A tool for multiple purposes features one ore more dogs that can engage a collar groove or restriction sub in the wellbore. The dogs are extendable through a sleeve biased in opposed directions and are supported from a mandrel. The dogs can retract into mandrel grooves to clear restrictions on the trip into the well. On the way up to a collar that has just been passed, the dogs engage and an upward pull on the mandrel displaces fluid through a restriction to allow enough time to get a meaningful surface signal of the overpull force. Thereafter, the applied force can be reduced as the dogs release at a lower applied force to reduce the slingshot effect. The tool can be inverted and used to keep a constant force on a bottom hole assembly during offshore drilling where a heave compensator is employed.

FIELD OF THE INVENTION 
     The field of this invention is devices that can be used downhole to locate collars and/or other features in the wellbore and give a surface signal of such location or in a reverse orientation can be used to apply a predetermined load on a bottom hole assembly (BHA). 
     BACKGROUND OF THE INVENTION 
     Frequently the specific depth of collars and/or other features in the wellbore in a casing string needs to be located with an indication at the surface that the collar has been properly located. In the past this function has been approached with a tool delivered on a string that has one or more collets. The collets and the mandrel that backs them up are configured to allow the collets to remain in an unsupported position for downhole tripping. After the desired collar is reached the tool with the collets is further advanced downhole beyond a locating groove in the collar that is of interest. The tool is then picked back up to engage the collar. Doing this traps the collet in the groove and an overpull is applied. The resistance to the overpull is sensed at the surface. The collet is designed to release after a predetermined level of pulling force is reached. 
     There are several issues with this design. In deep wells with a significant amount of deviation there is a substantial risk of drag of the work string in the surrounding tubular so that the overpull applied could be the force required to dislodge the work string as opposed to a pull on the collets that may not even have landed in the locator groove of the collar in question. This drag effect induced by depth and well deviation is commonly referred to as a “slip/stick effect”. There may be no ascertainable signal at the surface if the slip/stick effect is present. Another problem is the limit of stress that can be applied to the collet heads that are in the locating groove. While the collet structure can be made thicker the problem there is that the material may be limited in the level of stress that can be endured on the trapped collet heads. Another issue is limited space and tool diameter restriction required to actually deliver the tool to the collar in interest. Thus making the parts thicker may not be sufficiently helpful to increase the overall rating toward the desired pulling force required or there may not be the room required to go this route. Another issue with the collet based systems is that upon release there is a slingshot effect as the stored potential energy in the applied pulling force on the work string is suddenly released as the collets become unsupported when a predetermined pulling force is reached. 
     Accordingly what is needed and is addressed by the present invention is a tool that can handle greater applied forces than the collet based designs and on that can eliminate the slingshot effect. Other desirable features can be a built in delay that allows higher loads to be applied for a defined time period to be sure that the collar is properly located and that the slip/stick forces have been overcome. A rapid re-cocking of the tool after a release for repeated testing is also a feature. The tool can be inverted and properly regulated so as to apply a predetermined downward force on a bottom hole assembly working in conjunction with a heave compensator for offshore drilling applications. These and other features of the present invention will become more apparent to those skilled in the art from a review of the description of the preferred embodiment, the drawings and the claims that determine the scope of the invention, all of which appear below. 
     SUMMARY OF THE INVENTION 
     A tool for multiple purposes features one ore more dogs that can engage a collar groove or restriction sub in the wellbore. The dogs are extendable through a sleeve biased in opposed directions and are supported from a mandrel. The dogs can retract into mandrel grooves to clear restrictions on the trip into the well. On the way up to a collar that has just been passed, the dogs engage and an upward pull on the mandrel displaces fluid through a restriction to allow enough time to get a meaningful surface signal of the overpull force. Thereafter, the applied force can be reduced as the dogs release at a lower applied force to reduce the slingshot effect. The tool can be inverted and used to keep a constant force on a bottom hole assembly during offshore drilling where a heave compensator is employed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a - 1   b  show the tool in section in the neutral run in position; 
         FIGS. 2   a - 2   b  show the tool in section in the position for clearing an obstacle on run in; 
         FIGS. 3   a - 3   b  show the tool is section in the load applied position just prior to release; 
         FIG. 4  is a section along lines  4 - 4  of  FIG. 1   b ; and 
         FIG. 5  is a section view along lines  5 - 5  of  FIG. 1   a.    
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The mandrel  10  is made up of top sub  12 , upper body  14 , lower body  16  and bottom sub  18 . These pieces are preferably threaded together but may be attached in other ways. More or fewer pieces can be used to define the mandrel  10 . An outer sleeve  20  has a window  22  for each dog  24  that is used. One or more dogs  24  can be used. Dogs  24  have tabs  26  at opposed ends, as best seen in  FIG. 5  to limit the outward travel of the dogs  24  with respect to window  22 .  FIG. 1   a  shows the dog  24  in section. In the preferred form of dog  24 , it is generally U-shaped having a pair of inwardly oriented legs  28  and  30 . On the trip into the well surface  32  on dog  24  will encounter an obstacle. On the trip out of the well, surface  34  on dog  24  will encounter an obstacle. 
     Sleeve  20  is mounted to slide over mandrel  10 . It is biased uphole by spring  36  that bears on surface  38  of bottom sub  18 . Spring  40  bears on surface  42  of top sub  12  and applies an opposing force to sleeve  20  than spring  36 . Preferably spring  40  is weaker than spring  36  for reasons that will be explained below. 
     Upper body  14  has three grooves  44 ,  46 , and  48 . These grooves are deep enough so that when legs  28  and  30  are in them, outer surface  50  of dogs  24  recedes inside of window  22 . In this manner the tool can pass an obstruction going downhole and can be removed after release going uphole. If an obstruction is encountered by surface  32  going in the hole, the spring  40  is compressed as the sleeve  20  and dogs  24  stop downhole motion. Continued downhole movement of mandrel  10  not only compresses spring  40  but also positions grooves  44  and  46  in alignment with legs  28  and  30  of dogs  24  to allow them to retract to a position closer to the central axis  52  and preferably within sleeve  20 . At that point the obstruction can be passed and spring  40  can bias the sleeve  20  back into the neutral position shown in  FIG. 1 .  FIG. 2  shows the legs  28  and  30  getting cammed out of grooves  44  and  46  by the action of spring  40  after the obstruction going downhole is cleared. Note that sloping surfaces  52  and  54  facilitate the exit of legs  28  and  30  from grooves  44  and  46  under the return force of the formerly compressed spring  40 . With the obstacle cleared going downhole, the dogs  24  resume the neutral run in position shown in  FIG. 1 . 
     Defined between the sleeve  20  and the mandrel  10  and best seen in  FIG. 3  are an upper fluid reservoir  56  and a lower fluid reservoir  58 . A fill port  60  allows charging the fluid at the surface. Thermal and hydrostatic effects in this closed system of interconnected reservoirs are fully compensated by a piston  62  that can be biased by Belleville washers  64 , for example, or any other device that is comparable. Those skilled in the art will appreciate the benefit of such compensation on the structure of the device especially when it is deployed at great depths and/or high temperature applications.  FIG. 4  illustrates this execution of a compensation feature.  FIG. 2   b  best illustrates other features of this reservoir system. There is a flow restrictor  66  that regulates the flow rate from reservoir  58  into reservoir  56 . There is a check valve  68  that permits a bypass of restrictor  66  when the fluid is flowing in the opposite direction from reservoir  56  to reservoir  58 . A pressure relief device  70  is in line with the restrictor  66  so that when fluid is urged in a direction from reservoir  58  to reservoir  56  there will have to be a rise in the driving pressure to cause such flow to a predetermined level before any flow begins. 
     Broadly stated, the fluid system is operative to create a delay as the dogs  24  are in the desired location and a force is applied to the mandrel  10  to create a surface signal for such engagement prior to the release of the dogs  24  from the locating groove (not shown). The system serves to allow a reduction of the applied pulling force before release to reduce the slingshot effect from release. When used with the optional pressure relief device  70  the tool can be inverted and can be used to apply a load in a predetermined range on a BHA without concern for premature release, such as an offshore drilling application where a heave compensator system is employed. 
     Now that the main components have been described, the operation of the tool in various applications will be discussed in more detail.  FIG. 1  shows the run in position with the dogs  24  having legs  28  and  30  out of any of the grooves  44 ,  46  and  48 . Preferably, the dogs  24  are biased into the  FIG. 1  position where legs  28  and  30  straddle groove  46  by virtue of spring  36  overpowering spring  40  to move sleeve  20  to the  FIG. 1  position. As the tool is brought downhole, an obstacle will first hit surface  32  on dogs  24 . The mandrel  10  will continue downhole as the dogs  24  stop the descent of the sleeve  20 . As grooves  44  and  46  come into alignment with legs  28  and  30 , the dogs  24  will be able to retract sufficiently to allow the tool to continue past the obstacle. The dogs  24  can retract within sleeve  20  as much as necessary to allow the obstacle to be cleared. The advancing of the mandrel  10  with the dogs  24  temporarily stuck on an obstacle, compresses spring  40 . After the obstacle is cleared, spring  40  relaxes to return the tool to the  FIG. 1  position from the  FIG. 2  position. It should be noted that advancing the mandrel downhole with the dogs  24  stopped by an obstacle will result in sleeve  20  taking dogs  24  against the bias of spring  40  taking the lower end  21  of sleeve  20  away from upper end  23  of sleeve  25 , whose relative movement with respect to the mandrel  10 , at other times, creates movement of fluid between reservoirs  56  and  58 . The amount of this movement to reset the dogs  24  to the  FIG. 1  position after clearing the obstacle is also quite short. 
     When the desired depth is reached, the tool is pulled up until the surface  34  engages a desired locating groove downhole. At that point, further upward pulling on the mandrel  10  from the work string (not shown) will force fluid from reservoir  58  to reservoir  56  through restrictor  66 . This regulates the rate of movement of mandrel  10  as the force is being applied to give surface personnel the time to notice a signal that the desired groove has been engaged and a force that well exceeds the potential drag force from friction of slip/stick effects on the work string in a deviated wellbore are applied. The rig crew can then actually lower the applied pulling force before the actual release happens to reduce the slingshot effect from the release. Release occurs after the mandrel  10  moves a sufficient distance to place grooves  46  and  48  in alignment with legs  28  and  30  to allow the dogs  24  to retract and the tool to be returned to the  FIG. 1  position. This occurs because the pulling uphole with the dogs  24  in the locating groove compresses spring  36  as seen in  FIG. 3 . Retraction of the dogs  24  allows spring  36  to overcome spring  40  and the tool returns to the  FIG. 1  position, ready for another cycle. With the use of the optional relief device  70  the surface personnel are assured that a pulling force up to a predetermined level will not initiate the release sequence. Hence force can be applied and removed any number of times before there is a release. Those skilled in the art will appreciate that the tool can be used in an inverted orientation and function similarly in one application, for example where a range of weight on a BHA is desired in a given range without fear of initiating a release sequence. In such an application, rather than a pulling force uphole, a pushing force downhole is applied with the dogs  24  engaged in a receptacle. Combining with the use of the optional relief device  70  no fluid flow between reservoirs  56  and  58  can happen until a predetermined force is exceeded. This configuration can be used in offshore drilling in conjunction with heave compensators. 
     Those skilled in the art will now appreciate that the described tool can allow applied forces in the order of 100,000 or more where the collet designs were more limited to lower applied forces in the order of 40,000 pounds or less. These lower limits on the collet designs were sometimes not sufficient to exceed friction and slip/stick effects on the work string in highly deviated holes. The use of a dog structure extending through a window and more specifically a dog design having thick upper and lower ends using legs  28  and  30  accounts at least in part for the ability to apply higher forces to clear obstacles and to test the location of the tool in a desired groove in a specific collar, for example. The use of the check valve  68  allows the tool to quickly find its neutral position after a release so that the test can be quickly repeated, if desired. The use of the restrictor  66  allows more time at the surface to hold a force before release and further allows lowering the applied force after the passage of time but before release to reduce the slingshot effect from release. The pressure relief device  70  allows application of force for any desired time without fear of release if the force is kept at a level where the relief device remains closed. The fluid used on the reservoirs can be a liquid or gas. The compensator  62  is an optional feature. The tool is serviceable in the well in opposed orientations depending on the intended service. Although 4 dogs  24  are illustrated one or more such dogs can be used. Biasing of springs  36  and  40  can be accomplished by equivalent devices. 
     While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the exemplified embodiments set forth herein but is to be limited only by the scope of the attached claims, including the full range of equivalency to which each element thereof is entitled.