You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
     Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming, and ultimately very expensive endeavors. As a result, over the years, a significant amount of added emphasis has been placed on well monitoring and maintenance. Once more, perhaps even more emphasis has been directed at initial well design and construction. All in all, careful attention to design and construction efficiencies may help maximize return on the substantial investment dedicated to oilfield operations. 
     In the case of well construction, careful attention and planning may be devoted to the specific architecture, drilling, casing and other hardware installations involved in what is generally referred to as ‘completions’ operations. Completions operations generally involve the positioning of large scale surface equipment at the oilfield. For example, a rig is located over a well head to serve as a platform for equipment access in drilling the well, installing various hardware or downhole devices, or to provide access for later well interventions. 
     In the case of initial installations, a variety of tubulars are often provided downhole from the rig floor. For example, casing segments to help support and define the well may be transported one by one into the well from the rig floor. This is no small feat given that each 20-40 foot casing segment is generally several thousand pounds of stainless steel tubing, up to a few feet in diameter. Thus, even getting the segments safely and efficiently to the rig floor for subsequent well installation is no small feat. 
     The noted heavy casing is generally pulled to the area of the rig floor by way of a rig elevator which may consist of a strap or cable at the end of a crane. That is, an operator at the rig floor may secure the strap about a collar of the casing segment thereby allowing the segment to be pulled upward to a vertical position for subsequent delivery into the well. Due to the massive size of the casing, a positioning system, generally referred to as a ‘Laydown’ or ‘Pickup’ Machine, is often used to convey each tubing segment to the vicinity of the rig floor where the noted strap may then be employed to pull the segment up vertically above the floor. 
     Unfortunately, a pickup machine is a large footspace eating piece of heavy immobile equipment, generally disposed at the oilfield surface on a skid. It may take several operators and multiple 18 wheelers to deliver, position and operate this equipment along with managing a supply of casing tubulars from an associated pipe rack. Once more, in spite of robust construction, the pickup machine is particularly prone to wear and failure. Specifically, a considerable amount of time and effort is dedicated to ensuring that a gantry system of rollers remains operable. This roller system is utilized to extend a trough accommodating each casing segment, one by one, toward the rig floor. Due to the amount of weight accommodated and the moving parts involved, such a system is prone to rapid wearing. 
     In addition to the massive size and failure modes of a pickup machine, it is also a very expensive piece of equipment, perhaps upwards of $250,000 in today&#39;s numbers. Once more, such drawbacks are particularly noteworthy where smaller, lighter weight specialty tubulars are involved. For example, even where lighter weight, say 500-600 lb. production tubing, is to be installed, the same type of large-scale pickup machine is generally employed. This is because, in spite of the lighter weight, such specialty tubing segments are generally of similar lengths, thus benefitting from the trough type of loading and extension delivery to the area of the rig floor. 
     Trough loading and extension also provide vastly improved safety as compared to say strap pickup from the oilfield surface. For example, a broken strap with the tubular resting at least partly more stably in a trough is much less likely to result in operator injury than a broken strap with the tubular fully suspended in mid air, perhaps 10 feet or more off the ground. As a result, even though the pickup machine is particularly prone to wear of its gantry system and may constitute overkill in terms of delivery capacity when utilized for lighter specialty tubulars, it nevertheless remains the preferred mode of tubular delivery to the rig floor. 
     SUMMARY 
     A downhole tubular positioning system is provided. The system is configured for locating at an oilfield surface in conjunction with a rig to aid in delivery of downhole tubular to a well. A mobile lift frame and trough are included with the system. More specifically, the lift frame is configured for elevating to a level approaching that of a floor of the rig. The trough is coupled to the lift frame so as to accommodate a tubular. Once more, the trough is coupled to the lift frame in a sledded manner so as to be slidably extended toward the rig floor. The sledded coupling of the trough to the frame may include unique interfacing. For example, the interfacing may include a runner or broader slider surfaces. In one embodiment, multiple discrete polymeric shoes serving as runners may extend from an underside of the trough for engagement with the frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front cross-sectional view of an embodiment of a tubular positioning system. 
         FIG. 2A  is a side view of the system of  FIG. 1  located at an oilfield in a mobile fashion. 
         FIG. 2B  is a side view of the system of  FIG. 2A  with a lift frame thereof raised. 
         FIG. 2C  is a side view of the system of  FIG. 2B  with a trough thereof extended from the lift frame. 
         FIG. 3  is an overview of an oilfield accommodating the tubular positioning system of FIGS.  1  and  2 A- 2 C for delivery of a tubular therefrom to a rig floor. 
         FIG. 4  is a perspective view of the trough of the system of FIGS.  1  and  2 A- 2 C. 
         FIG. 5  is an exploded view of the interfacing of the undercarriage of the trough and the lift frame of FIGS.  1  and  2 A- 2 C. 
         FIG. 6  is a perspective view of an embodiment of a track for securing the trough and its undercarriage to the lift frame of FIGS.  1  and  2 A- 2 C. 
         FIG. 7  is a flow-chart summarizing an embodiment of employing a tubular positioning system for delivery of a tubular to a rig floor. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are described with reference to certain oilfield operations involving the delivery of certain specialty tubulars for well installation. For example, embodiments herein reference production tubing delivery and installation. However, other types of lighter weight tubular deliveries may take advantage of system embodiments and techniques detailed herein. For example, pipe and other completions tubulars may be delivered employing an embodiment of a system as described below. Regardless, embodiments of systems detailed herein employ a trough for extension from a lift frame in a sledding fashion so as to reduce replacement and repair costs where lighter weight tubulars are to be delivered to a rig floor. 
     Referring now to  FIG. 1 , a front cross-sectional view of an embodiment of a tubular positioning system  100  is shown. In the embodiment shown, the system  100  is configured with a trough  120  to accommodate a 20-40 foot tubular  110  of up to about 500 lbs. or more. Indeed, the tubular  110  depicted may be of such dimension and of between about 500 and 600 lbs., perhaps configured as a production tubular to ultimately transport production fluids through an inner channel  160  thereof. Given the comparatively lightweight nature of the types of tubulars accommodated, the system  100  itself may also be of a sufficiently lightweight nature to allow for mobile transport via a conventional trailer bed  175 . 
     Continuing with reference to  FIG. 1 , the trough  120  includes an undercarriage  140 . That is, the main body of the trough  120  is connected to an undercarriage  140  by way of feet  130  (see also  FIG. 2A-2C ). Further, the undercarriage  140  itself is made up of an internal beam  145  with outer polymer layer  147  to allow for a sledding interface  101  with a lift frame  150  as detailed further below. In the embodiment shown, the outer polymer layer  147  is in the form of a unitarily broad surface slider. However, the layer  147  may be provided as a narrower rail or runner. In fact, in an embodiment such as that depicted in  FIGS. 2C and 5 , the layer  147  may be provided in more discrete pad form. 
     Such sledding interface  101  may minimize variable movement between the frame  150  and the undercarriage  140  as the latter is extended as detailed further below. Thus, locations of focused high stress and wear at the interface  101  may be reduced as compared to a more conventional roller interface. Stated another way, the interface  101  may display a more even distribution between the frame  150  and undercarriage  140 . As such, operational efficiency and safety may also be enhanced. 
     The above noted trough  120  includes a metal structure  127  with a thick protective polymer layer  125  thereabove akin to commercial and non-commercial truck bed liners. For example, in one embodiment, the specialty tubular  110  may be a chrome alloy or otherwise particularly susceptible to damage during transport. Thus, the protective polymer layer  125  may serve to minimize such transport related damage to the tubular  110 . Indeed, delivery of the tubular  110  from a pipe rack adjacent the system  100  may be achieved by employment of conventional lifting arms that are also coated with such protective polymer layering for protection of the tubular  110 . 
     Referring now to  FIGS. 2A-2C  side views of the tubular positioning system  100  of  FIG. 1  are depicted at an oilfield  200 . More specifically, a mobile version of the system  100  is shown delivered to the oilfield  200  at  FIG. 2A  with the lift frame  150  hydraulically elevated at  FIG. 2B . Thus, extending of the undercarriage  140  and trough  120  may be employed to deliver a tubular  110  toward a rig floor  320  (see  FIG. 3 ). 
     With particular reference to  FIG. 2A , the system  100  is shown delivered to a location at the oilfield  200  via conventional hitch  220 . That is, as noted above a conventional lightweight 30 to 40 ft. trailer bed  175  may accommodate the system  100  due to the lighter weights involved as compared to more conventional casing and heavier weight tubular positioning systems. As shown in  FIG. 2A , the system  100  and trailer bed  175  are positioned and mobilized with perhaps about 4 to 10 conventional jack mounts  250 . Thus, subsequent elevating, extending and eventual tubular deployment may take place as the tubular  110  is directed to a well  380  running through an underlying formation  290  (see  FIG. 3 ). 
     With particular reference to  FIG. 2B , the lift frame  150  of the system  100  is shown elevated by hydraulic arms  275  disposed between the bed  175  and the frame  150 . That is, as the arms  275  are extended from the bed  175 , the frame  150  is rotated about a pivot joint  230  thereat. Thus, opposite the joint  230 , the frame  150  is raised upward, perhaps 10-40 feet or so above the trailer bed  175 . At this point it is worth noting that the trough  120  is equipped with a backstop  240 . Therefore, as the trough  120  is elevated at one end, the tubular  110  remains secured within the trough  120  at the other by way of this rear supporting backstop  240 . Once more, feet  130  extending below the trough  120  and to the undercarriage  140  help maintain stability thereof as the frame  150  is elevated. 
     Referring now to  FIG. 2C , a side view of the system  100  of  FIG. 2B  is depicted with the trough  120  being extended from the lift frame  150 . For example, the undercarriage  140  may be hydraulically extended out from the frame  150  in a sledding manner as noted above. More specifically, conventional hydraulics may be utilized to forcibly extend the trough  120  and undercarriage  140  as shown with the internal beam  145  sledding along its own polymer layers  147  as it emerges from the frame  150 . In the embodiment shown, the polymer layers  147  are provided in the form of discrete pads. However, as noted above, more broadly distributing rails, runners or sliders may be utilized. 
     Regardless the particular configuration of the polymer layers  147 , the sledding nature of the depicted telescopic boom is made practical by the lighter weight of the tubular  110  and overall system  100 , as compared to heavier casing positioning systems. Thus, a synthetic fluoropolymer such as conventional polytetrafluoroethylene (PTFE) may be robust enough for effective construction and use of the polymer layers  147  as described without undue concern over premature wear and failure. 
     Referring now to  FIG. 3 , an overview of an oilfield  200  is depicted which accommodates a well  380  traversing a formation. In the embodiment shown, the well  380  may be uncased but configured to accommodate production tubing in the form of the noted tubular  110 . Thus, the advantage of a mobile lighter weight tubular positioning system  100  may be quite significant given the lack of a need for any other heavier weight casing positioning system. In the embodiment shown, a mobile truck  300  is shown for system delivery which may be akin to lighter conventional trucks used for gooseneck injector or coiled tubing deliveries. In one embodiment, the truck  300  may be a conventional ¾ to one ton pickup. Of course, even where a heavier weight casing positioning system is initially employed, advantages of the depicted system  100  may be appreciated. 
     Continuing with reference to  FIG. 3 , a specialty tubular  110  has been rolled into a trough  120  which has been extended as detailed above. A boosting mechanism such as an elevator or strap  309  is then shown secured to a collar  210  of the tubular  110 . That is, once the tubular  110  is extended to within reach of a rig floor  320  of a rig  375  adjacent the system  100 , an operator may secure the strap  309  as indicated for removal of the tubular  110  from the trough  120 . More specifically, a pulley system  360  of the rig  375  may be utilized to draw up the tubular  110  via an elevator line  307 . 
     The tubular  110  may now be drawn up to a vertical orientation for eventually dropping down past a well head  340  and into the well  380 . In this manner, the tubular  110  may be coupled to other production tubulars  310  already disposed in the well  380 . Indeed, once complete, production from the well  380  may proceed through such tubular  310 ,  110  and out a production line  330  with operations directed by a control unit  350  disposed at the oilfield surface  200 . 
     With the fully extended trough  120  approaching the rig floor  320  in the manner shown, concern over dropping of the tubular  110  is minimized. For example, were the strap  309  to come loose or break as the tubular  110  is being removed, it would likely fall back into the trough  120  in a stable manner. 
     Referring now to  FIGS. 4-6 , different portions of the tubular positioning system  100  of  FIG. 1  are described in greater detail. More specifically, a perspective view of the trough  120  is shown in  FIG. 4  whereas more detailed features related to the interfacing of the undercarriage  140  with the lift frame  150  are highlighted in  FIGS. 5 and 6 . 
     With specific reference to  FIG. 4 , and additional reference to  FIGS. 1 and 3 , a perspective view of the trough  120  of the system  100  is depicted. As shown, the trough  120  is of an arcuate or concave shape configured to allow a tubular such as the production tubular  110  hereinabove to rest securely therein for transport to the rig floor  320 . Along these lines, given the potential specialty construction materials of the tubular  110 , the trough may include a protective polymer layer  125 . For example, in one the tubular  110  may be constructed at least partly of a chrome-based material. As such, the trough  120  may be of a supportive structural metal  127  that is coated with a sprayable polyurethane coating to serve as the protective polymer layer  125 . Thus, potential damage to the tubular  110  as a result of its own weight and transport may be largely minimized. 
     Referring now to  FIG. 5 , an exploded view of the interfacing of the undercarriage  140  with the lift frame  150  is depicted. In the embodiment shown, a discrete pad serves as the polymer layer  147  about the internal beam  145  of the undercarriage  140 . However, as noted above, this layer  147  may take a variety of different forms, including a broader slider-type embodiment or be provided in a more elongated or narrow rail-type form. Further, for illustration, the layer  147  is depicted about the beam  145  external the frame  150 . However, in an unexploded view such as that of  FIG. 1 , the layer  147 , in pad form or otherwise, would generally remain affixed to the inner surface  500  of the frame  150  during extension of the beam  145 . 
     Regardless, the layer  147  may be of a fluorocarbon such as polytetrafluoroethylene or other suitable non-stick material for allowing a sledding of the beam  145  along the inner surface  500  of the lift frame  150 . Such a sledding within the frame  150  may be particularly well suited for embodiments of the system where tubulars  110  such as that of  FIG. 1  are of less than about 1,000 lbs. Thus, weight based wear or failure of the layer  147  as a result of shearing during the sledding may be kept to a minimum. 
     Continuing with reference to  FIG. 5 , the sledding of the undercarriage  140  within the frame  150  may be controllably guided by the frame  150  itself. That is, in addition to a lower surface  503  over which the undercarriage  140  sleds, the frame  150  includes sidewalls  502 , and perhaps even upper lips  501 , to help guide the sledding. 
     Referring now to  FIG. 6 , a perspective view of an embodiment of a track  600  is shown at the upper portion of the lift frame  150 . In this view, the frame  150  is depicted from its rear or ‘pivot’ end, opposite that shown in  FIG. 1 . The track  600  is configured to provided added security to the trough  120  and its undercarriage  140  relative the lift frame  150 . That is, as the trough  120  and undercarriage  140  are sleddingly extended as depicted in  FIG. 2C , additional security and stability may be provided through the use of a track  600 . In the embodiment shown, the track  600  is incorporated into the frame  150  in a manner securing feet  130 , which emerge from below the trough  120 , as the noted sledding takes place. Thus, sufficient security between the trough  120  and frame  150  is ensured. Indeed, with added reference to  FIG. 3 , the likelihood of the trough  120  accidentally rolling or prematurely dropping a tubular  110  at the rig floor  320  is substantially eliminated. 
     In one embodiment, the depicted foot  130  may be slid rearward, extending out of the page in the depiction of  FIG. 6 , thereby exiting the confines of the track  600 . When this occurs, the trough  120  may lose a degree of stability relative the frame  150 . However, this may be intentionally advantageous. For example, in one embodiment, the rear end of the trough  120  may be configured to engage a receiver plate as the depicted foot  130  leaves the track  600 . In such an embodiment, the receiver plate may be configured to rotate the trough  120  relative the frame  150 , for example to controllably dump an unused tubular from the assembly. 
     Referring now to  FIG. 7 , a flow-chart is shown which summarizes an embodiment of employing a tubular positioning system for delivery of a tubular to a rig floor. Namely, a light weight or mobile tubular positioning system may be delivered to an oilfield along with a rack of tubular as indicated at  715  and  730 . Thus, a trough of the system may be loaded, one by one, with a tubulars from the rack as noted at  745 . 
     Once a tubular is loaded onto the trough an underlying lift frame may be raised as indicate at  760 . Thus, as indicated at  775 , extending of the trough from the frame may be undertaken in order to reach the vicinity of a rig floor at the oilfield. As such, the tubular may be removed from the trough as indicated at  790 . Perhaps more notably, however, the extending of the trough may be achieved in a sledding fashion. Thus, over time a substantial reduction in maintenance and equipment costs may be realized along with allowing for a lighter system with a greater degree of overall mobility. 
     The above described embodiments provide a smaller and lighter pickup machine for lighter weight specialty oilfield tubulars. Once more, equipment costs may be kept to about $100,000 in today&#39;s dollars without sacrifice of safety features such as stable trough delivery of tubulars. Perhaps most significantly, however, expenses associated with maintenance of the machine or ‘tubular positioning system’ may be dramatically reduced due to the elimination of a roller-based gantry. Thus, the ‘overkill’ provided by systems directed at heavier casing-type tubular delivery may be advantageously avoided. 
     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. Furthermore, 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.

Summary:
A system for delivering a downhole tubular from a rack at an oilfield surface to a rig floor thereat. The system includes a trough for accommodating the tubular that is slidably engaged with a lift frame in a sledded fashion. Thus, for delivery of the tubular, the trough may be sleddingly extended from the lift frame. That is, as opposed to a roller type of coupling between the trough and tubular, a sledded coupling is utilized that may require comparatively less maintenance and mobilization time. This may be particularly the case where lighter weight tubulars of less than about 1,000 lbs., preferably under about 500 lbs., are being delivered.