Casing Plug

Abstract

A dissolvable plug for plugging oil and gas well casings to perform treatment and other downhole operations is disclosed. The plug is attached to a setting tool and lowered downhole. The setting tool is fired to cause the plug to engage the casing and to release the setting tool. A ball is dropped to close the passage through the plug. Hydraulic pressure is applied on the ball from above and the plug expands outwards to create a seal between the plug and the casing. After operations above the plug are completed, the ball and the plug are dissolved by the surrounding fluids.

Description

RELATED PRIORITY DATE APPLICATION

This application claims the benefit under 35 U.S.C. 119(e) of the U.S. provisional application No. 62/691,588 filed on Jun. 28, 2018.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of oil tools for the completion of oil and gas oils and, more particularly, to the field of casing plugs. Still more particularly, the present invention discloses a casing plug constructed of dissolvable material so that the plug may be dissolved after it is used downhole to reestablish communication above and below the plug without mechanical intervention from the surface.

BACKGROUND OF THE INVENTION

The use of plugs and packers in downhole oil and gas operations are well known. During completion or well intervention, a plug is used to isolate a part of the casing from another part. For instance, when a job is carried out on the upper section of the well, the lower part of the interior of the casing must be isolated and plugged, i.e. zonal isolation in a well. Plugs can be temporary or permanent; the former can be retrieved, whereas the latter have to be drilled out. Plugs can he set using a wire-line, coiled tubing or drill pipe.

One disadvantage of the plugs presently used is that they require mechanical intervention from above to retrieve them or to drill through them to reestablish flow through the casing. These practices cause delays and additional expenses.

According to the present invention, a dissolvable plug is disclosed which can be dissolved downhole following completion of the operations to reestablish the flow through the casing without requiring mechanical intervention from above to retrieve or to drill the plug.

These and other advantages of the present invention will become apparent from the following description.

SUMMARY OF THE INVENTION

A dissolvable plug for plugging oil and gas well casings to perform treatment and other downhole operations is disclosed. The plug includes an upper sub, a lower sub and a slip assembly. The upper sub includes a flow passage with a tapered mouth, and a circumferential exterior ramp.

The lower sub includes an axial bore. The slip assembly has a chamfered end and ceramic buttons on its exterior and is disposed over the upper sub. In the assembled position, the slip assembly is slidingly disposed over the upper sub and its chamfered end intimately engages the ramp on the exterior of the upper ramp. The lower end of the upper sub is received in the upper end of the bore of the lower sub. The lower sub is connected to the upper sub by shear screws.

In operation, the plug is attached to a wireline setting tool which includes a setting tool sleeve, a setting tool adopter and a shear adapter by shear screws connecting the shear adopter to the lower sub. The setting tool and the attached plug are lowered downhole to be set at the desired location inside the casing.

When the plug reaches the desired setting depth in the casing the setting tool is fired. The setting sleeve holds the upper sub in place while the shear adapter pulls up the lower sub causing the shear screws connecting the upper sub to the lower sub to shear. As the lower sub is pulled upwards, it causes the slip assembly to expand outwards and to engage the casing. In that position, the lower sub becomes locked to the upper sub by locking threads. Then, the remaining setting force shears screws connecting the shear adapter to the bottom sub and the setting tool is released and raised to the surface.

After the setting tool is raised to the surface, a ball is pumped downhole to rest in tapered mouth of the upper scab and to close the passage therethrough. Pressure is applied on the ball to extrude outwards the upper portion of the upper sub thereby tightening the seal against the casing. The zone inside the casing above the plug is now isolated and various perforations and treatment operations are performed therein.

The plug and the ball are constructed of material which are dissolvable after a certain amount of time following exposure to the surrounding fluids, the amount of time being depended on the temperature and salinity of the liquids. After the treatment operations are completed, the plug and the ball begin to dissolve thereby reopening the passage through the casing without intervention from the surface to remove the plug. Preferred dissolvable material are magnesium alloys and degradable sealing elements. Other dissolvable material may be used to construct the plug and the ball

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiment of the invention, reference will now be made to the accompanying drawings wherein:

FIG. 1 is a cross sectional view of a plug made in accordance of the present invention along the axis A-A of the plug of FIG. 3;

FIG. 2 is a perspective view of the plug of FIG. 1;

FIG. 3 is a bottom view of the plug of FIG. 1;

FIG. 4 is a cross sectional view of the plug of FIG. 1 attached to a setting tool;

FIG. 5 is a perspective view of the plug and setting tool of FIG. 4; and

FIG. 6 is a cross sectional view of the plug of FIG. 1 following activation providing a seal in a casing downhole.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 there is shown a plug 10 that includes an upper sub 12, a lower sub 14 and a slip assembly 16. Upper sub 12 includes an internal axial flow passage 20 with a tapered mouth 22, an exterior circumferential groove 24 adjacent to mouth 22, a circumferential exterior ramp 26, a plurality of radial screw sockets 28 and a plurality of grooves 32 circumferentially disposed over the lower portion of upper sub 12. Upper sub 12 further includes an upper sub locking thread (not shown) on its exterior surface that will engage a corresponding lower sub locking thread in lower sub 14 when lower sub 14 is moved to a locking position as described below. An elastomeric ring 36 is disposed in circumferential groove 24.

Lower sub 14 includes an axial bore 36, a plurality of radial screw sockets 38 circumferentially disposed in the upper portion of lower sub 14, and a plurality of radial screw sockets 42 circumferentially disposed in the lower portion of lower sub 14. Lower sub 14 further includes a lower sub locking thread (not shown) on its interior wall of bore 36 which is lockingly engageable with the upper sub locking thread when lower sub 14 is moved to a locking position.

Slip assembly 16 is a generally tubular member having a chamfered end 46 and a plurality of ceramic buttons 56 drilled in the exterior thereof. In the assembled position slip assembly 16 is slidingly disposed over the lower portion of upper sub 12 and chamfered end intimately engages conforming ramp 16. The lower end of upper sub 12 is intimately received in the upper end of bore 36 to align screw sockets 28 and 38. Shear screws 50 are inserted in sockets 28 and 38 to securely connect upper sub 12 to lower sub 14.

Referring now to FIG. 2 there is shown a perspective view of plug 10 having an upper sub 12, a lower sub 14 with radial screw sockets 42 and a slip assembly 16 having buttons 56.

Referring now to FIG. 3, there is shown a bottom view of plug 10 in the assembled position having lower sub 14 with radial screw sockets 42 and upper sub 12 received in lower sub 14.

Referring now to FIG. 4, plug 10 is attached to a wireline setting tool 60 such as a Baker 10 setting tool. Setting tool 60 includes a setting tool sleeve 62 abutting the top of upper sub 12, a setting tool adapter 64 and a shear adapter 70 having screw sockets 72. Screw sockets 72 are aligned with radial screw sockets 42 and shear screws 74 are inserted therein to securely connect shear adapter 70 to lower sub 14. Plug 10 attached to setting tool 60 is lowered downhole to be set at the desired location inside the casing. Referring now to FIG. 5 there is shown a perspective view of setting tool connected to plug 10.

Referring back to FIG. 4, when plug 10 reaches the desired setting depth in a casing, setting tool 60 is fired. Setting sleeve 62 holds upper sub in place while shear adapter 70 pulls up lower sub 14 up causing shear screws 50 to shear. As lower sub 14 is pulled upwards, it advances slip assembly 16 to ride on ramp 26 whereby it is pushed outwards to engage the casing. In that position, the lower sub locking thread and the upper sub locking thread described above are lockingly engaged. After slip assembly 16 engages the casing and the two locking threads engage each other, the remaining setting force shears screws 74 that hold shear adapter 70 to bottom sub 14 and setting tool 60 is released and raised to the surface.

Referring now to FIG. 6, there is shown plug 10 with slip assembly 16 engaging a casing 78. After setting tool 60 (not shown) is raised to the surface a ball 80 is pumped downhole to rest in tapered mouth 22 inside upper sub 12 and to close passage 20. Pressure is applied on ball 80 to extrude outwards the upper portion of upper sub 12 thereby tightening the seal against casing 78. The zone inside casing above plug 10 is now isolated and various perforations and treatment operations are performed therein. As shown, plug 10 is designed to hold pressure from above only.

According to the present invention, plug 10 and ball 80 are constructed of material which are dissolvable after a certain amount of time when they are exposed to the fluids flowing in the zone during the treatment operations. The amount of time after which the material begins dissolving depends on the temperature and salinity of the water downhole around plug 10. According to the invention, after the treatment operations are completed, plug 10 and ball 80 begin to dissolve and the seal to casing 78 is lost whereby more fluid flows through and around plug 10 and ball 80 further effecting and completing the dissolution of plug 10 and ball 80. Accordingly, because plug 10 and ball dissolve, no intervention from the surface is required to remove plug 10. The material are selected so as to begin dissolving after a certain time, preferably after 24 to 48 hours, following the start of the perforation and treatment operations downhole in the zone above plug 10.

Preferred dissolvable material are dissolvable magnesium alloys such as the ones being sold by Bubbletight under the trademark Magnalloy and degradable sealing elements sold also by Bubbletight. It should be understood, however, that other dissolvable material may be used to construct plug 10 and ball 80 as long as they can withstand the pressures downhole while conducting the operations in the zone above plug 10.

The locking screws are preferably constructed of brass material. Further, instead of ceramic buttons 56, slips with wickers or bi directional slip may be used on slip assembly 16.

While the invention is described with respect to specific embodiments, modifications thereof can be made by one skilled in the art without departing from the spirit of the invention. The details of said embodiments are not to be construed as limitations except to the extent indicated in the following claims.

Claims

1. A plug for sealing a casing having an inner surface, comprising:

a first member having a sealing member;

a slidable second member connected to the first member; and

a third member slidable over the first member;

the first, second and third members being dissolvable after a certain amount of time.

2. A plug for sealing a casing having an inner surface, comprising:

a first member having a sealing member; and

a slidable second r connected to the first member;

the first, second and third members being dissolvable after a certain amount of time.