Patent Publication Number: US-2016237812-A1

Title: Fiber Optic Slickline and Tractor System

Description:
BACKGROUND 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     Presently, even though all that may be sought is a seemingly lightweight slickline DTS application, if the well is deviated, the operator&#39;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 
     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 
         FIG. 1A  is a side view of an embodiment of a fiber optic slickline and tractor system. 
         FIG. 1B  is a side cross-sectional view of the system of  FIG. 1A  revealing arm and conveyance actuation features for tractoring thereof. 
         FIG. 2A  is an enlarged view of the arm and conveyance features of  FIG. 1B  with tractor arms in a retracted position. 
         FIG. 2B  is an enlarged view of the arm and conveyance features of  FIG. 2A  with the tractor arms in an expanded position. 
         FIG. 3  is an overview of an oilfield with a deviated well accommodating the fiber optic slickline and system of  FIG. 1 . 
         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. 
         FIG. 5  is a flow-chart summarizing an embodiment of utilizing a fiber optic slickline and tractor system. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     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  110  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  110  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. 
     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 . 
     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. 
     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. 
     Referring now to  FIG. 1B , 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 . 
     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. 
     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 ). 
     Referring now to  FIG. 2A , an enlarged view of the arm and conveyance features of  FIG. 1B  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 1B  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 1B  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. 
     Continuing with reference to  FIG. 2A , with added reference to  FIG. 1B , 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. 
     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. 
     So, for example, at the appropriate time an operator at an oilfield  300  may send data over the fiber optic slickline  110  to direct the battery powered driving of a pump of the hydraulic section  175  to open the arms  135  as described (see  FIGS. 1B 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. 
     Continuing with added reference to  FIG. 1B , 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  110  (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. Pat. 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. 
     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  110  and/or powered by the downhole battery  120  as shown in  FIGS. 1A and 1B . 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. 
     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 . 
     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  110 . 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  110 . 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  110 . More specifically, the slickline  110  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. 
     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 . 
     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 1B ). 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  110  (see  FIG. 3 ). Similarly, the slickline  110  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. 
     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. 
     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. 
     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. 
     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. 
     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.