Downhole Tool to Be Used in a Well Beyond a Restriction

Abstract

The invention is a retrievable downhole oil tool which can travel beyond and set beneath a restriction in casing which has a larger inner diameter than that of the restriction. The tool can later unset and travel back up past the restriction to be retrieved. Design of the tool allows for a larger inner diameter than existing tools with the same outer diameter; slips which reach out further than those of existing tools, from the outer diameter of the tool to the inner diameter of the casing; and several features which prevent damage to the tool while it squeezes through a restriction.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to downhole oil tools which are used during completion and production of an oil or gas well, particularly a retrievable tool which can set securely below a restriction or tight spot in the casing of the well.

Description of the Related Art

When drilling a well, casing is often installed to protect the integrity of the hole. The widest casing is set at the top of the hole, and successively narrower casing must travel down the hole through the wider casings, so that the inner diameter of the well gets narrower as the depth increases. In other words, the inner diameter is wider at the top of the hole, and narrower at the bottom of the hole, and the inner diameter steadily decreases from top to bottom. Occasionally, the casing is installed in a different configuration, with wider casing placed below narrower casing. We call this inverted casing.

Sizes of casing are referred to by outer diameter in inches, and weight in pounds per foot, which can be used to figure the inner diameter. Sometimes a restriction or “tight spot” (these terms used as synonyms in this specification) exists in the casing, which can be caused for example by a casing patch, or inverted casing installation. At the tight spot, the inner diameter of the casing is smaller than the inner diameter below the tight spot or restriction.

An anchor is a tool which is attached to the tubing string, and which may be securely set at a given depth, to keep the tubing and other tools attached to the tubing in vertical place. Each anchor is manufactured to use a given setting method, such as mechanical or hydraulic. An anchor travels down through the hole in an unset state, and then is set using its given method. A mechanical anchor, like the one described herein, can be set and released and re-used many times; although it sets securely at a given depth, it is not permanently set there. Mechanical anchors are cost-effective and versatile, in that the operator can release the anchor and re-set it at any time.

One type of anchor is a tubing anchor catcher, which is used during production to anchor the tubing string at a desired depth, and also to catch and prevent any parted tubing pipe from falling into the well. As with all downhole oil tools, the operator normally chooses a tubing anchor catcher with the largest outer diameter and largest inner diameter possible, dependent upon the inner diameter of the casing which is present at the depth where the anchor is intended to set. A tool with a large inner diameter is desirable so that the greater volume of fluid or gas per time period can travel down or up through the inside of the anchor.

The mechanical rotational setting mechanism of an anchor must be quite precise in order to work properly. When the anchor reaches the appropriate depth, the operator rotates the tubing, which begins the process of engaging the setting mechanism. The drag springs or blocks must touch the casing with sufficient friction and force so as to prevent the slip cage from rotating. The drag spring cage must also stay in the same precise vertical relationship with the slip cage, with the exact distance between them preserved, so that when the cone moves downward, the slips are in the right place, allowing the cones to push out the slips evenly and correctly, and causing the slips to get a secure hold on the casing with even amounts of pressure along the entire surface area of the several slips.

Several problems exist when attempting to lower and set a retrievable anchor below a tight spot: 1) The drag springs or blocks must be able to contact the casing with sufficient force at the wider setting depth, but also pass through the narrower tight spot without deforming permanently. 2) The drag spring assembly must make a tight squeeze through the restriction without moving vertically up or down in relation to the rest of the tool. 3) While the outer diameter of the entire tool must be small enough to pass through the tight spot, it is still desirable to have the biggest inner diameter possible inside the tool. 4) Depending upon their placement in the tool, the shear pins or screws may be very difficult to access and change; or they may be exposed to fluids, debris and corrosion in the well, causing them to clog and may be impossible to change out; or a tight spot may cause them to be prematurely sheared. 5) The slips must somehow extend further out than usual in order to set securely against the wider casing. 6) The slips must set with sufficient outward force to hold securely, without deforming the casing. 7) Finally, the tool must be able to release, retract slips and pass through the restriction when coming out of the well.

Tight spots happen occasionally, and the inventors are unaware of any retrievable mechanical or hydraulic anchors which can successfully travel through a tight spot and set in casing below with a wider inner diameter. Sometimes the operator must resort to setting a tubing anchor catcher with a smaller outer diameter directly in the tight spot or casing patch, thereby settling for a smaller inner diameter in the tool, causing slower production. Sometimes an operator will abandon a well because it is too expensive to solve all of the problems associated with a tight spot.

BRIEF SUMMARY OF THE INVENTION

This invention is a downhole oil tool which successfully travels through casing restrictions; sets securely in wider casing below; has a large inner diameter; and, if mechanically set, retains all benefits of a mechanically set tool including affordability, a high pressure rating, removability, reusability, and no need for special equipment. The tool can achieve this through a combination of several separate improvements and innovations in its design:

• • A backup ring which contacts the mandrel along the entire inner surface area of the backup ring, as well as along a portion of the top and bottom surface area of the backup ring, so as to robustly prevent the drag spring assembly from moving vertically closer to or further from the cone below;
  • Shear pins which are easily accessible and not trapped inside the slip cage or drag spring cage, and are also protected by a shear pin cap;
  • The spatial relationship of the drag spring assembly and the slip assembly: they are not radially concentric, but instead the entire drag spring assembly is positioned completely above or below the slip assembly, helping make the outer diameter of the entire tool smaller while keeping the inner diameter as big as possible;
  • Use of drag springs rather than conventional drag blocks, because drag springs are able to compress through a tight spot, and conventional drag blocks cannot compress or extend far enough;
  • A drag spring cage with a narrower outer diameter than the slip cage, to combat the problem of drag springs permanently deforming if they compress too much and scrape too hard against a narrow casing or restriction;
  • Use of conical springs or leaf springs to push the slips inwards while in running (unset) position; both conical springs and leaf springs compress farther than regular coil springs, allowing the cone to push the slips out farther than a cylindrical coil spring would allow;
  • A stationary lower cone which is longer than the moving upper cone, so that as the upper cone travels down the mandrel toward and underneath the slips, it has more time and area to push the slips out a greater distance than a conventional anchor slip assembly would;
  • Slips designed with a groove vertically down the middle, to accommodate the conical springs in the resulting pocket, and making each slip have two long and thin surface areas to contact the casing. The slip may also include a leaf spring in its pocket instead of conical springs. More points of contact supporting the same load makes deformation of the casing less likely; and
  • Extra long slips which are pushed out and supported by extra long cones, to enhance the robustness and security of the contact with the well casing while in set position.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a full exterior view of an anchor with the setting mechanism of slips in running (unset) position, before it is set in the casing.

FIG. 2 shows a lengthwise cutaway view of the anchor in FIG. 1.

FIG. 3 shows a full exterior view of the same anchor shown in FIGS. 1 and 2, which has been set in the well casing with the well casing shown cut away. The setting mechanism is shown holding onto the casing.

FIG. 4 shows a lengthwise cutaway view of the anchor shown installed in casing in FIG. 3.

FIG. 5 shows a transverse cutaway view of the same anchor shown in FIGS. 1 and 2, in its running (unset) position with slips fully retracted, cut at the level of the upper slip spring, and viewed looking up.

FIG. 6 shows a transverse cutaway view of the same anchor, cut at the same level as FIG. 5, except that the slip mechanism is shown in its set position, with slips fully extended, and viewed looking up.

FIG. 7 shows a partial lengthwise cutaway view of the same anchor shown in all previous figures, and shows the slip assembly portion of the tool in its running (unset) position, with slips fully retracted.

FIG. 8 shows a partial lengthwise cutaway view of the same anchor shown in all previous figures, and shows the slip assembly portion of the tool in its set position, with slips fully extended.

FIG. 9 shows an embodiment of the slip used in the anchor previously pictured.

FIG. 10 shows an enlarged cutaway view of a portion of the anchor in FIG. 1, including the backup ring and stop ring.

DETAILED DESCRIPTION OF THE INVENTION

The subject of this invention is a retrievable downhole oil tool which can pass through a restriction of small inner diameter in the casing, and then set in a lower larger inner diameter of casing. Design of the invention allows the tool to have an outer diameter small enough to pass through the tight spot or restriction; an inner diameter which is as big as possible; and a setting mechanism which is able to expand sufficiently to securely set in the lower wider casing. Features of the invention also allow the tool to retain functionality without damage after squeezing through a restriction.

This paragraph contains a very high level description of how a downhole oil tool such as this works. The tool is basically a hollow tube with parts mounted on the outside circumference. The parts on the outside are precisely mounted on the tube and in relation to each other, to make it possible for the tool to set securely in one spot down in the well for a period of time, and also for the tool to be unset and retrieved later. In a mechanically set tool, in order to set the tool, the operator rotates and lifts the tube, and a large group of the mounted parts stays vertically stationary and does not rotate or move up with the tube. A small group of parts does rotate and move with the tube, and that group of parts interacts with the stationary group of parts, ultimately causing some of the vertically stationary parts to move radially outwards and push against the inner wall of the well with sufficient force to keep the tool anchored at that spot. When it is time to retrieve the tool, the operator rotates the tube in the opposite direction, reversing the setting process, and causing the rotating group of parts to move back into original position, which causes the anchoring parts to move away from the inner wall of the well, releasing the tool. Sometimes the tube can no longer rotate, due to debris or corrosion inside the tool; in this case, an emergency backup method is used, lifting the tube straight up with a greater amount of force sufficient to shear some small pins or screws, allowing some of the parts to loosen so that the anchoring parts are no longer forced out against the inner wall of the well. Either way, the tool can then be retrieved.

FIGS. 1 and 2 show an embodiment of the invention in its running (unset) position, with slips 13 retracted to minimize the outer diameter of the tool as it travels up or down inside the hole. FIGS. 3 and 4 show the same embodiment of the invention in its set position, installed inside the casing. This tool is installed in casing in the orientation shown, with 1 on the top and 20 on the bottom.

1 is a top sub, which is screwed onto the outside of the mandrel or body 2. The top sub is also threadedly connected with the tubing 22, as shown in FIGS. 3 and 4. The hollow mandrel 2 extends from the top to the bottom of the tool, and all of the other parts are mounted upon the mandrel 2 in various ways. The mandrel 2 has a stop ring 3 and a backup ring 4 installed below the top sub 1, in a groove which has been cut into the mandrel 2, with a precise amount of space left between the top sub 1 and the top of the stop ring 3. See FIG. 10 for a detailed view of the backup ring 4 area of the tool. The backup ring 4 securely fits into the groove on the mandrel 2 such that the backup ring 4 does not move up along the axis of the mandrel 2, and the backup ring 4 may or may not rotate with the mandrel. The backup ring 4 is actually a ring divided into two pieces along the line of its diameter, which permits it to be installed in the groove of the mandrel 2.

The stop ring 3 is threadedly attached to the top of the drag spring cage 6, and these two parts closely surround the backup ring 4, preventing the two pieces of the backup ring 4 from separating or coming loose. The stop ring 3 is loosely attached to the mandrel 2 so that when the mandrel 2 rotates during the setting procedure, the stop ring 3 will not rotate. A set screw 5 keeps the stop ring 3 and drag spring cage 6 together, so that the connection between the two does not come loose. The drag spring cage 6 is located both radially outside and below the backup ring 4, and contacts the outside and bottom surfaces of the backup ring 4 which is sticking out of the groove. The drag spring assembly is made up of a drag spring cage or housing 6, which surrounds but is not fastened to the mandrel 2; and the drag springs 7 which are securely attached to the outside of the drag spring cage 6 with drag spring screws 8.

The slip assembly is located directly below the drag spring assembly, and it is securely fastened to the drag spring assembly with a set screw 10. FIGS. 1 and 3 show the location of said set screw 10, although the set screw would not be visible in these views. Said set screw 10 keeps the drag spring cage 6 and slip cage 9 together, so that the connection does not come loose. The slip assembly also surrounds but is not fastened to the mandrel 2. FIGS. 5, 6, 7 and 8 show the slip assembly in greater detail. The slip assembly consists of a slip cage 9 with cutouts; the slips 13 which extend out through the cutouts during the setting procedure; and conical springs 14. Each slip 13 has a slot or pocket, shown in FIGS. 5, 6 and 9, which is where conical springs 14 rest, touching the underside of the slip cage 9. Leaf springs may also be used instead of conical springs. FIGS. 3 and 4 show the location of the conical springs 14, although the conical springs 14 would not be visible in these views. When extended, the toothed surfaces of each slip 13 project through cutouts in the slip cage 9, and each slip 13 straddles a portion of the slip cage 9.

An upper cone 12 is threadedly connected with the mandrel 2, and is situated between the mandrel 2 and the upper end of the slip cage 9. Pipe plugs 11 are attached to the upper cone 12, and the pipe plugs protrude outward through cutouts in the slip cage 9. These cutouts (see pipe plugs 11 in FIGS. 1, 2 and 3) are separate from the cutouts located at the slips (see slips 13 in FIGS. 1, 2 and 3.) The pipe plugs 11 prevent the upper cone 12 from rotating with the mandrel 2 during the setting and unsetting procedures. A lower cone 15 is installed surrounding the mandrel 2 between the mandrel 2 and the slip cage 9, within the lower end of, but not affixed to, the slip cage 9. Radially inside the lower portion of the lower cone 15, the bottom sub 16 is threadedly connected to the mandrel 2, and a set screw 16 prevents the bottom sub 20 and mandrel 2 from unscrewing and separating. An O ring 17 is installed just under the set screw 16, between the bottom sub 20 and the mandrel 2, to provide a seal at that connection. Said O ring 17 is shown in FIGS. 2 and 4, and its location is shown on FIG. 3, although the O ring 17 would not be visible in this view.

Shear pins 19 covered by a shear pin cap 18 are situated below the slip assembly. Each shear pin 19 is embedded in the bottom sub 16 and protrudes radially outward, such that it holds the lower cone 15 in place and prevents it from sliding axially downward. As shown in FIGS. 2 and 4, the upper portion of the lower cone 15 has a smaller inner diameter, where it contacts and surrounds the mandrel 2. The lower portion of the lower cone 15 has a larger inner diameter, to accommodate the bottom sub 16 which has a larger outer diameter than the mandrel 2. The difference between the inner diameters of the lower cone 15 creates a shoulder which will be significant during an emergency backup unsetting procedure. In the event that the normal manual unsetting procedure fails, then the emergency backup unsetting method involves pulling up on the tubing 22 and mandrel 2 with sufficient force to shear off the shear pins 19. The lower cone 15, no longer supported by the shear pins 9, falls downward until its shoulder rests on the top of the bottom sub 16.

The outer diameter of a tool including the innovations of this invention is reduced, as compared to typical tools of a given inner diameter, by moving the drag spring assembly to a position above or below the slip assembly, rather than at the same level. FIGS. 1, 2, 3 and 4 show the drag spring assembly installed above the slip assembly. Most anchors have these two assemblies at the same level, with the drag springs or blocks radially outside of the slips. The conventional design allows the tool to be axially shorter, which is desirable to avoid the tool getting stuck if must pass through a dogleg in the casing. However, when comparing a conventionally designed tool of a given inner diameter with the innovative tool of this invention with the same inner diameter, the conventional tool would have a larger outer diameter.

A tool which includes the innovations of this invention must use drag springs rather than conventional drag blocks, because drag springs can compress without deforming when passing through a restriction. In addition, the drag spring cage 6 has a smaller outer diameter than the slip cage 9, which minimizes the compression of the drag springs 7, further reducing the risk of permanently deforming the drag springs 7 when squeezing through a restriction.

Two additional features prevent damage to the tool while it passes through a restriction: first, the backup ring 3 located below the top sub 1 and above the drag spring cage 6 contacts the mandrel 2 in a groove with the backup ring's full inner surface area, as well as with a portion of the backup ring's top surface area, rather than being attached to the mandrel 2 with a conventional body nut. This contact area makes the backup ring 3 exceptionally robust, so that it will not fail when the tool passes through a tight spot, when the drag springs 7 will squeeze against the casing 21 and cause the drag spring housing 6 to push up hard against the backup ring 3. The purpose of the backup ring 3 is to keep the various parts of the tool which surround the mandrel 2 exactly in place and in the correct vertical placement in relation to each other, so that the setting mechanism will work properly. FIG. 10 shows an enlarged view of the backup ring and surrounding parts.

The second additional feature which prevents damage to the tool while passing through a restriction is a shear pin cap 18, which protects the shear pins 19 at the bottom of the tool while allowing them to be easily accessible. The purpose of the shear pins 19 is to be able to release the tool as an emergency backup method, so that it can be retrieved. Depending upon conditions of the well where the tool will be set, the operator may want to change the shear pins 19 before attaching the tool to the tubing string 22. The placement of the shear pins 19 under a shear pin cap 18, rather than the conventional placement of shear pins between the housing and the cone, makes it much easier to change out the shear pins 19. The shear pin cap 18 is easily removed by the operator with a wrench. Shear pins are usually placed deep within the tool so as to shorten the tool, but this makes changing the pins a tedious job, requiring the operator to substantially take apart the tool to access the shear pins.

Some tools use shear screws, which are supposed to be easier to replace because they are easily accessible on the outside of the tool, but in practice, the heads of the screws often get covered with debris and corrode while the tool is in the hole, and the screws are then impossible to remove. The shear pin cap 18 protects the shear pins 19 from debris and corrosion in the hole, as well as from being prematurely stressed and/or sheared against the casing 21 while passing through a tight spot.

After the tool passes through a tight spot, it must then extend out and set securely in casing 21 which has a larger inner diameter than the restriction. The tool is able to do this because of the innovative slip assembly design, which is shown in FIGS. 5, 6, 7 and 8. Each of the slips 13 is axially longer than normal, and has a slot, or pocket, partially machined out of the outer toothed side, from top to bottom, so that the toothed outer surface of each slip 13 is divided into two separate toothed surfaces, still connected on the undersurface. See FIG. 9 which shows a slip by itself. FIG. 7 shows a slip on the right which is cut away in the middle, so that its base is cut away and shaded, and the outer portion of the slip is not cut away, because of the existing slot, so it is not shaded. Each slip 13 is contained within the slip cage 9, with conical springs 14 which fit exactly in the pocket, and which contact both the underside of the slip cage 9 and the outer surface of the pocket in the slip 13. In running (unset) position, these springs 14 are uncompressed and push the slips 13 inside of the slip cage 9, so that the outer edges of the slips 13 do not extend outside of the slip cage 9 at all. FIGS. 5 and 7 show different views of the slip assembly design in running (unset) position, with slips 13 fully retracted. FIG. 5 shows the tool cut at a point at the bottom edge of the upper conical spring 14—see FIG. 2. The slips 13 are touching the mandrel 2, and the upper cone 12 is shown above the slips 13, not contacting them at all yet.

During the setting process, the operator rotates the tubing 22, which causes the mandrel 2 to rotate, but the drag springs 7 prevent the slip assembly from rotating. Pipe plugs 11 are attached to the upper cone 12 to prevent the upper cone 12 from rotating with the mandrel 2. Rotation of the mandrel 2 causes the upper cone 12 to travel downward on a threaded portion of the mandrel 2 toward the slips 13 and the stationary lower cone 15. The angle of each conical surface matches the angle of the underside of each slip 13, and so as the upper cone 12 moves down under each slip 13, it pushes the slip 13 downward, causing the entire slip cage 9 to move downward toward the stationary lower cone 15.

Between the time that the upper cone 12 first contacts the upper edge of the slips 13 and the time that the lower edge of the slips 13 first contact the lower cone 15, the slips 13 do not move radially outward very much, because the conical springs 14 which rest in the pocket of the slips 13 and contact the slip cage 9 provide resistance against outward movement. When the underside of the slips 13 meet the lower cone 15 however, further travel of the upper cone 12 down the threaded portion of the mandrel 2 causes the slips 13 to move radially outward as well as down, as they are pushed outward along the slanted edges of both the upper 12 and lower cones 15. Since the slips 13 can no longer move downward easily, the force of the upper cone's 12 movement overcomes the springs' 14 resistance and the slips 13 are pushed outward until they forcibly grip the well casing 21. The slips 13 themselves and the conical surfaces of both cones are longer than normal, which allows the slips 13 to be pushed out farther at a conventional angle.

As each slip 13 is pushed radially outwards, the conical springs 14 between the slip 13 and the slip cage 9 are compressed. When fully compressed, the conical springs 14 are basically flat, allowing the slips 13 to extend outwards as much as possible, more than conventional cylindrical springs in the pocket would allow. Leaf springs have the same function as conical springs, in that they push the slips inside of the slip cage while the tool is in running (unset) position, and the leaf springs are basically flat when fully compressed, when the tool is set. FIGS. 6 and 8 show the slip assembly in set position, with the cones 15 pushing out the slips 13, and the slips 13 sufficiently extended to reach out to the casing wall 21. The two white donut-shaped areas in FIG. 6 represent the upper cone—the inner part is the lower edge of the cone, closest to the viewer, and the outer part shown is the conical sides of the cone, the outer diameter increasing as it gets further from the viewer. Note that FIG. 6 shows the tool in set position, but not installed in casing—if it were installed in casing, the drag springs would be compressed by the casing, and would radially reach out the same distance as the slips. Using springs which compress so much is important to the design, because the reduced space between the inner diameter and the outer diameter of the tool limits the possible thickness of the slips. The slips must extend outwards farther than slips in a conventional tool, since the outer diameter of the tool is reduced in order to pass through a restriction, and so it is important that the springs not reduce the extent to which the slips can jut outward and grab onto the wider casing.

The slip design has more points of contact with the casing than conventional tools of this kind, since each slip is effectively made into two separate toothed surfaces. See FIG. 9. Having more points of contact with the casing is desirable to reduce the likelihood of deforming the casing during the setting procedure. Since each slip is effectively cut in half and made narrower than normal, the longer length increases the surface area of the contact points.

While the embodiment of the invention shown in the figures is a mechanically set tubing anchor catcher, other embodiments may be devised without departing from the basic scope of the invention. Such other embodiments would use the features of the invention in a hydraulically set tubing anchor catcher, as well as in a different tool which mechanically or hydraulically sets in a well, such as a packer or plug. The inventors also envision that the invention may be used in a well without a restriction, since the tool has a larger inner diameter than is usually possible in a tool with a given outer diameter.

Claims

1. A retrievable downhole oil tool intended to set in a well, comprising:

(a) A slip cage and a drag spring cage that are not radially concentric with each other; and

(b) A drag spring cage which has a smaller outer diameter (not including any drag springs or blocks) than the slip cage; and

(c) A plurality of slips which each have a vertical slot in the middle; and

(d) Conical or leaf springs trapped between the slot of each slip and the underside of the slip cage.

2. The tool of claim 1, which additionally comprises a backup ring surrounding a mandrel; which backup ring has contact with the mandrel along the backup ring's entire inner surface; and which backup ring prevents the drag spring cage from moving up along the mandrel.

3. The tool of claim 1, which additionally comprises:

(a) Shear pins located above or below the slip cage and drag spring cage; and

(b) A shear pin cap which protects the shear pins.

4. The tool of claim 2, which is set by a mechanical method.

5. The tool of claim 3, which is set by a mechanical method.

6. The tool of claim 1, which additionally comprises

(a) An upper cone which moves down along a threaded portion of the mandrel; and

(b) A lower cone which does not move in relation to the mandrel, and which is longer than the upper cone.

7. The tool of claim 1, which is a tubing anchor catcher.

8. The tool of claim 2, which is a tubing anchor catcher.

9. The tool of claim 3, which is a tubing anchor catcher.

10. The tool of claim 4, which is a tubing anchor catcher.

11. The tool of claim 5, which is a tubing anchor catcher.

12. The tool of claim 6, which is a tubing anchor catcher.

13. A method of making a downhole oil tool which can travel beyond a restriction in a well with casing, which can securely set in a location beyond the restriction where the casing has a larger inner diameter than that present at the restriction, and which can later be retrieved and successfully travel past the restriction, comprising the steps of:

(a) Choosing a mandrel with a smaller inner diameter and a smaller outer diameter than the inner diameter of the casing at the restriction;

(b) Mounting a generally tubular drag spring cage and a generally tubular slip cage on said mandrel in positions surrounding the mandrel such that the two cages are not radially concentric;

(c) Choosing a drag spring cage with a smaller outer diameter than that of the slip cage;

(d) Choosing slips with a toothed side and a smooth side opposite to the toothed side, which slips each have a slot positioned vertically on the toothed side, such that the toothed side of the slip is divided into two surfaces, while the smooth side is left intact;

(e) Choosing conical springs or leaf springs; and

(f) Installing a plurality of said slips radially in between said mandrel and said slip cage, and inserting one or more conical springs or leaf springs into the slot of each slip, such that each spring is trapped between the slot of a slip and the slip cage.

14. The method of claim 13, additionally comprising the step of:

(g) Installing a backup ring on a groove on said mandrel, which backup ring has contact with the mandrel along the backup ring's entire inner surface; and which backup ring prevents the drag spring cage from moving up along the mandrel.

15. The method of claim 14, additionally comprising the steps of:

(h) Installing a plurality of shear pins in a location on the tool which is axially below both the drag spring cage and the slip cage; and

(i) Installing a shear pin cap concentrically outside of the shear pins, thus protecting said shear pins from substances and forces in the well.