# Patent

## Title
Slickline conveyed bottom hole assembly with tractor

## Abstract

A bottom hole assembly is run into the wellbore on slickline with a tractor to assist in movement of the bottom hole assembly through a deviation in either direction. The tractor can have retractable drive components and can be responsive to tension in the slickline to turn it on and to avoid overrunning the slickline if driving out.

## Background
FIELD OF THE INVENTION
The field of this invention is tools run downhole preferably on cable and which operate with on board power to perform a downhole function and more particularly a combination of a bottom hole assembly with a tractor for driving in deviated wellbores.
BACKGROUND OF THE INVENTION
It is a common practice to plug wells and to have encroachment of water into the wellbore above the plug. FIG. 1 illustrates this phenomenon. It shows a wellbore 10 through formations 12, 14 and 16 with a plug 18 in zone 16. Water 20 has infiltrated as indicated by arrows 22 and brought sand 24 with it. There is not enough formation pressure to get the water 20 to the surface. As a result, the sand 24 simply settles on the plug 18.
There are many techniques developed to remove debris from wellbores and a good survey article that reviews many of these procedures is SPE 113267 Published June 2008 by Li, Misselbrook and Seal entitled Sand Cleanout with Coiled Tubing: Choice of Process, Tools or Fluids? There are limits to which techniques can be used with low pressure formations. Techniques that involve pressurized fluid circulation present risk of fluid loss into a low pressure formation from simply the fluid column hydrostatic pressure that is created when the well is filled with fluid and circulated or jetted. The productivity of the formation can be adversely affected should such flow into the formation occur. As an alternative to liquid circulation, systems involving foam have been proposed with the idea being that the density of the foam is so low that fluid losses will not be an issue. Instead, the foam entrains the sand or debris and carries it to the surface without the creation of a hydrostatic head on the low pressure formation in the vicinity of the plug. The downside of this technique is the cost of the specialized foam equipment and the logistics of getting such equipment to the well site in remote locations.
Various techniques of capturing debris have been developed. Some involve chambers that have flapper type valves that allow liquid and sand to enter and then use gravity to allow the flapper to close trapping in the sand. The motive force can be a chamber under vacuum that is opened to the collection chamber downhole or the use of a reciprocating pump with a series of flapper type check valves. These systems can have operational issues with sand buildup on the seats for the flappers that keep them from sealing and as a result some of the captured sand simply escapes again. Some of these one shot systems that depend on a vacuum chamber to suck in water and sand into a containment chamber have been run in on wireline. Illustrative of some of these debris cleanup devices are U.S. Pat. No. 6,196,319 (wireline); U.S. Pat. No. 5,327,974 (tubing run); U.S. Pat. No. 5,318,128 (tubing run); U.S. Pat. No. 6,607,607 (coiled tubing); U.S. Pat. No. 4,671,359 (coiled tubing); U.S. Pat. No. 6,464,012 (wireline); U.S. Pat. No. 4,924,940 (rigid tubing) and U.S. Pat. No. 6,059,030 (rigid tubing).
The reciprocation debris collection systems also have the issue of a lack of continuous flow which promotes entrained sand to drop when flow is interrupted. Another issue with some tools for debris removal is a minimum diameter for these tools keeps them from being used in very small diameter wells. Proper positioning is also an issue. With tools that trap sand from flow entering at the lower end and run in on coiled tubing there is a possibility of forcing the lower end into the sand where the manner of kicking on the pump involves setting down weight such as in U.S. Pat. No. 6,059,030. On the other hand, especially with the one shot vacuum tools, being too high in the water and well above the sand line will result in minimal capture of sand.
What is needed is a debris removal tool that can be quickly deployed such as by slickline and can be made small enough to be useful in small diameter wells while at the same time using a debris removal technique that features effective capture of the sand and preferably a continuous fluid circulation while doing so. A modular design can help with carrying capacity in small wells and save trips to the surface to remove the captured sand. Other features that maintain fluid velocity to keep the sand entrained and further employ centrifugal force in aid of separating the sand from the circulating fluid are also potential features of the present invention. Those skilled in the art will have a better idea of the various aspects of the invention from a review of the detailed description of the preferred embodiment and the associated drawings, while recognizing that the full scope of the invention is determined by the appended claims.
One of the issues with introduction of bottom hole assemblies into a wellbore is how to advance the assembly when the well is deviated to the point where the force of gravity is insufficient to assure further progress downhole. Various types of propulsion devices have been devised but are either not suited for slickline application or not adapted to advance a bottom hole assembly through a deviated well. Some examples of such designs are U.S. Pat. Nos. 7,392,859; 7,325,606; 7,152,680; 7,121,343; 6,945,330; 6,189,621 and 6,397,946. US Publication 2009/0045975 shows a tractor that is driven on a slickline where the slickline itself has been advanced into a wellbore by the force of gravity from the weight of the bottom hole assembly.
SUMMARY OF THE INVENTION
A bottom hole assembly is run into the wellbore on slickline with a tractor to assist in movement of the bottom hole assembly through a deviation in either direction. The tractor can have retractable drive components and can be responsive to tension in the slickline to turn it on and to avoid overrunning the slickline if driving out.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a section view of a plugged well where the debris collection device will be deployed;
FIG. 2 is the view of FIG. 1 with the device lowered into position adjacent the debris to be removed;
FIG. 3 is a detailed view of the debris removal device shown in FIG. 2;
FIG. 4 is a lower end view of the device in FIG. 3 and illustrating the modular capability of the design;
FIG. 5 is another application of a tool run on slickline to cut tubulars;
FIG. 6 is another application of a tool to scrape tubulars without an anchor that is run on slickline;
FIG. 7 is an alternative embodiment of the tool of FIG. 6 showing an anchoring feature used without the counter-rotating scrapers in FIG. 6;
FIG. 8 is a section view showing a slickline run tool used for moving a downhole component;
FIG. 9 is an alternative embodiment to the tool in FIG. 8 using a linear motor to set a packer;
FIG. 10 is an alternative to FIG. 9 that incorporates hydrostatic pressure to set a packer;
FIG. 11 illustrates the problem with using slicklines when encountering a wellbore that is deviated;
FIG. 12 illustrates how tractors are used to overcome the problem illustrated in FIG. 11;
FIG. 13 shows a tractor behind a bottom hole assembly where the tractor is not in the driving position;
FIG. 14 is the view of FIG. 13 with the tractor in the driving position;
FIG. 15 is an alternative driving device with retractable drive rollers shown in perspective;
FIG. 16 is a view of the linkage for the rollers of FIG. 15 in the retracted position;
FIG. 17 is the view of FIG. 16 in the rollers extended position;
FIG. 18 is a detailed view of the motor area in FIG. 15 showing the drive takeoffs;
FIG. 19 is an alternative embodiment of a fluid operated tractor; and
FIG. 20 is a detailed view of the tractor of FIG. 19.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 2 shows the tool 26 lowered into the water 20 on a slickline or non-conductive cable 28. The main features of the tool are a disconnect 30 at the lower end of the cable 28 and a control system 32 for turning the tool 26 on and off and for other purposes. A power supply, such as a battery 34, powers a motor 36, which in turn runs a pump 38. The modular debris removal tool 40 is at the bottom of the assembly.
While a cable or slickline 28 is preferred because it is a low cost way to rapidly get the tool 26 into the water 20, a wireline can also be used and surface power through the wireline can replace the onboard battery 34. The control system can be configured in different ways. In one version it can be a time delay energized at the surface so that the tool 26 will have enough time to be lowered into the water 20 before motor 36 starts running. Another way to actuate the motor 36 is to use a switch that is responsive to being immersed in water to complete the power delivery circuit. This can be a float type switch akin to a commode fill up valve or it can use the presence of water or other well fluids to otherwise complete a circuit. Since it is generally known at what depth the plug 18 has been set, the tool 26 can be quickly lowered to the approximate vicinity and then its speed reduced to avoid getting the lower end buried in the sand 24. The control system can also incorporate a flow switch to detect plugging in the debris tool 40 and shut the pump 38 to avoid ruining it or burning up the motor 36 if the pump 38 plugs up or stops turning for any reason. Other aspects of the control system 32 can include the ability to transmit electromagnetic or pressure wave signals through the wellbore or the slickline 28 such information such as the weight or volume of collected debris, for example.
Referring now to FIGS. 3 and 4, the inner details of the debris removal tool 40 are illustrated. There is a tapered inlet 50 leading to a preferably centered lift tube 52 that defines an annular volume 54 around it. Tube 52 can have one or more centrifugal separators 56 inside whose purpose is to get the fluid stream spinning to get the solids to the inner wall using centrifugal force. Alternatively, the tube 52 itself can be a spiral so that flow through it at a high enough velocity to keep the solids entrained will also cause them to migrate to the inner wall until the exit ports 58 are reached. Some of the sand or other debris will fall down in the annular volume 54 where the fluid velocity is low or non-existent. As best shown in FIG. 3, the fluid stream ultimately continues to a filter or screen 60 and into the suction of pump 38. The pump discharge exits at ports 62.
As shown in FIG. 4 the design can be modular so that tube 52 continues beyond partition 64 at thread 66 which defines a lowermost module. Thereafter, more modules can be added within the limits of the pump 38 to draw the required flow through tube 52. Each module has exit ports 58 that lead to a discrete annular volume 54 associated with each module. Additional modules increase the debris retention capacity and reduce the number of trips out of the well to remove the desired amount of sand 24.
Various options are contemplated. The tool 40 can be triggered to start when sensing the top of the layer of debris, or by depth in the well from known markers, or simply on a time delay basis. Movement uphole of a predetermined distance can shut the pump 38 off. This still allows the slickline operator to move up and down when reaching the debris so that he knows he is not stuck. The tool can include a vibrator to help fluidize the debris as an aid to getting it to move into the inlet 50. The pump 38 can be employed to also create vibration by eccentric mounting of its impeller. The pump can also be a turbine style or a progressive cavity type pump.
The tool 40 has the ability to provide continuous circulation which not only improves its debris removal capabilities but can also assist when running in or pulling out of the hole to reduce chances of getting the tool stuck.
While the preferred tool is a debris catcher, other tools can be run in on cable or slickline and have an on board power source for accomplishing other downhole operations. FIG. 2 is intended to schematically illustrate other tools 40 that can accomplish other tasks downhole such as honing or light milling. To the extent a torque is applied by the tool to accomplish the task, a part of the tool can also include an anchor portion to engage a well tubular to resist the torque applied by the tool 40. The slips or anchors that are used can be actuated with the on board power supply using a control system that for example can be responsive to a pattern of uphole and downhole movements of predetermined length to trigger the slips and start the tool.
FIG. 5 illustrates a tubular cutter 100 run in on slickline 102. On top is a control package 104 that is equipped to selectively start the cutter 100 at a given location that can be based on a stored well profile in a processor that is part of package 104. There can also be sensors that detect depth from markers in the well or there can more simply be a time delay with a surface estimation as to the depth needed for the cut. Sensors could be tactile feelers, spring loaded wheel counters or ultrasonic proximity sensors. A battery pack 106 supplies a motor 108 that turns a ball shaft 110 which in turn moves the hub 112 axially, in opposed directions. Movement of hub 112 rotates arms 114 that have a grip assembly 116 at an outer end for contact with the tubular 118 that is to be cut. A second motor 120 also driven by the battery pack 106 powers a gearbox 122 to slow its output speed. The gearbox 122 is connected to rotatably mounted housing 124 using gear 126. The gearbox 122 also turns ball screw 128 which drives housing 130 axially in opposed directions. Arms 132 and 134 link the housing 130 to the cutters 136. As arms 132 and 134 get closer to each other the cutters 136 extend radially. Reversing the rotational direction of cutter motor 120 retracts the cutters 136.
When the proper depth is reached and the anchor assemblies 116 get a firm grip on the tubular 118 to resist torque from cutting, the motor 120 is started to slowly extend the cutters 136 while the housing 124 is being driven by gear 126. When the cutters 136 engage the tubular 118 the cutting action begins. As the housing 124 rotates to cut the blades are slowly advanced radially into the tubular 118 to increase the depth of the cut. Controls can be added to regulate the cutting action. They controls can be as simple as providing fixed speeds for the housing 124 rotation and the cutter 136 extension so that the radial force on the cutter 136 will not stall the motor 120. Knowing the thickness of the tubular 118 the control package 104 can trigger the motor 120 to reverse when the cutters 136 have radially extended enough to cut through the tubular wall 118. Alternatively, the amount of axial movement of the housing 130 can be measured or the number of turns of the ball screw 128 can be measured by the control package 104 to detect when the tubular 118 should be cut all the way through. Other options can involve a sensor on the cutter 136 that can optically determine that the tubular 118 has been cut clean through. Reversing rotation on motors 108 and 120 will allow the cutters 136 to retract and the anchors 116 to retract for a fast trip out of the well using the slickline 102.
FIG. 6 illustrates a scraper tool 200 run on slickline 202 connected to a control package 204 that can in the same way as the package 104 discussed with regard to the FIG. 5 embodiment, selectively turn on the scraper 200 when the proper depth is reached. A battery pack 206 selectively powers the motor 208. Motor shaft 210 is linked to drum 212 for tandem rotation. A gear assembly 214 drives drum 216 in the opposite direction as drum 212. Each of the drums 212 and 216 have an array of flexible connectors 218 that each preferably have a ball 220 made of a hardened material such as carbide. There is a clearance around the extended balls 220 to the inner wall of the tubular 222 so that rotation can take place with side to side motion of the scraper 200 resulting in wall impacts on tubular 222 for the scraping action. There will be a minimal net torque force on the tool and it will not need to be anchored because the drums 212 and 216 rotate in opposite directions. In the alternative, there can be but a single drum 212 as shown in FIG. 7. In that case the tool 200 needs to be stabilized against the torque from the scraping action. One way to anchor the tool is to use selectively extendable bow springs 224 that are preferably retracted for run in with slickline 202 so that the tool can progress rapidly to the location that needs to be scraped. Other types of driven extendable anchors could also be used and powered to extend and retract with the battery pack 206. The scraper devices 220 can be made in a variety of shapes and include diamonds or other materials for the scraping action.
FIG. 8 shows a slickline 300 supporting a jar assembly 302 that is commonly employed with slicklines to use to release a tool that may get stuck in a wellbore and to indicate to the surface operator that the tool is in fact not stuck in its present location. The Jar assembly can also be used to shift a sleeve 310 when the shifting keys 322 are engaged to a profile 332. If an anchor is provided, the jar assembly 302 can be omitted and the motor 314 will actuate the sleeve 310. A sensor package 304 selectively completes a circuit powered by the batteries 306 to actuate the tool, which in this case is a sleeve shifting tool 308. The sensor package 304 can respond to locating collars or other signal transmitting devices 305 that indicate the approximate position of the sleeve 310 to be shifted to open or close the port 312. Alternatively the sensor package 304 can respond to a predetermined movement of the slickline 300 or the surrounding wellbore conditions or an electromagnetic or pressure wave, to name a few examples. The main purpose of the sensor package 304 is to preserve power in the batteries 306 by keeping electrical load off the battery when it is not needed. A motor 314 is powered by the batteries 306 and in turn rotates a ball screw 316, which, depending on the direction of motor rotation, makes the nut 318 move down against the bias of spring 320 or up with an assist from the spring 320 if the motor direction is reversed or the power to it is simply cut off. Fully open and fully closed and positions in between are possible for the sleeve 310 using the motor 314. The shifting keys 322 are supported by linkages 324 and 326 on opposed ends. As hub 328 moves toward hub 330 the shifting keys 322 move out radially and latch into a conforming pattern 322 in the shifting sleeve 310. There can be more than one sleeve 310 in the string 334 and it is preferred that the shifting pattern in each sleeve 310 be identical so that in one pass with the slickline 300 multiple sleeves can be opened or closed as needed regardless of their inside diameter. While a ball screw mechanism is illustrated in FIG. 8 other techniques for motor drivers such as a linear motor can be used to function equally.
FIG. 9 shows using a slickline 400 conveyed motor to set a mechanical packer 403. The tool 400 includes a disconnect 30, a battery 34, a control unit 401 and a motor unit 402. The motor unit can be a linear motor, a motor with a power screw or any other similar arrangements. When motor is actuated, the center piston or power screw 408 which is connected to the packer mandrel 410 moves respectively to the housing 409 against which it is braced to set the packer 403.
In another arrangement, as illustrated in FIG. 10, a tool such as a packer or a bridge plug is set by a slickline conveyed setting tool 430. The tool 430 also includes a disconnect 30, a battery 34, a control unit 401 and a motor unit 402. The motor unit 402 also can be a linear motor, a motor with a power screw or other similar arrangements. The center piston or power screw 411 is connected to a piston 404 which seals off using seals 405 a series of ports 412 at run in position. When the motor is actuated, the center piston or power screw 411 moves and allow the ports 412 to be connected to chamber 413. Hydrostatic pressure enters the chamber 413, working against atmosphere chamber 414, pushing down the setting piston 413 and moving an actuating rod 406. A tool 407 thus is set.
FIG. 11 illustrates a deviated wellbore 500 and a slickline 502 supporting a bottom hole assembly that can include logging tools or other tools 504. When the assembly 504 hits the deviation 506, forward progress stops and the cable goes slack as a signal on the surface that there is a problem downhole. When this happens, different steps have been taken to reduce friction such as adding external rollers or other bearings or adding viscosity reducers into the well. These systems have had limited success especially when the deviation is severe limiting the usefulness of the weight of the bottom hole assembly to further advance downhole.
FIG. 12 schematically illustrates the slickline 502 and the bottom hole assembly 504 but this time there is a tractor 508 that is connected to the bottom hole assembly (BHA) by a hinge or swivel joint or another connection 510. The tractor assembly 508 has onboard power that can drive wheels or tracks 512 selectively when the slickline 502 has a detected slack condition. Although the preferred location of the tractor assembly is ahead or downhole from the BHA 504 and on an end opposite from the slickline 502 placement of the tractor assembly 508 can also be on the uphole side of the BHA 504. At that time the drive system schematically represented by the tracks 512 starts up and drives the BHA 504 to the desired destination or until the deviation becomes slight enough to allow the slack to leave the slickline 502. If that happens the drive system 512 will shut down to conserve the power supply, which in the preferred embodiment will be onboard batteries. The connection 510 is articulated and is short enough to avoid binding in sharp turns but at the same time is flexible enough to allow the BHA 504 and the tractor 508 to go into different planes and to go over internal irregularities in the wellbore. It can be a plurality of ball and socket joints that can exhibit column strength in compression, which can occur when driving the BHA out of the wellbore as an assist to tension in the slickline. When coming out of the hole in the deviated section, the assembly 508 can be triggered to start so as to reduce the stress in the slickline 502 but to maintain a predetermined stress level to avoid overrunning the surface equipment and creating slack in the cable that can cause the cable 502 to ball up around the BHA 504. Ideally, a slight tension in the slickline 502 is desired when coming out of the hole. The mechanism that actually does the driving can be retractable to give the assembly 508 a smooth exterior profile where the well is not substantially deviated so that maximum advantage of the available gravitational force can be taken when tripping in the hole and to minimize the chances to getting stuck when tripping out. Apart from wheels 512 or a track system other driving alternatives are envisioned such a spiral on the exterior of a drum whose center axis is aligned with the assembly 508. Alternatively the tractor assembly can have a surrounding seal with an onboard pump that can pump fluid from one side of the seal to the opposite side of the seal and in so doing propel the assembly 508 in the desired direction. The drum can be solid or it can have articulated components to allow it to have a smaller diameter than the outer housing of the BHA 504 for when the driving is not required and a larger diameter to extend beyond the BHA 504 housing when it is required to drive the assembly 508. The drum can be driven in opposed direction depending on whether the BHA 504 is being tripped into and out of the well. The assembly 510 could have some column strength so that when tripping out of the well it can be in compression to provide a push force to the BHA 504 uphole such as to try to break it free if it gets stuck on the trip out of the hole. This objective can be addressed with a series of articulated links with limited degree of freedom to allow for some column strength and yet enough flexibility to flex to allow the assembly 508 to be in a different plane than the BHA 504. Such planes can intersect at up to 90 degrees. Different devices can be a part of the BHA 504 as discussed above. It should also be noted that relative rotation can be permitted between the assembly 508 and the BHA 504 which is permitted by the connector 510. This feature allows the assembly to negotiate a change of plane with a change in the deviation in the wellbore more easily in a deviated portion where the assembly 508 is operational.
FIG. 13 shows a tractor assembly 600 behind the bottom hole assembly 602 while being supported by a slickline 604. As in other embodiments, there is a drive motor 606 with an associated power supply such as a battery pack 608, for example, and a sensor system shown schematically as 610 that can detect stress in the slickline 604. If the well becomes deviated on the trip into the well the tension in the slickline 604 will decrease and the sensor 610 will actuate the tractor 600 to drive downhole while maintaining the slickline tension within targeted limits. On the way out of the hole if the tension increases beyond a given value, the tractor 600 will drive toward the surface to try to reduce the tension on the slickline 604 to within predetermined limits as surface personnel continue to apply some tension to remove the bottom hole assembly 602 while the tractor 600 tries to assist to a point where it will not overrun the slickline 604 so as to avoid getting tangled up in it. The way it does this is to stop driving if the slickline 604 tension decreases below a predetermined level.
The tractor assembly 600 has a continuous track 612 that rides on spring loaded idler sprockets 614 and 616 on the uphole end and 618 and 620 toward the downhole end. At the downhole point is spring loaded idler sprocket 622. Motor 606 drives the drive sprocket 624 at the uphole end. Hub 626 has pivoted links 628 and 630 that are biased apart by spring 632. Sprocket 614 is pivotally mounted at the end of link 630 and sprocket 616 is mounted at the end of link 628. Hub 634 has pivotally mounted links 636 and 638 that respectively have at their ends sprockets 618 and 620. A motorized ball screw assembly 640 is actuated by the sensor 610 to move hub 634 which articulates the links 636 and 638 away from each other and against the bias of return spring 642. The radially outward movement of sprockets 618 and 620 brings one part of the track 612 against the borehole wall 644. By virtue of links 646 and 648 the radial movement of sprockets 618 and 620 also cause radial movement of sprockets 614 and 616 against the track 612 to bring the uphole end of it against the borehole wall 644. In the FIG. 14 position driving uphole or downhole is then a function of the rotation direction of the drive motor 606 turning the drive sprocket 624. When ball screw assembly 640 is run in the reverse direction the FIG. 13 position is resumed and the tractor 600 no longer drives the bottom hole assembly 602. Those skilled in the art will recognize that the positions of the tractor 600 and the bottom hole assembly 602 can be reversed. In either configuration the orientation of the tractor assembly 600 can be as shown or flipped 180 degrees.
FIGS. 15-18 is a different driving configuration using retractable driven rollers that have an exterior screw profile and which can be driven in opposed directions for movement into or out of the wellbore. A housing 700 has multiple openings 702 through which rollers 704 are selectively extendable and driven to rotate on their own axis 706 so that the spiral or screw grooved patterns 708 can engage the borehole wall (not shown) to selectively drive the housing 700 in opposed directions as needed. This embodiment has a motor 710 as well as a power supply and sensors that are not shown that work in a similar manner as other described embodiments. Motor 710 has a drive shaft 712 that has three drive takeoffs 714, 716 and 718 that respectively follow links 720, 722 and 724 as shown in FIG. 17. Those three links are respectively pivotally mounted to three outer links 726, 728 and 730 with each of the latter having a roller 704 pivotally mounted at an outboard end. The three outer links are pivotally mounted at pins 732, 734 and 736 respectively. Drives 714, 716 and 718 respectively continue as drives 738, 740 and 742 to the respective rollers 704 to drive them on their own axes 706. There is a second motor 744 whose purpose is to rotate hub 746 a predetermined angular amount which in turn rotates links 720, 722 and 724 a predetermined amount which in turn rotates links 726, 728 and 730 about their respective pinned mountings 732, 734 and 736 to extend or retract the rollers 704 while motor 710 drives the rollers 704 on their axes 706 in the manner previously described. The grooved and spiraled pattern 708 gets a grip on the wellbore wall while the motor 744 is finely adjusted to keep the requisite amount of surface contact with the wellbore wall by the rollers 704 without having them so tight on the wellbore wall as to impede their rotation on their own axes 706 so that the spiraled pattern simply winds up digging into the wellbore wall rather than driving the bottom hole assembly along the wellbore wall. In other respects the control of this embodiment of the drive system is the same as in other embodiments.
FIGS. 19 and 20 show another form of propulsion for a bottom hole assembly 800 having a fluid drive assembly 802 mounted adjacent to it. As in the other embodiments, there are a motor 804, a power supply preferably batteries 806 and a sensor assembly 808 to detect slickline 810 tension and to regulate the operation of the centrifugal pump 812. The drive housing 814 has inlet ports 816 to the pump 812. A series of outlets 818 are on a bottom of the housing 814. These outlets can be fixed or variable so that the direction of the exhausted fluid can be changed for driving the housing uphole or downhole or simply fluidizing the housing 814 by lifting it of the hole bottom in a deviated portion to allow the force of gravity to get the bottom hole assembly 800 to go downhole if the deviation is not too severe. One or more outlets 820 from the pump 812 can be directed axially along the top of the housing 814 to help keep it centered in conjunction with the array of nozzles 818. The nozzles 818 can be articulated with a sleeve that has the same hole pattern as the nozzle outlets to change the relative alignment between overlapping hole patterns so that rather than simply fluidizing the direction of the fluid jets can created propulsion in the uphole or the downhole directions for the bottom hole assembly 800.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:

## Claims

1. A tractor assembly for moving a bottom hole assembly in a subterranean location, comprising:
a bottom hole assembly supported by a slickline;
a tractor connected to said bottom hole assembly, said tractor further comprising a power supply for selective assistance to bottom hole assembly movement in the subterranean location;
said tractor further comprises a control system to sense reduction in tension in said slickline which indicates a potential for slack in said slickline to drive said tractor to move the bottom hole assembly in a direction that increases said tension and avoids a slack condition that can make said bottom hole assembly get stuck at a subterranean location.

2. The tractor assembly of claim 1, wherein:
said tractor and said slickline are connected on opposite sides of said bottom hole assembly.

3. The tractor assembly of claim 1, wherein:
said tractor is located on the same side of the bottom hole assembly connection as said slickline.

4. The tractor assembly of claim 1, wherein:
said tractor drives said bottom hole assembly in opposed directions.

5. The tractor assembly of claim 4, wherein:
said tractor is selectively operated in response to a predetermined tension in said slickline.

6. The tractor assembly of claim 5, wherein:
said tractor further comprises a control system to sense reduction of tension in said slickline while said tractor is driving and to slow or stop said tractor minimize or prevent the bottom hole assembly from running over said slickline.

7. The tractor assembly of claim 1, wherein:
said tractor is connected to said bottom hole assembly with a flexible connection.

8. The tractor assembly of claim 7, wherein:
said flexible connection transmits force in compression.

9. The tractor assembly of claim 7, wherein:
said flexible connection allows the bottom hole assembly and the tractor to be oriented at different angles or to be disposed in different planes.

10. The tractor assembly of claim 1, wherein:
said tractor comprises a retractable drive mechanism movable toward and away from said body of said tractor.

11. The tractor assembly of claim 10, wherein:
said retractable drive retracts so that said retractable drive does not extend beyond an outer dimension of said housing.

12. The tractor assembly of claim 1, wherein:
said tractor comprises a drive mechanism that further comprises wheels, at least one track or driven rollers with an exterior extending spiral configuration.

13. The tractor assembly of claim 12, wherein:
said track is actuated radially for driving by linkage mounted sprockets actuated by a positioning motor while a separate drive motor turns a driving sprocket engaged to said track.

14. The tractor assembly of claim 13, wherein:
said positioning motor comprises a shaft driven by a ball screw.

15. The tractor assembly of claim 1, wherein:
said tractor comprises a drive mechanism using a peripheral seal in the wellbore and an onboard pump to move well fluid from one side of said seal to the other to propel said tractor.

16. The tractor assembly of claim 1, wherein:
said tractor further comprises a control system to selectively use power from said power supply responsive to a supplied signal.

17. The tractor assembly of claim 1, wherein:
said tractor uses fluid force exiting through openings to drive said bottom hole assembly.

18. The tractor assembly of claim 1, wherein:
said tractor uses fluid force exiting through openings to fluidize said bottom hole assembly.

19. The tractor assembly of claim 17, wherein:
the orientation of said openings is variable for driving said bottom hole assembly in opposed directions.

20. A tractor assembly for moving a bottom hole assembly in a subterranean location, comprising:
a bottom hole assembly supported by a slickline;
a tractor connected to said bottom hole assembly, said tractor further comprising a power supply for selective assistance to bottom hole assembly movement in the subterranean location;
said tractor comprises a drive mechanism that further comprises wheels, at least one track or driven rollers with an exterior extending spiral configuration;
said wheels, track or rollers are retracted and extended by a linkage actuated by a first motor for maintaining contact pressure with the wellbore and said wheels, track or rollers are driven by a second motor using a drive system that articulates with said linkage.