GB2292400A - Downhole packer - Google Patents

Abstract

A downhole packer has gripping means disposed on the exterior of a tubular body 1 which are selectively operable to grip a surrounding casing. The gripping means comprises two sets of slips 11, 34 which are operable by respective pistons 18, 36. The pistons 36 are moved by pressurised fluid tapped from the annulus between the tubular body 1 and casing at a point below packing elements 3, 5. <IMAGE>

Description

"Downhole Packer" This invention relates to a downhole packer for use in oilwells and the like.

It is common practice to include a packer in production tubing run into an oilwell casing for the purpose of closing off the well until a time when production is desired. Packers may be of a semi-permanent nature, requiring to be retrieved by milling or cutting which is difficult or time consuming. Other packers are designed to be more readily removable; however this typically relies on the provision of a shear element such as a shear wire which is sheared by an upward pull on the production tubing, and this has the disadvantage that pressure surges downhole may cause premature rupture of or damage to the shear element.

The present invention provides a downhole packer comprising a tubular body, gripping means disposed on the exterior of the tubular body and selectively operable to expand into gripping engagement with a surrounding casing to fix the tubular body in position in the casing, and sealing means disposed on the exterior of the tubular body and expandable into engagement with the casing to seal the annulus between the tubular body and the casing; and in which the gripping means includes force producing means operated in use by pressurised fluid tapped from said annulus at a point below said sealing means.

In a preferred form of the invention, the gripping means comprises a first set of slips and a second set of slips, the first set of slips being operable by first piston means powered by pressurised fluid from within the tubular body, the first piston means also operating to produce expansion of the sealing means, and the second set of slips being operable by second piston means powered by said fluid pressure tapped from the annulus.

Preferably, the second piston means has a surface area presented to said fluid pressure which is greater than the combined surface area of the exposed sealing means in the annulus and the end surface of the tubular member. This may conveniently be achieved by providing the second piston means in the form of a plurality of (for example, three) axially spaced annular piston elements disposed around the piston body.

The second piston means preferably includes spring means providing an initial bias force countering said fluid pressure. This ensures that the second set of slips is disengaged in the absence of said fluid pressure to enable removal of the packer.

Preferably, said pressurised fluid is communicated from the annulus below the sealing means via one or more axial passageways in the wall thickness of the tubular member. In a particularly preferred form, there are two such axial passageways which are arranged parallel to an access line passageway extending along the tubular body. Conveniently, the tubular body has a main through bore which is eccentric with respect to the exterior surface of the tubular body, thereby providing a thicker wall portion in which said passageways may be accommodated.

An embodiment of the present invention will now be described, by way of example only, with reference the drawings, in which: Figs. la, 1b and lc when assembled together form a side view in half-section of a packer forming an embodiment of the invention; Figs. 2, 3 and 4 are transverse cross-sections taken on the lines W-W, X-X and Y-Y respectively of Fig. 1; and Fig. 5 is a scrap cross-sectional side view of part of the packer of Fig. 1 rotated through an angle of approximately 100.

Referring particularly to Fig. 1, a packer comprises a tubular mandrel 1 with screw-threaded ends 50 and 51 for securement in production tubing (not shown). In use, the packer is run in on the production tubing to the desired location. To set the packer, a blanking plug is run on wireline to a nipple in the production tubing below the packer so that the interior of the tubing is sealed off. Hydraulic pressure is now applied from the surface to the tubing. The pressure is passed via ports 52 in the mandrel 1 to an annular space 53 between a cylinder 15 and a main piston 18. The main piston 18 is secured to the mandrel 1, and the cylinder 15 is initially secured in position 1 by five shear screws 24 acting on a lock mandrel 14.When the applied pressure reaches approximately 1100 psi, the shear screws 24 shear and the cylinder 15 is forced away from the piston 18, causing a lower cone 13 to force a row of slips 11 outwards to grip the casing.

Continued increase in pressure causes the mandrel 1 to move downwards because of the pressure applied to the piston 18 (and to any wireline blanking plug fitted) against bias provided by a spring 8 acting through a split sleeve 9. This action causes resilient packing elements 3 and 5 to be compressed between an upper gauge ring 2 and an upper cone assembly 7, and thus to expand into sealing engagement with the casing. The upper cone assembly 7 at the same time applies further expansion force to the slips 11. The packing elements 3 and 5, which are separated by spacers 4, are of conventional type well known in the art.

The packer is now set and can be tested by applying pressure down the upper annulus to prove that the packing elements 3 and 5 are not leaking. A body lock ring 16 has a serrated surface engaging the lock mandrel 14 to ensure that the cylinder 15 remains in position after the applied pressure is removed, so that all the setting forces are locked into the packer. The lock mandrel 14 is locked to the main body mandrel 1 by a shear wire 19.

The packer also includes a hold-down device which will now be described with particular reference to Figs. 1, 2 and 5. Three annular chambers 54a, 54b, 54c are formed around the mandrel 1. The first chamber 54a is formed between the upper gauge ring 2 and an upper cylinder 40. The second chamber 54b is formed between a first upper piston 36 and a piston housing 37. The third chamber 54c is formed between a second upper piston 36 and a collet slip cone 38. Each of the upper pistons 36 is secured on the mandrel 1 by a split ring retainer 35. The members 38, 37, 40 form a single assembly (in the present embodiment, being joined by wires 41 engaged in matching grooves) which is biassed downwardly by springs 39.

Fluid pressure from the well annulus below the set packer is communicated to the hold down device by means of two longitudinal passageways 55 and 56 (best seen in Figs. 2 and 5) which communicate with the chambers 54a-c via radial ports 58a-c, and with the annulus via radial ports such as 57 in the mandrel 1 and 59 in the upper cone 7. Sufficient clearance exists around the split sleeve 9 to allow fluid passage.

If pressure from below the set packer is higher than the pressure above it, the pressure differential acts on the three piston areas formed by the three chambers 54a-c to cause the assembly 38, 37, 40 to move upwardly. Fig. 1 shows the hold-down device in a condition where a first stage of such movement has occurred, with a split lock ring 32 abutting a shoulder of the mandrel 1. Further movement causes the collet slip cone 38 to force open a collet slip 34 into engagement with the casing, against a collet return force provided by spring 47.

The springs 39 define a minimum pressure differential which must be exceeded to initiate this action, suitably 100 - 200 psi.

Engagement of the collet slip 34 with the casing wall prevents the packer from being forced upwardly in the well casing by the action of high pressure in the lower annulus. It should be noted that the excess downhole pressure is actually transformed into a downward force on the mandrel because of the interaction of the collet slip 34 with the cone face 38.

An important feature of the present embodiment is that the three piston surfaces of the chambers 54a-c have a working area which is greater than the area of the engaged packing elements 3 and 5 plus the crosssectional area of the mandrel 1. This ensures that high pressure below the packer is always converted into a downwardly directed holding force. In one particular example, a 9.5/8" x 5.1/2" x 1/4" retrievable packer has a hold-down device piston area of 45 sq in. If the hold-down device were not present, pressure from below would strain the shear wire 19 with the possibility of prematurely unsetting the packer. Typically, the shear wire 19 will be rated at 50,000 lbs, and pressure from below in excess of 1,000 psi could strain it. With the hold-down device, the packer will hold at least 5,000psi from below without shearing the shear wire 19.

When the pressure differential is less than that set by the springs 39, the springs 39 relax and permit the packer to be unset and withdrawn.

To unset the packer, the tubing is picked up and a tension force in excess of 50,000 lbs is applied to the packer. This causes the shear wire 19 to shear and release the locked-in setting forces. The mandrel 1 moves upwardly relative to the slips 11, pulling the upper cone away from the slips 11. Continued upward movement allows the packing elements 3, 5 to relax and retract from the casing, and allows the spring 8 acting via split ring sleeve 9 to eject the lower cone 13 and cylinder 15; slip springs 12 then ensure full retraction of the slips 11.

If the collet slip 34 and collet slip cone 38 should remain lodged together and anchored to the casing, then continued upward movement will cause a shoulder 60 on the mandrel to engage split lock ring 32 and exert an upward pull on the collet slip 34, thus freeing any binding which may have occurred.

Prior to unsetting the packer it would be good practice to apply some upper annulus pressure at the wellhead; this would force the assembly 38, 37, 40 downwards and free any binding. Once free, the spring 47 and springs 39 will ensure that the collet slip 34 remains free.

As seen in Figs la and 2-4, the packer is provided with an access line 62 which allows a passage along the length of the packer for a 1/4" o.d. control line. The upper end of the access line 62 is provided with a control line extension nipple 26. As best seen in Fig.

2, the access line 62 and the passageways 55 and 56 extend parallel and in proximity to each other. To achieve this in a convenient manner with minimum loss of strength, the mandrel 1 is of eccentric form with its o.d. and i.d. offset to provide a thickened wall portion to accommodate the line 62 and passageways 55, 56.

The invention may equally be applied to resettable packers and to multistring packers, for example of the type described in our British Patent No. 2,238,811.

Other modifications may be made to the foregoing within the scope of the present invention.

Claims (9)

CZIAIMS

1. A downhole packer comprising a tubular body, gripping means disposed on the exterior of the tubular body and selectively operable to expand into gripping engagement with a surrounding casing to fix the tubular body in position in the casing, and sealing means disposed on the exterior of the tubular body and expandable into engagement with the casing to seal the annulus between the tubular body and the casing; and in which the gripping means includes force producing means operated in use by pressurised fluid tapped from said annulus at a point below said sealing means.

2. A downhole packer as claimed in Claim 1, wherein the gripping means comprises a first set of slips and a second set of slips, the first set of slips being operable by first piston means powered by pressurised fluid from within the tubular body, the first piston means also operating to produce expansion of the sealing means, and the second set of slips being operable by second piston means powered by said fluid pressure tapped from the annulus.

3. A downhole packer as claimed in Claim 2, wherein the second piston means has a surface area presented to said fluid pressure which is greater than the combined surface area of the exposed sealing means in the annulus and the end surface of the tubular member.

4. A downhole packer as claimed in Claim 2 or Claim 3, wherein the second piston means is in the form of a plurality of axially spaced annular piston elements disposed around the piston body.

5. A downhole packer as claimed in any one of Claims 2 to 4, wherein the second piston means includes spring means providing an initial bias force countering said fluid pressure.

6. A downhole packer as claimed in any one of the preceeding Claims, wherein said pressurised fluid is communicated from the annulus below the sealing means via one or more axial passageways in the wall thickness of the tubular member.

7. A downhole packer as claimed in Claim 6, wherein there are two axial passageways which are arranged parallel to an access line passageway extending along the tubular body.

8. A downhole packer as claimed in Claim 7, wherein the tubular body has a main through bore which is eccentric with respect to the exterior surface of the tubular body, thereby providing a thicker wall portion in which said passageways may be accommodated.

9. A downhole packer substantially as described in the accompanying specification, with reference to the drawings.