The following 5 Packer setting mechanisms are discussed in this article:

1. Compression set anchor packer
2. Mechanically set compression packers
3. Mechanically set tension packer
4. Hydraulic set tension/compression packer
5. Action of hydraulic hold-down

1. Compression set anchor packer

The anchor packer is the simplest of the compression packers. In the running-in position, a collet latch is in a receptacle and the rubber sealing element is retracted allowing it to pass freely down the well.

When the Tail-pipe, run below the packer, encounters the bottom of the well, the weight of the tubing above the packer causes the collet to snap out of the receptacle. The tubing weight compresses the sealing element between the top and the bottom subs causing it to extrude and pack-off against the casing.

If the packer is to be set some distance off bottom, the long tailpipe, required to initiate and maintain the pack-off, is inexpedient. It is cumbersome, it may buckle badly and, in time, may become sanded in.

2. Mechanically set compression packers

2.1 Application

These packers can be used in drill strings or tubing strings where the pressure differential is expected to be from above the packer. A mechanically set compression packer is regularly used for drill stem tests or to locate casing leaks. When this Packer is used for drill stem testing purposes care must be taken to ensure that the pressure below the packer does not exceed that from above. However, should this occur the packer will remain seated as long as the resulting upward force is less than the compressive force of the slacked-off tubing weight.

2.2 Operation

The number of slips on this type of packer varies depending on its size. They are evenly spaced around the slip retainer ring. A stud, projecting through the slip ring, locates in a J-shaped slot, machined in the outer surface of the packer body. When the stud is located in the short leg of the J-slot, the slip ring and the slips cannot move up towards the cone. In this mode the packer cannot set. When running into the well, springs cause the lower part of the slips (the wear pads) to bear against the casing wall. The slip retainer ring acts as a fulcrum and the upper toothed part of the slips pivot inwards away from the casing wall. The friction of the wear pads on the wall holds the stud firmly up in the short leg of the J-slot. This ensures that the slips are retained in a down position clear of the cone.

2.3 Setting the packer

On reaching the desired setting depth the tubing is picked up a few inches. The stud will now be located in the lower end of the short leg of the J-slot. Rotation of the tubing at surface in the prescribed direction and amount of turns brings the J-slot round until the stud lies in the lower end of the long leg. The tubing is now lowered and the packer body moves down relative to the slip ring (the length of the long leg of the J). The expander mandrel moves behind the slips which forces them out against the casing wall. This mechanically set, retrievable compression packer is supported in the well by the slips. The Packing element is expanded, and compressed between the body and the cone by slackening-off the tubing weight. This effects a seal between the tubing and casing.

2.4 Retrieving the packer

Prior to retrieval any differential across the packer must be equalised. This packer can now be retrieved simply by picking up the tubing/drill string weight, plus a slight overpull to unseat the packer. The slight overpull combined with the upward movement of the tubing/drill string allows the compression between the body and cone to relax. In turn the packing element contracts to its original form and the expander mandrel moves up from behind the slips allowing them to retract into the slip carrier. The packer can now either be retrieved from the well or reset further up the hole.

2.5 Operation of J-slot

The J-slot principle, as a means of controlling the slips, is used on many mechanically set packers. It is simple and, providing the manufacturer's operating instructions are followed, fool-proof. A variant of the packer described above has the stud fixed in the packer body and the slot cut in the inner surface of the slip ring. The slot is then in the form of an inverted letter J. Other mechanically set packers use a screw thread, instead of the J-slot, as a means of controlling the slip ring. Several turns at surface are required to set these packers.

• Some mechanically set packers set with right hand rotation, and some with left. This must be checked with the manufactures' operating instructions. In either case the operator who runs the packer should check the necessary rotation, physically, before starting the packer in the well, at the same time ensuring that the slip ring is able to move to the set position.
• The weight to be slackened off to effect the seal depends on the hardness off the rubber, and will vary with the size of the packer. The manufacturer's operating instructions must be consulted.
• On some mechanically set packers, using the stud and slot principle, the slot is cut such that, on lifting the tubing to release the packer, the stud automatically 're-jays' back into its running-in position.

3. Mechanically set tension packer

3.1 Application

This packer was designed for use in installations where the pressure differential is expected to come from below. In the mechanically set, retrievable, tension packer, the sealing element is below the slip assembly. When the slips are released from the running-in position, an upward pull on the tubing brings the cone up under the slips forcing them out to grip the casing. Further upward pull compresses the packing element and packs it off against the casing wall. Pressure differential from below will set the packer yet more firmly. If the differential should come from above, the packer will remain seated only as long as the resulting downward force is less than the tension left in the tubing. Thereafter the packer will be forced down, further stretching the tubing.

3.2 Operation

The packer in the illustration has an inverted J-slot machined in the packer body, engaged by a stud on the slip ring. To set the packer, the tubing is lowered a few inches, and rotated anti-clockwise at surface a sufficient amount to give a quarter turn at the packer. The stud is now in the top of the long leg of the J-slot. Pulling up on the tubing sets the packer. The tubing must be landed in tension. To release, the tubing must be lowered at least a foot more than is necessary to remove the originally applied tension, and then rotated clockwise. This last movement brings the short leg of the inverted J-slot under the stud. The packer may be pulled from the well. Tension packers are often equipped with an additional, emergency release device. In the case of the packer illustrated this takes the form of a shear ring. If the normal releasing procedure is not successful, a heavy upward strain on the tubing, considerably heavier than that required to set the packer, will shear the ring, permitting body, rubber and cone to drop down the mandrel, thus freeing the slips.

4. Hydraulic set tension/compression packer

4.1 Application

Hydraulically set packers are particularly suited to conditions where tubing manipulation might be problematic due to well characteristics, e.g. high deviation excessive depth etc. Due to the design of this packer the tubing can be landed and flanged up prior to it being set. This is especially attractive on semi-sub or drill ship locations since any "yo-yoing" effect of the tubing is eliminated.

4.2 Operation

The hydraulically set packer is actuated by a pressure differential between tubing and casing, at the packer. A means of temporarily plugging the tubing must be incorporated in the tubing below the packer, or in the bottom of the packer itself. In Fig. 2391, this is an expendable seat held in place by a shear pin. On reaching setting depth, a ball is dropped down the tubing, to land on the expendable seat. The tubing pressure is built up by a pump at surface. Tubing pressure, working in the cylinder, has forced the body downwards, relative to the mandrel. The rubber sealing element has been compressed to pack off against the casing, and the cone has been forced down behind the slips, driving them outwards to grip the casing. The pressure has also actuated the hydraulic hold-down buttons. A shear pin, or pins, holds the body and the mandrel together in the unset position while running in, to prevent premature setting. The first action of the setting pressure is to shear the pin. With the packer set, a further increase of pressure in the tubing will shear the pin and the ball and seat will fall out of the bottom of the tubing. The setting pressure will now be bled off, but the packer will remain seated as the small internal slips hold the body and the mandrel relative to one another. This packer does not require tubing weight to hold it in position. Pressure differential from below could unset it, but for the hydraulic hold-down. The hydraulic hold-down is not always included, but when it is, the packer becomes a tension-compression packer.

4.3 Retrieval of the packer

The packer is released by raising the tubing. A pull, at the packer, of some 20,000-30,000 lb, depending on size, shears the release pins. The lower body (l) will slide down to the retaining shoulder, followed by the slips and the cone, allowing the rubber sealing element to retract.

4.4 Hydraulic variation

A variant of the hydraulically set packer is the hydrostatic packer. This has an annular cylinder containing air at atmospheric pressure incorporated in its body. The upper end of the cylinder is sealed by an annular piston, temporarily locked in position. A relatively low pump pressure at surface shears a small pin, unlocking the annular piston. Hydrostatic head in the tubing, acting on the top of the piston, moves it down, compressing the air. This movement sets the slips and compresses the sealing element. The movement is locked into the packer by internal slips. Thus in performance and application the hydrostatic is very similar to the hydraulically set packer. The main difference is the lower surface pressure required to set it.

5. Action of hydraulic hold-down

5.1 Application

Hydraulic hold-down buttons are an integral part of hydraulic set packers. They are situated at the upper end of the packer above the packing element. These buttons rely on differential pressure from below the packer to force them out into the casing wall thus, preventing any upward movement of the packer. The higher the differential pressure from below the packer, the harder the hydraulic hold-down buttons will engage the casing wall.

5.2 Operation

The button is retained in its port by a steel strip, the button retainer. A deep vertical slot down the face of the button allows the latter to move outwards. A spring (or springs) in this slot bears against the retainer strip, and forces the button inward. This keeps the button, when it is not needed, out of contact with the casing and preserves the teeth from wear. The spring should be sufficiently strong to prevent pressure surges (temporary differential due to the piston effect) extruding the buttons while running the packer. The pressure differential across the button is contained by an 'O'-ring seal. The condition of the seals should be checked before running, or re-running, the packer. If the seal is ineffective, the button will not set, and, more seriously, a leaking seal is a leaking packer. Pressure from below the packer, transmitted via the passage in the packer body to the back of the button, is equal to, or less than, the pressure from above, acting on the face.