Abstract:
A linkage device separate from the integrated slips bridge links the pair of spaced-apart members of each slip to prevent sizeable fractured bits from moving away in the event of a fracture in the slip. The linkage device comprises a pair of ductile steel bars the ends of which loosely anchor in holes in each slip member, the holes being located at both sides of the slips at opposite ends of a groove that houses the linkage bar preventing it from falling out of the holes. In this way, a fractured slip may continue to assist in setting the tool and, moreover, potential hazardous interference in further tool operations are avoided. Furthermore, tool damage including slips fracture is reduced by a resilient damper material which buffers the lower cone as it slides down on the slip-holder cage during a tool release operation.

Description:
PRIOR RELATED APPLICATIONS 
     This patent application claims the benefit of the priority of Argentine patent application serial number P100104972 filed on 28 Dec. 2010. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO SEQUENCE LISTING, A TABLE OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns tools for borehole applications, in particular oil wells, gas wells or water-wells, more particularly including installations for primary, secondary or tertiary oil production, whether holes for injecting water, gas or another pressurizing agent (injector holes) or oil extraction (production wells). A particular application of the tool is in injector and producer multi-zone wells where the number of isolation zones is high and/or the wellbore casing is damaged or diverted, to quickly and economically isolate areas with damaged casing. 
     The present invention applies to tools carrying a packer device comprising seals mounted to a mandrel and forming with other operational components a tubing string (or just “tubing”) of tools and components joined one after another for lowering down a multifunctional (or multizonal) well, i.e., having multiple layers or strata which should be isolated from one another. Packer tools are not unusual in the oil industry. The tubing string comprising a number of function-specific tools is lowered into a well, maintaining an annular space between and a well casing. 
     Packer tools generally comprise two basic elements: packer seals for isolating annular regions thereabove and below and anchor slips to affix the tool to a point of the casing. A packer sealing element is a ring made of metal and typically dense synthetic rubber that fits around the tubing in a well. The packer seal (the “packing element”) of a packer tool (the “packer”) is typically a rubber ring that expands against the side of the casing lining the side of the wellbore. A packer may, and usually will, have more than one packing element. In the majority of active wells in the world today, this tubing is used to either produce oil or gas out of the well and serve as a conduit to transport water into the well for water injection and water flood applications. The packer provides a secure packer seal between everything above and below where it is set. The main reasons for using a packer are to keep sediment, sand and other potentially corrosive or erosive materials from flowing into the annulus and damaging the casing, and to control the zone of the well from which hydrocarbons are being produced in a producer well or to control the zone where water is being injected in an injection well. 
     Slips hold the packer in place and prevent them from moving once they are set in the well. A slip is a serrated piece of metal that grips the side of the casing. Some packers lack a specific anchor device (in which case they are known as packer-tandems). 
     Insofar the present invention, the packer tool sequentially carries out the following phases: 
     Run-in: The tubing enters the well and the packer is lowered down to a set position. 
     Setting: Both the anchor slips and the packer seals are pushed outwards to respectively clamp the tool to the well during all the time the tubing stays down the well and isolate annular regions above and below the packer. The tool setting system may be mechanical, involving rotation or axial compression or traction, or else hydraulic by injecting a pressurizing fluid. 
     Release: This operation is carried out on removable tools to unset them from the well casing in order that they may be extracted. In tools having release systems, known as removable packers, release may be based on similar maneuvers or a combination thereof. Tools lacking a release system are known as permanent packers which need to be rotated to literally destroy the tool by machine milling. This operation is costly and time-consuming. 
     Extraction: The removable packer is hauled up to the mouth of the well. 
     The invention particularly relates to a packer tool that is removable, hydraulically set and mechanically released. 
     The present invention concerns the packer tool anchor means to the well casing wall by means of a dual-grip anchor device having bidirectional anchor slips, more precisely, the structural integrity of the anchor slips. 
     Use of mechanically- or hydraulically-actuated packer tools or, simply, packers for maintaining separation between production layers or fluid injection layers is well known in the oil industry. 
     The best known release systems are by rotation and traction. In the first system, the tool is released by rotating it several turns, which complicates the operation the deeper the well because of the greater number of tools. This in turn makes the operation unreliable through uncertainty regarding which tool is actually being operated. 
     In traction release, tractive tension is applied to the piping to shear a number of brass or steel pins. Once set, this kind of tool is subject to stress from temperature and pressure variations down the well, which get worse with increased depth to the point that pins may shear producing accidental tool release. 
     Also known in the art is to provide packer tools with an anchor device to affix the tool to the well casing wall for the duration in which the tool will remain inside the well for operations. U.S. Pat. No. 4,156,460 discloses a removable packer with two sets of separate sets of slips teeth with a seal device in between. Each set comprises four anchor slips at 90° from one another around mandrel. The upper set has its teeth facing upwards to selectively anchor the tool against upwardly movement whereas the teeth of the lower anchor slips face down in the opposite direction to selectively hold the tool against downwardly movement. Each set is engaged by its own actuator cone. 
     CA patent 2,286,957 illustrates the known concept of integrating the teeth of anchor slips in pairs, each pair consisting of one set of teeth directed against upward movement and another set of teeth directed against movement downwards, arranged side-by-side as a unit on a single piece, forming four anchor slips pieces which protrude through respective rectangular windows cut out in a cage, so as to share a single actuator cone. Moreover, this &#39;957 CA patent suggests arranging the anchor slips at opposite ends of each anchor unit such that each anchor piece comprises an upper teeth member and a lower teeth member rigidly joined by a bridge forming part of the same unit. 
     This arrangement, which is also adopted in my prior AR patent publication 53,432 A1, is currently preferred and used in the present invention since it simplifies construction and operations. However, since the components of these types of tools frequently operate in extreme mechanical and thermal conditions, the anchor slips units are not free from becoming fractured during the tool run-in and dwelling time down a well. 
     The fracture of an anchor slip, aside from meaning potential problems for setting the tool, may also produce metal bits and pieces which may interfere with the movement of tool members such as during release operations and jam tool recovery. Pieces having substantial sizes may break off from the slips. The chance that a broken piece may interfere or jam an operation increases with the size of the broken-off piece. Slips fractures may occur near the bridge of the slips unit where the material properties transition, such that sizeable pieces or even an entire member may break off. 
     Furthermore, anchor slips may suffer damage in a well when beginning a release operation by turning the tool so that the release cone moves downwards to make room for the anchor slips to retract. Cone descent follows rotation of snugs formed on the mandrel that were retaining cone in its initial position and may be violent since it is driven by the weight of the cone itself, that of the lower sub depending from the cone and, more importantly, the load of the lower tubing components hanging from the lower sub of the tool. 
     The short and fast descent of the cone ends abruptly when a step thereof strikes a step formed at the bottom of the cage. The subsequent jar is transmitted to the anchor slips in the same and may fracture them. 
     Slips fracture causes randomly sized bits and pieces to come apart. Such broken pieces may get wedged in the annular space between the casing and some part of the tool such as the casing, troubling later attempts to haul the tool up, or fall inwards making release incomplete. 
     AR patent publication 41,393 (Reumann) discloses using an elastic means as a damper in a tool having a packing-holder collar and a wedge-shaped slips piece. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the invention is to provide a packer applicable to tools with dual-slips and hydraulic setting to overcome the above-mentioned prior art problems, thereby providing a packer having simple and reliable setting and release systems, converting it into a highly desirable tool for installations with multiple packers, useful for selective water injection, selective oil production or gas lift. 
     A particular object of the invention is to reduce the probability that an anchor slip may fracture as a result of jarring of the cage mounting the slips and, what could be more important still, in the event that a slip should break, reduce the probability that bits that have broken off and become separated from the main slip piece may interfere with operations for releasing the tool or extracting the tool from a well. A further object is to enhance the capacity of a fractured slip to carry out an anchor function. 
     The present invention overcomes the problem of fractured slip bits breaking off and separating by means of a linkage device which is separate from the bridge integrated with the slip. The separate linkage device links the pair of spaced-apart slip members to keep them together in the event of a fracture of a substantial part of the slip. This safety system against fractures provides more reliability to setting the tool since it means that the fractured bits will not move apart but will assist in anchoring the slips to the casing. 
     The linkage device is preferably embodied by a pair of stainless steel bars which are each lodged in a respective groove formed in the opposite sidewall of the slip. The ends of the bars are bent at right-angles and loosely anchored in blind holes formed in each slip member, the grooves extending from one blind hole to the other. In the event that a sizeable bit of a slip member should fracture, the fractured bit remains anchored by the linkage bars, thereby staying in place. Although in such an event it is foreseeable that the setting capacity of the fractured slip will not be the same, in any case some grip capacity to the casing may be provided in this way with this low cost solution of simple construction which, furthermore, prevents timely and costly problems when the time comes to release the anchor slips and raise the tool up and out of the well. 
     According to another aspect, the present invention reduces the intensity of the jarring to which the slips-holder cage is subjected to on account of it being met by the lower cone travelling downwards at the beginning of the release process. This is achieved, and potential damage to the anchor slips avoided, by inserting a resilient material to form a buffer between two complementary steps respectively protruding from the lower cone and the cage to dampen the effect of the free-falling cone hitting the cage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings help to convey features of the present invention and advantages thereof by means of a preferred embodiment. In the drawings: 
         FIG. 1A  is a view half elevation and half axial-section of a preferred embodiment of a packer tool according to the present invention, in an initial position ready for run-in; 
         FIG. 1B  is a view analogous to  FIG. 1A  but with the tool in the set position; 
         FIG. 1C  is a view analogous to  FIGS. 1A and 1B  but with the tool in the released position, ready for extraction, after its mandrel has turned 60°; 
         FIG. 2A  is a magnified half-axial section view of the hydraulic mechanism of the packer tool of  FIG. 1A  with its chamber, piston and cylinder in the initial position for run-in; 
         FIG. 2B  is a magnified view analogous to  FIG. 2A  but wherein the safety device guarding against premature setting has been disabled during the transition to setting the tool; 
         FIG. 2C  is a magnified view analogous to  FIGS. 2A and 2B  but wherein the hydraulic mechanism has reached the final setting position and is stable; 
         FIG. 3A  is a magnified half-axial section view of the packing mechanism of the packer tool of  FIG. 1A  in the initial run-in position; 
         FIG. 3B  is a magnified view analogous to  FIG. 3A  except that the packing mechanism is now in the set position; 
         FIG. 3C  is a magnified view analogous to  FIGS. 3A and 3B  but wherein the mandrel has been turned 60° to release the packing mechanism; 
         FIG. 4A  is a magnified half-axial section view of the anchor mechanism of the packer tool of  FIG. 1A  in the initial run-in position; 
         FIG. 4B  is a magnified view analogous to  FIG. 3A  except that the anchor mechanism is now in the set position; 
         FIG. 4C  is a magnified view analogous to  FIGS. 3A and 3B  but wherein the mandrel has been turned 60° as in  FIG. 3C  to release the anchor mechanism; 
         FIG. 5A  is a perspective view of the hydraulic mechanism of the tool of  FIG. 2A  wherein a quadrant of the view has been removed to show the annular segments of the antisetting mechanism in place in their initial position; 
         FIG. 5B  is a perspective view analogous to  FIG. 5A  of the hydraulic mechanism of  FIG. 2B  showing relocation of the annular segments when setting is activated; 
         FIG. 6A  shows the circumferential distribution of the annular segments which make up the antisetting safety mechanism of  FIGS. 2 and 5  (alphabetic suffices are omitted from figure and reference numbers in the present description to indicate generalization), wherein some components such as O-rings have been omitted for the sake of clarity; 
         FIG. 6B  is a cross-section of an annular segment of  FIG. 6A ; 
         FIG. 7  is a magnified perspective view of part of the mandrel of the tool of  FIG. 1  A showing two of the three anti-release safety pins located in their slots prior to the tool set position; 
         FIGS. 8A and 8B  are respective section and plan views of one of the slots in  FIG. 7 ; 
         FIG. 9  is a perspective view of an anchor slip unit with an anti-fracture device according to the present invention; 
         FIG. 10  is a magnified detail of a ratchet tooth impeding retreat of the packing device in  FIG. 3B ; 
         FIG. 11  is a perspective view showing the geometry of the lower cone without slips and the bottom part of the mandrel that come into play for the release movement of the mandrel, and also showing the anti-resetting mechanism; 
         FIG. 12A  is a cross-section of a typical bidirectional symmetrical anchor slip; 
         FIG. 12B  is a cross-section analogous to  FIG. 12A  of an asymmetrical anchor slip having one set of typical teeth and one set of dummy teeth. 
     
    
    
     In all the figures like reference numbers identify like tool parts. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A packer tool or “packer” having a nominal diameter of, e.g., 5½″ (139 mm) is depicted in  FIG. 1A  (notwithstanding that the invention may encompass other standard tool sizes such as 7″, 9⅝″, etc.). The packer includes a mandrel  11  made of ASTM A519 steel type 4140-Y80 crowned, above, by an upper sub  12  and, below, by a lower sub  13 . The three components  11 ,  12  and  13  are made of SAE 4140 tempered steel and, together, span a tool length of about 1.4 meters. A central bore  14  about 50.8 mm (2″) in diameter axially traverses the mandrel  11 . 
     The upper and lower subs  12 ,  13  are provided with threaded joints for connecting other tubing components above and below prior to the run-in operation. This arrangement allows torque to be transmitted down the length of the tool and, during run-in down a well, allows maneuvering of the entire tubing. 
     About the mandrel  11  and between the subs  12  and  13  the tool further includes, from top to bottom, a hydraulic mechanism  15  depicted in  FIGS. 2A ,  2 B and  2 C for setting the tool, a packing mechanism  16  depicted in  FIGS. 3A ,  3 B and  3 C for isolating well layers and an anchor mechanism  17  depicted in  FIGS. 4A ,  4 B and  4 C for keeping the tool affixed to a point in the well while it dwells therein. 
     The hydraulic tool setting mechanism  15  of  FIG. 2A  comprises a hydraulic piston  18  arranged around the upper part of the mandrel  11  to carry out a downward movement during the set operation. The piston  18  is surrounded by a hydraulic cylinder  19  at the top of which a hanger cap  21  is screwed on to prevent it from descending. The piston  18  functions as an actuator during the set operation, when in moves downwards to the position depicted in  FIG. 2B  to activate the packing and anchor mechanisms  16 - 17  as described further on hereafter. 
     A hydraulic chamber  22  is formed about the top of piston  18  to receive pressurized fluid for activating setting through passages  23  that communicate it with the central bore  14  of the mandrel  11 . The hydraulic chamber  22  is closed in by the upper sub  12 , the mandrel  11 , the hydraulic cylinder  19 , the piston  18  and packer seals  24 . 
     Shear pins  26  screwed into the hydraulic cylinder  19  and penetrating through to a slot or depression  27  formed on the outer surface of the piston  18  convey reliability to the setting operation by preventing the latter from moving downwards in absence of sufficient hydraulic pressure in the chamber  22 . To proceed with the set operation once the tool has been run-in down the well, fluid is injected at a predetermined pressure from the mouth of the well into the mandrel bore  14  such that it enters the radial passages  23  and fills the chamber  22 . The effect of this pressure is to urge the piston  18  downwards to the position depicted in  FIG. 2C  as described further on herein, after shearing the threaded pins  26  which are dimensioned to said predetermined setting fluid pressure. 
     In this embodiment, the threaded pins  26  are made of brass, ¼″ (6·35 mm) in diameter and the setting pressure is predetermined according to the number of threaded pins  26 , e.g., 400 psi (2.8 MPa) per pin  26 . The piston  18  and its threaded pins  26  are protected from damage by the hanger cap  21  during upward maneuvering of the tubing through zones of restricted diameter in the casing. 
     However, I have seen that during run-in the pins  26  may be exposed to shear forces in absence of hydraulic pressure, caused by a calibrating ring  28  on a joining member  29  scraping or striking against the inner casing wall and transmitted up by the hydraulic piston  18  and the hydraulic cylinder  19 . Shearing of the threaded pins  26  brings about the risk of the piston  18  prematurely sliding downwards and accidentally activating the packing and anchor mechanisms  16 - 17 . This risk is avoided by means of an antisetting safety mechanism which prevents any downward movement of the piston  18  on the mandrel  11  in absence of the required setting activation hydraulic pressure. This safety mechanism is embodied by a ring segmented into three parts  31  arranged equi-circumferentially in slots in the piston  18  as depicted in  FIGS. 5A and 6A .  FIGS. 6A and 6B  show the preferred shape and proportions of these annular segments  31 . 
     The annular segments  31  protrude radially inwards from the piston  18  fitting into a circumferential slot  32  formed on the outer wall of the mandrel  11  about 10 mm wide and chamfered edges as do the annular segments  31  too (more clearly visible in  FIG. 6B ) so as to retain the piston  18 . At the same time, the hydraulic cylinder  19  acts as a “roof” that prevents the segments  31  from leaving the slots  32  in the mandrel  11 . As a consequence, the piston  18  may not exert a force necessary to shear the threaded pins  26  to enable tool setting. The only way the segments  31  may leave the slot  32  and free the piston  18  is for the cylinder  19  to rise so that the complementary geometries of the cylinder  19  and the piston  18  create a space  33 , as may be seen in  FIG. 2B , sufficient for the segments  31  to leave the slot  32 , as may be seen in  FIG. 5B , and free the piston  18 . However, the cylinder  19  may only budge by effect of the hydraulic pressure in the chamber  22 , since the safety pins  26  prevent any undue ascent thereof. This segmented ring  31  system facilitates tool travel through zones of the casing where the diameter is restricted, without the tool setting prematurely. 
     The segmented ring  31  has a small circumferential notch  34  on its outer cylindrical surface and which continues around the intervening mandrel surface for a retainer ring  36  that softly maintains the annular segments  31  in place through the piston  18  and in the slot  32  when putting the tool together. It is an open ring  36  of relatively thin wire which easily yields and opens when pushed outwards by the annular segments  31  as soon as the latter are freed by the ascending cylinder  19 . Suitable dimensions for the open ring  36  are about 1.75 mm in wire diameter, about 77.0 mm and about 80.4 mm inside and outside diameters, respectively, of the ring  36  and 5 mm separation between its open ends  37  when relaxed. 
       FIG. 3A  shows the packing mechanism  16  comprising three rubber packer seals  38  made of NBR (Nitrile Butadiene Rubber) elastomer, separated by sliding spacer rings  39  and mounted to a seal-holder collar  41  which is engaged by the piston  18  via the joining member  29 . The joining member  29  has a calibrating ring  28  screwed thereon to adjust the amount of deformation of the packer seals  38  into the annular space between the tool and the casing during the set operation. The section of the packer seals  38  includes a chamfered surface  42  which emerges first in response to pressure applied by the joining member  29 , as  FIG. 3B  illustrates, so that a circumferential lip  43  makes first contact and continues to deform against the inner wall of the casing to form a hermetic seal. Once in the set position, the packer seals  38  remain pressed against the casing wall, blocking passage of fluids from one side to the other of the packing  38  in the axial direction of the well. 
     Three anti-release safety pins  47  are fitted in round holes  46  perforating the seal-holder collar  41 . Each pin  47  is made of SAE4140 tempered steel and is formed with a cylindrical or slightly frustoconical stud  48  about 11.0 mm in diameter and about 4.5 mm length and a head  49  which is also cylindrical but larger both in length and section as  FIG. 7  shows, measuring about 19.5 mm in diameter and about 15.5 mm long, forming a smooth piece which is highly resistant insofar it is dimensioned so that the head-stud  49 - 48  transition is be virtually unyielding to shear forces. The head  49  fits snugly in the round orifice  46  through the packing-holder collar  41  and the stud  48  in a respective longitudinal slot  51  machine-cut in the mandrel  11  as illustrated in  FIGS. 8A and 8B . The slot  51  is about 29 mm long, about 12 mm across and about 4.3 mm high in the illustrated embodiment. 
     Since these pins  47  are smooth, a cylindrical cover  52  is provided to retain them and prevent them from falling out of the orifices  46 . In turn, the cover  52  is held in place by three stud bolts  53  screwed on to an upper superior  56  forming part of the anchor mechanism  17 , which detailed further on hereinafter. 
     In  FIGS. 3A and 7 , the studs  48  of the pins  47  are constrained by the corresponding machine-cut slots  51 , thereby locking the mandrel  11  against rotation in relation to the combined packing-anchor mechanisms  16 - 17  (and, hence, relative to the well). The smooth anti-release pins  47  further prevent relative rotation between the tool ends, that is between the subs  12  and  13 , thereby conveying greater reliability to connection and rotation operations on the upper and lower tubing components during mounting at the mouth of the well and later run-in. 
     When the piston  18  advances downwards to activate tool setting, the axial downwardly displacement of the seal-holder collar  41  moves the studs  48  of the pins  47  out of these slots  51 , as seen in  FIGS. 3B and 8 , such that they now have room to turn on the mandrel  11 . As described further hereafter, the release movement is based on a rotation of the mandrel  11  relative to the combined mechanism  16 - 17 , such that the smooth pins  47  prevent accidental occurrence of the release turning movement if the tool has not been previously set. This means that reliability against accidental release depends no more on a single shear-pin release system such that pressure variations which appear either inside or outside the tubing do not affect proper operation of the anchor slips nor of the packing seals mechanisms  16 - 17  any more. 
       FIG. 4A  shows the mechanism  17  of the packer tool for anchoring the tool, comprising: upper and lower cones  56  and  57 , individually slidable axially downwards to respectively activate tool setting and release, anchor slips  58  equi-circumferentially distributed around the mandrel  11  and slidable on ramps  59  machine-cut in the cones  56  and  57 , and a slips cage  61  with individual windows  62  through which the anchor slips  58  may project. This 5½″ diameter tool set forth herein by way of example has three anchor slips  58  arranged at 120° from one another around the mandrel  11  although larger tools may have four or five anchor slips  58 . Each anchor slip generally has a pair of horizontal and parallel teeth sets  63  with sharp edges  64  that bite into the casing wall in the set position and hold the tool fast. Each set  63  spans an outer cylindrical face measuring 60 mm×46 mm on a slip member  66  (alphabetical suffices A, B . . . are omitted when the reference is general), each pair of members  66  of a given slip  58  being longitudinally spaced from and joined to one another by a bridge  67 , all integrated into a single slip piece made of cemented SAE 8620 steel. 
     The anchor slips  58  are initially retracted inside the cage  61  where they are protected during the run-in. The setting operation involves pushing the anchor slips  58  out of the windows  62  to contact the casing wall. In spite of precautions, the anchor slips  58  may suffer damage anyway from different excessive mechanical or thermal conditions to which the tool is exposed during the run-in and, specially, during the lengthy period it dwells inside a well. 
     Failure of an anchor slip  58  may cause its teeth  64  to lose grip on the casing wall and the broken anchor slip to fall back inwards. The eventual loss of contact of an anchor slip  58  loosens the pressure of the remaining anchor slips on the casing wall, which may eventually lead to ineffectual setting of the tool. 
     To prevent this event, according to a feature of the present invention, a pair of external linkage means  68  separate from the bridge  67  and having different structural and mechanical properties are placed along each side of each anchor slips  58  and its end are connected to slip members  66  as shown in  FIG. 9 . Each link  68  is a steel bar  68  of stainless steel—such as SAE 1020—for greater ductility, having a cross-section of 2 mm 2  and its ends are bent 90° and inserted in holes  69  made in each slip member  66 . The sidewalls of the slips  58  have grooves  71  for housing the linkage bars  68  and keep them in the holes  69  of the anchor slips  58 . In this way, the cemented steel material contributes its typical hardness to anchor slips  58  and the external linkage bars  68  relative ductility less prone to failure from jarring and thermal excursions which may fracture an anchor slip  58 . 
     The bridges  67  of the slips  58  are not thermally treated and hence remain ductile. First, the entire piece  58  is cemented, then only the region of the teeth  63  is induction- or flame-heated and the entire piece  58  is tempered. In this way, the slips  58  are hard in the region of the teeth  63  and ductile in the region of the bridge  67  so that, in spite of the latter being the narrower part of the piece  58 , a fracture is more likely to occur in the region of the slip members  66 . As a result, should a substantial part of an anchor slip  58  fracture, the bars  68  will keep the members  66  linked together preventing the broken part from separating. This provides a two-fold advantage of keeping the slip members  66  together and avoiding a big broken slip part from getting in the way of tool operations such as preventing the tool from setting properly. In addition, the loose insertion of the linkage bar  68  ends in the slips member holes  69  provides some articulation as opposed to the rigidness of the bridge  67  connection. 
     Resuming the description of the setting operation, the pressure inside the hydraulic chamber  22  generates two opposing forces, one upwards and the other downwards. The former acts on the hydraulic cylinder  19 , pushing it upwards, and the downward force on the hydraulic piston  18 , urging it downwards. These opposing forces shear the safety pins  26  and enable the hanger cap  21  and the hydraulic cylinder  19  to lift. The annular segments  31  are thereby free to leave the slot  32  in the mandrel  11 , unrestraining the piston  18 . As the piston  18  starts sliding downwards driven by the pressure in the hydraulic chamber  22 , after the three ring segments  31  have been freed as shown in  FIG. 2B , it pushes the rubber seals  38  downwards. Before deforming substantially as shown in  FIG. 3B , the seals  38  transmit this force via a lower calibrating ring  72  to the upper cone  56  which, in turn, forces the slips  58  outwards in a direction perpendicular to the tool axis. This is as a result of the direction of movement being changed from axial to radial by the upper cone  56  wedging under the upper members  66 A of the slips  58  which have an inner surface  73  in the shape of a curved ramp. The radial slip expansion continues until it reaches the inner diameter of the casing with a force that sets the packer tool in the position depicted in  FIG. 4B . A wedge-shape  74  formed on the lower slip member  66 B is concurrently forced up a cylindrical ramp  76  on the lower cone  57  and also assists in pushing the slips  58  outwards. The lower cone  57  is provided with three stops  77  spaced equi-circumferentially on its bottom edge which abut against three snugs  78  formed on the surface of the mandrel  11 . In the preferred embodiment, the cone ramps  73  y  76  and the slip  66  wedges have inclinations of approximately 20° relative to the axial direction and the snugs  78  define an imaginary outer diameter of 82.5 mm. Once the slips  58  are set, the upper cone  56  may descend no more such that the entire axial force from the still down-moving piston  18  now compresses the seals  38 , expanding their diameters and causing them to seal against the casing. 
     As the piston  18  moves down it also drives an open ring  79  downwards. The open ring  79  is provided with sawtooth-like inside teeth  81  which mesh with matching ratchet teeth  82  carved on the mandrel  11  in the path of the ring  79 . The meshing teeth  81 - 82  which define a ratchet are formed by reverse-tap screws having  16  threads per inch (pitch=1.588 mm) on the ring segment  79  and the mandrel  11 .  FIG. 10  illustrates the geometry and dimensions in millimeters of the anti-retreat teeth  81  formed on the ring segment  79 . This ratchet prevents the piston  18  from retreating back up and enables the tool to remain properly set and sealed once the hydraulic chamber  22  has depressurized, hydraulically isolating the upper and lower parts of the tool.  FIG. 2C  indicates the end positions of the lowered piston  18  and of the raised hydraulic cylinder  19  after the fluid has evacuated the chamber  22 . 
     As with the upper calibrating ring  28 , the dimensions of the lower calibrating ring  72  can be adapted to individual well conditions. 
     Accordingly, in this preferred embodiment, the setting mechanism—the first fundamental operation in a useful cycle of a tool of this type—essentially comprises the hydraulic chamber  22 , the hydraulic cylinder  19 , the piston  18 , the joining member  29  with its calibrating ring  28 , the three rubber packer seals arranged about the seal-holder collar  41  of the packing mechanism  16 , the cylindrical cover  52 , the upper cone  56  and the three anchor slips  58 . 
     The second fundamental operation in the tool cycle is release, which consists in moving the lower cone  57  retained by the snugs  78  downwards to allow retraction of the anchor slips  58  and the rubber packer seals  38 . Tool release begins by effectively rotating the tubing 60° to the right. The necessary torque for the mandrel  11  to rotate is given by the number of shear pins  83  screwed into the lower sub  13  which holds the mandrel  11  fast to the lower cone  57  and the lower sub  13 . 
     The release torque applied to the mandrel  11  from above the well first shears the safety pins  83  dimensioned to break when subject to the release torque, thereby enabling the mandrel  11  to turn inside the lower cone  57  thereby displacing the mandrel snugs  78  from their position against the stops  77  of the lower cone  57 , as may also be seen clearly in  FIG. 11 , to a position where the stops  77  face spaces  84  formed between the mandrel snugs  78 , enabling the lower cone  57  to drop about 130 mm (5″) together with the lower sub  13 , sliding along the mandrel  11  to thereby trigger quick release of the tool. The guide snugs  78  of the jay  86 , which come out from their locking position during setting and are guided down the slots  84  cut out in the lower cone  57  to their release position, do so without torsionally uncoupling the mandrel  11  from the lower sub  13 , thereby maintaining release control over the tool torque throughout the tool. 
     During the downward displacement of the lower sub  13 , a notch  87  is uncovered in the jay  86  of the lower cone  57 , allowing pressures to equalize inside the tool and in the annular spacing. This situation enables forced circulation of clean fluid between the tubing and the annular, and towards the surface to wash the length of the tool. 
     The lower cone  57  has a step  88  which, as the cone  57  slides down the mandrel  11 , strikes a complementary step  89  formed in its path on the slips cage  61 , dragging it down together with the anchor slips  58 . As the lower cone  57  descends, the anchor slips  58  loose their foothold on the lower cone  57  and slide along the ramp  76  thereof allowing the anchor slips  58  to retract again against the mandrel  11 . The packer thus becomes unset from the casing. The upper cone  56  also descends a short distance, enough to decompress the rubber packer seals  38 , such that the radial length increases again at the expense of a diminishing diameter and become unsealed. The tool is thus fully released regarding both the anchor and packing mechanisms  16 - 17 . 
     Since pressure conditions down the borehole as well as mechanical friction during tool extraction could push the lower cone  57  back upwards after release, spontaneously resetting the tool sufficiently to impede extraction or otherwise make it more difficult, a restrainer is provided against eventual retreat of the release mechanism. The release mechanism essentially comprises the lower cone  57  and associated means that control and participate in the downward movement just described hereinbefore. This restrainer prevents the lower cone  57  from sliding upwards back along the mandrel  11  thereby avoiding another setting post tool release. The anti-post-release-resetting restrainer comprises an expansible ring  91  around the mandrel  11  housed inside a small triangular recess in the inner surface of the lower cone  57  to define a transversal step  93 . When the cone  57  slides downwards, it drags the restrainer ring  91  down with it until the latter lodges in a circumferential notch  94  formed on the wall of the mandrel  11 , as  FIG. 4C  illustrates, transforming the ring  91  into a safety lock which prevents the lower cone  57  from being able to move back up again under any circumstance once the ring  91  penetrates the notch  94 . Hence, the tool may be reliably handled once released. 
     In this preferred embodiment, the restrainer ring  91  is about 4 mm thick and about 8 mm wide whereas the depth of the notch  94  reduces this part of the diameter of the mandrel  11  down to about 67 mm (2.6″). This measurement is a trade-off between the need of sufficient notch depth to catch the ring  91  without unduly weakening the wall thickness of the mandrel  11 . 
     As in the setting maneuver, the complementary steps  88 - 89  become axially apart as illustrated by  FIG. 4B  and meet again as the lower cone  57  comes down in a manner which sometimes may be hard enough to fracture the anchor slips  58 . As mentioned hereinbefore, broken slips bits are a risk factor which may interfere with the release process. According to an aspect of the present invention, a buffer or damper means formed by a rubber ring  96  is located between the pair of steps  88 - 89 . Preferably, the ring  96  is made of acryl-nitrile D-90 and has a square or rectangular cross-section of about 6.7 mm wide and about 94.3 mm and about 105 mm inner and outer diameters, respectively. 
     Describing the anchor slips  58  in greater detail,  FIG. 10A  exhibits a typical, bidirectional anchor slip  58  having gripping teeth  64  shaped in a triangular cross-section slanted towards a preferred orientation, i.e. like a saw-tooth, in order to oppose substantial frictional resistance against a prevailing axial direction against the casing of the well, compared to the opposite direction. In each typical anchor slip  58 , the preferred slant direction of the teeth  64  of one set  63  is opposite to the other so as to maximize the tool setting power against the casing wall by virtue of both sets of oppositely slanted teeth  63  forming part of the same rigid piece  58 . In the embodiment illustrated in  FIGS. 4A ,  4 B and  4 C, the upper teeth  63  are set against descent and the lower teeth  63  against ascent. 
     One (and most preferably not more than one) of the anchor slips  58 ′ comprises unidirectional teeth  64  in one set and “dummy teeth”  97  as the other. The latter are characterized by blunt rather than sharp edges  64 , for instance by termination in rounded edges  98  when compared to the sharp teeth  64  of the rest of the anchor slips  58 . In addition, the “dummy teeth”  97  furthermore lack a preferred orientation of the teeth  97 , rather they are symmetrical, i.e. not slanted, as  FIG. 12B  shows, in contradistinction to the typical teeth  64  with a preferred orientation shown un  FIG. 12A . I estimate that the radius of the cylindrical curvature of the rounded edges  98  should not be less than about 0.4 mm, preferably not less than about 0.8 mm, to meet the object of the invention. In other words, the set of dummy teeth  97  opposes scant resistance in either axial direction against sliding along the casing wall. 
     This overcomes the potential problem of the teeth  64  “merging” or “integrating” with the casing after a long period of being together in the same biting position. What happens is that, as an anchor release operation begins, the typical set of teeth  64  which partner the set of dummy the teeth  98  becomes unstuck freely and separates from the casing promoting immediate collapse of the typical-dummy pair  58 ′ such that this slip releases first. The loss of a bearing point of the packer tool provides a degree of freedom for transversal movement of the tool to release the two remaining anchor slips  58  with no difficulty. 
     On the other hand, the “dummy” teeth  98  carry out a secondary function by applying a radial force on the casing wall which balances out the radial forces exerted by the “typical” teeth  64  angled at 20°. 
     These features convert the packer of the present invention into an efficient and reliable tool during run-in, setting and release, applicable to well completions requiring lowering, affixing and recovering multiple packers in a single voyage of the tubing, such as in water injection and in hydrocarbon production installations. The mandrel  11  in combination with the lower sub  13  may function as a telescopic joint assuring that movements applied to a particular tool which is being operated are not transmitted to tools located therebelow. 
     A particular embodiment of the invention has been disclosed herein, however changes in materials, shapes, sizes, geometry and arrangement of tool components may be carried out without departing from the purview of the present invention as set forth in claims that follow. For instance, a packer tool having a nominal diameter of 7″ or 9⅝″ may comprise more than three slips.