensator or accumulator 160 to display hydraulic suspension behavior. So for example, where arms 135 in a locked open position encounter a restriction in the well 380, a small degree of temporary arm compression may take place so as to allow the tractor 101 to navigate the restriction. The end result is that, even though continuous motor drive is not used to maintain the arms 135 in an open position, the expanded arms 135 may display a similar type of responsiveness to potentially changing profile of the well 380 (see Figs. 3 and 4).

[0024] Referring now to Fig. 2A, an enlarged view of the arm and conveyance features of Fig. IB are shown. Specifically, the internals of the first drive section 130 of the tractor 101 are shown as they would appear with the tractor arms 135 in a retracted position. The hydraulic section 175 of Figs. 1A and IB may be motor powered as described above (e.g. for regulating the expansion of the arms 135). Similarly, the depicted motor 132 is also in direct mechanical communication with the rollers 137 of Figs. 1A and IB for rotation thereof to drive the tractor 101. However, as described further below, the separate functions of roller rotation and arm actuation are intentionally disassociated for sake of maximizing tractor efficiency in terms of power requirements. [0025] Continuing with reference to Fig. 2A, with added reference to Fig. IB, the motor 132 is linked to the rollers 137 through a rotating shaft 210 that interfaces gearing 250 ultimately reaching the rollers 137, though alternate mechanical linkage architecture may be used. Regardless, surface directed actuation of the rollers 137 may take place via communication over the slickline 110. Similarly, motor powered fluid communication with the hydraulic section 175 may translate into hydraulic control over the position of a linear piston 225 that serves to open or expand the arms 135 to the position shown in Fig. 2B. However, since this function is regulated through the hydraulic section 175, a pump need not be continuously driven to keep the arms 135 open.

[0026] With specific reference to Fig. 2B, an enlarged view of tractor internals are depicted with the arms 135 in an expanded or open position. In the embodiment shown, this is achieved through hydraulic shifting of the linear piston 225 in an uphole direction. When this occurs, actuator rods 275 coupled to the piston 225 are pulled upward in a manner that shifts open the arms 135 about an axis at the above-noted gearing 250. Of course, alternative types of architecture and/or orientation may be utilized. However, by utilizing some form of intervening hydraulics to actuate opening of the arms 135, the opportunity to hydraulically lock the arms in the open position is now available. Thus, dramatic savings may be realized in terms of power consumption and battery life.

[0027] So, for example, at the appropriate time an operator at an oilfield 300 may send data over the fiber optic slickline 1 10 to direct the battery powered driving of a pump of the hydraulic section 175 to open the arms 135 as described (see Figs. IB and 3). Once opened, the operator may now direct a hydraulic locking of the arms 135 in the open position such that no further motor drive or power is required in order keep the arms in this open position. [0028] Continuing with added reference to Fig. IB, with the arms 135 expanded the operator may now signal the motor 132 to drive rotation of the rollers 137 through the rotating shaft 210 and gearing 250. Thus, when engaged with a well wall 400 as shown in Fig. 4, an aid to system 100 advancement through the well 380 is now provided. Indeed, the motor 132 may also be directed to rotate the rollers 137 in a reverse direction to help in removal of the system 100 from the well 380. Although, it may be more common to direct opening of the hydraulic lock to allow collapse or retraction of the arms 135 followed by winch driven removal of the entire system 100 from the well 380 by pulling uphole on the slickline 1 10 (see Fig. 3). While embodiments of the tractor 101 are shown as wheeled tractors comprising drive sections 130 and 140 utilizing arms 135 and rollers 137, the fiber optic slickline 110 and system 100 may utilize a tractor 101 having drive sections similar a reciprocating-type tractor, such as that shown in U.S. Patent No. 6,629,568, incorporated by reference herein in its entirety, while remaining within the scope of the present disclosure. In such an embodiment the battery may be utilized to power hydraulic section, similar to the hydraulic section 175, which may be locked utilizing an accumulator, such as the accumulator 160 noted hereinabove. In an embodiment, manipulation of the slickline 110 may be utilized to advance and/or assist in advancing the system 100 through the wellbore.

[0029] Referring now to Fig. 3, an overview of an oilfield 300 is shown with a deviated well 380 that accommodates the fiber optic slickline 110 and system 100 of Fig. 1. In the embodiment shown, the tractor 101 of the system 100 is utilized to help convey the slickline 110 through the deviated portion of the well 380 in order to carry out a DTS application. Thus, information regarding well characteristics may be acquired by fiber optics of the slickline 110 and and performance characteristics of the tractor 101 may be transmitted from the tractor 101 and analyzed by a processor of a control unit 330 at the surface of the oilfield 300. The slickline 110 also may be configured Additionally, in other embodiments, a service tool 145 or other application device may also be secured to the tractor for carrying out additional applications in the well 380 as directed over the slickline 1 10 and/or powered by the downhole battery 120 as shown in Figs. 1A and IB. The service tool 145 may comprise, but is not limited to, a mechanical services tool configured for plug setting or for manipulating downhole completion components, a logging tool, a perforating tool, or any suitable downhole tool.

[0030] Fiber optic communications to a receiver of the tractor 101 from the control unit 330 may be sent over the slickline 110 to direct and control specific maneuvers during conveyance, such as in response to performance characteristics transmitted to the control unit 330 from the tractor 101 along the slickline. Specifically, the drive sections 130, 140 of the tractor 101 may be directed independently or in concert as described hereinabove. For example, advancement of the system 100 may cease, the arms 135 opened, locked, and the rollers 137 rotated to begin aiding conveyance as the tractor 101 approaches the horizontal well section, all directed from the surface-based control unit 330.

[0031] In the embodiment shown, a truck 325 is utilized to accommodate the noted control unit 330 along with a spool 340 of fiber optic slickline 1 10. While other delivery modes may be utilized, the type of surface equipment dedicated to the application may be a fairly mobile and of a comparatively smaller footprint (with respect to typical wireline or coiled tubing surface equipment) given the lightweight nature of the slickline 1 10. Further, the use of a suitable battery powered tractor 101 that is compatible with the slickline 110 avoids detracting from the small profile and lightweight advantages of the slickline 1 10. More specifically, the slickline 1 10 is run past a conventional rig 350 and pressure control equipment 375. Casing 385 defining the deviated well 380 traverses various formation layers 390, 395 perhaps extending several thousand feet in depth. Yet, the highly efficient, power saving tractor 101 is capable of pulling the slickline 110 throughout the well 380 for the DTS application, perhaps even serving as an aid to withdrawal of the system 100 when the application is completed. In an embodiment where two drive sections 130, 140 are utilized as depicted, a pull force of 200 - 300 lbs. may be available with an expected speed of more than about 1,000 ft. per hour provided.

[0032] Referring now to Fig. 4, a perspective view of the system 100 of Fig. 3 is shown in the well 380. In this view, the expanded tractor arms 135 of both drive sections 130, 140 are simultaneously visible. In addition to the interfacing at the well wall 400 that is apparent between teeth of the rollers 137 and the casing 385 for sake of conveyance, the orientation of the drive sections 130, 140 relative one another is now more apparent. More specifically, the role of centralizing the tractor 101 in the well 380 is more clear with each section 130, 140 of a substantially perpendicular orientation (with respect to a longitudinal axis of the tractor 101) to the next, thereby preventing the tractor 101 from becoming misaligned from a central axis of the well 380.

[0033] The view of the tractor 101 in the well 380 as shown in Fig. 4 also reveals its generally small profile. That is, the tractor 101 may operate on no more than a downhole battery 120 as detailed above (see Figs. 1A and IB). Thus, it may be fairly small, with a body of perhaps between about 2 - 3.5 inches in overall diameter (d). This is in contrast to an overall well diameter (D) that is likely to exceed 10 inches. So, for example, in contrast to a larger coiled tubing operation, the flow rate of the well 380 is unlikely to be substantially affected by the presence of the tractor 101 or the slickline 1 10 (see Fig. 3). Similarly, the slickline 1 10 of Fig. 3 is not separated from the well environment by coiled tubing. Thus, a more accurate DTS application may take place, with readings likely within about 3°F of actual temperature, in addition to one that is less cumbersome and more cost-effective. In addition to or complementing the distributed temperature, distributed pressure, distributed strain, and/or distributed vibration measurements, in an embodiment, the tractor 101 may convey the slickline 110 to a predetermined location within a well, such as the well 380 and remain in the predetermined location for a predetermined length of time in order to perform a production logging operation. Such a production logging operation may be performed utilizing distributed temperature, distributed pressure, distributed strain, and/or distributed vibration measurements without substantially occluding the well 380 during production therefrom.

[0034] Referring now to Fig. 5, a flow-chart summarizing an embodiment of utilizing a fiber optic slickline and tractor system is depicted. In the embodiment shown, the system is deployed into a well as indicated at 515 and utilized in an application to acquire well information (see 525). For example, a DTS application may be run with well temperature profiling taking place directly through a fiber optic slickline of the system. Indeed, such data acquisition may ensue as soon as the system is deployed into the uppermost vertical section of the well.

[0035] Given that the system is also outfitted with a battery operated tractor assembly, applications such as the noted DTS may also be run in any deviated section of the well. Specifically, without any direct power from surface, arms of the tractor may be opened as indicated at 535 to begin engagement with a wall of the well. As a matter of enhancing power efficiency, the arms are opened and may even be locked in position in a hydraulic fashion (see 545). Thus, as indicated at 555, rollers on the arms may be directed to rotate and aid in advancement of the tractor and system through the deviated section of the well. In one embodiment, the hydraulics of the system incorporate an accumulator that allows for a degree of arm collapse upon encountering a predetermined amount of resistive force. So, for example, as the tractor encounters a restriction, the arms may collapse radially inwardly to a predetermined degree to allow for the continued advancement of the tractor as opposed to having the entire system stuck in place at the location of the restriction.

[0036] As indicated at 565, additional, perhaps more directly interventional, applications may also be performed with a service tool that is incorporated with the system. Regardless, once the downhole applications are completed, the system may be removed from the well. More specifically, the rollers may be directed to cease any advancing rotation, the hydraulic lock lifted, and the arms retracted into the body of the tractor, with each of these maneuvers directed over the fiber optics of the slickline. Thus, as indicated at 575 the entire system may be pulled out of the well in a winch- driven fashion by a spool at the oilfield surface adjacent the well. Additionally, in an embodiment as indicated at 585, roller rotation may be reversed with the arms remaining in an open position to serve as a further aid to withdrawal of the system from the well. This type of aided withdrawal may serve as a safeguard against damage to the lighter weight slickline.

[0037] Embodiments of the fiber optic slickline and tractor system detailed herein allow for avoiding the use of heavier cables and correspondingly larger tractors where the operator is faced with running a DTS or other low power application in a deviated well. Similarly, the use of coiled tubing may also be avoided. Thus, the time, expense and footspace dedicated to large scale interventional equipment may also be avoided. Indeed, even the amount of wellbore space that is occupied during downhole applications run over the fiber optic slickline and tractor system may be kept to a minimum. Thus, flow through the well during such applications may remain largely unobstructed. In an embodiment, the fiber optic slickline may be deployed within the flow path of a coiled tubing and the tractor system of the present disclosure may be attached to the downhole end of the coiled tubing to aid in tractoring the coiled tubing through a wellbore, such as a deviated wellbore or the like.

[0038] The preceding description has been presented with reference to presently preferred embodiments. Persons skilled in the art and technology to which these embodiments pertain will appreciate that alterations and changes in the described structures and methods of operation may be practiced without meaningfully departing from the principle, and scope of these embodiments. Regardless, 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.