Vented plug assemblies for wellbores

Abstract

Plug assemblies such as sealing devices comprise a vent tube disposed above the sealing device. The vent tube is selectively place in, and out of, fluid communication with a lower zone of a wellbore so that during curing of cement or other sealing material disposed on top of the sealing device, gas is permitted to flow from the lower zone to the surface of the wellbore. As a result, the likelihood of gas corrupting or otherwise leaking around the interface of the sealing element with the wall of the wellbore is decreased. After the cement has cured, fluid communication between the vent pipe and the lower zone is closed to isolate the lower zone from the upper zone disposed above the sealing device.

Description

BACKGROUND

1. Field of Invention

The invention is directed to plug assemblies for use in oil and gas wells and, in particular, a plug assemblies comprising a vent tube for venting during curing of cement or resin disposed on top of the plug assemblies.

2. Description of Art

Plug assemblies comprising sealing devices such as packers and bridge plugs for sealing wellbores are known in the art. For example, some sealing devices include an expandable sealing element such as a rubber casing or bladder or balloon that is inflated by fluid pumped down a tubing string. In certain of these sealing devices the rubber casing or bladder or balloon include swellable materials encased within an expandable sealing element such as a rubber casing or balloon are known in the art. These types of sealing devices expand and, thus, seal to the inner wall surface of a wellbore by contacting hydraulic fluid or other fluid with the swellable materials encased within the rubber casing so that the swellable materials absorb the fluid and expand. In one type of these sealing devices, for example, hydraulic fluid is pumped down a string of tubing having the sealing device secured thereto. The hydraulic fluid travels down the bore of the string of tubing and through a port that is in fluid communication with an inner cavity of the rubber casing. Swellable materials disposed within the rubber casing are contacted by the hydraulic fluid. As a result, the swellable materials absorb the fluid and expand. As the swellable materials expand and hydraulic fluid is pumped into the rubber casing, the rubber casing expands to seal the wellbore. After expansion, hydraulic fluid pressure is decreased and the rubber casing remains is held in the expanded position solely by the swellable materials having absorbed the fluid.

Regardless of how the sealing device is deployed in the wellbore, in certain applications the sealing device is secured in place to form a “permanent” plug of the wellbore by disposing a sealing material such as cement, resin, or other material on top of the sealing device. The sealing material is used in an attempt to stop gas percolation in the wellbore. Gas percolation occurs when a gas disposed below the sealing device “leaks” or migrates around the sealing element, such as through irregularities in the casing of the wellbore to which the sealing device is contacted. Although the sealing material is placed on top of the sealing device to prevent the gas from traveling to the surface of the well, sometimes, the gas creates a path through the uncured sealing material causing a leak path to be formed and, therefore, undermining the effectiveness of the sealing device to completely isolate the zone of the wellbore disposed below the sealing device.

SUMMARY OF INVENTION

Broadly, the sealing devices disclosed herein include a vent tube disposed above the sealing device to keep cement, resin, or other sealing material from being compromised by gas percolation during curing of the cement, resin, or other sealing material. The vent tube comprises a bore that is in fluid communication with the bore of a sealing device, the bore of an on-off connector and the bore of a tubing string connected to the on-off connector. In one embodiment, the sealing device includes valve such as a removable plug so that the bore of the sealing device can be selectively opened and closed to flow through the sealing device to the portion of the wellbore disposed below the sealing device, i.e., the lower zone. The removable plug is initially disposed in the sealing device, or the valve is initially in its closed position, so that there is no fluid communication through the sealing device to the lower zone. As a result, fluid within the bores of the tubing string actuates the sealing device so that the sealing element of the sealing device engages the wall of the wellbore to isolate the wellbore into upper and lower zones. The upper zone is the portion of the wellbore disposed above the sealing device and, as mentioned above, the “lower zone” is the portion of the wellbore disposed below the sealing device.

In one particular embodiment, a lower sub comprising the valve, e.g., removable plug is attached to the lower end of the sealing device.

In operation, the sealing device is secured to a tool string that comprises a vent tube releasably secured to the upper end of the sealing device, an on-off connector releasably secured to the upper end of the vent tube, and tubing releasably secured to the upper end of the on-off connector. In one particular embodiment, a lower sub is releasably secured to the lower end of the sealing device. The tool string is then run to depth in the wellbore and the sealing device is actuated, e.g., inflated or expanded such as through application of fluid pressure and pressure, to set the sealing device within the wellbore. After actuation, fluid communication between the bore of the sealing device and the lower zone is established such as by opening a valve in the sealing device or in the lower sub, or removing a plug previously disposed within the bore of the sealing device or the lower sub. After such fluid communication is established, a flow path is created between the lower zone and the surface of the wellbore. Thus, the vent tube permits gas to “vent” or flow from the lower zone to the upper zone and, thus, to the surface of the wellbore.

Thereafter, cement, resin, or other sealing material is disposed on top of the sealing device and around the vent tube such as by using a small string of pipe pumping the sealing material around an annulus formed by the vent tube and the wellbore wall. The sealing material is permitted to cure. During this time period, gas is permitted to flow from the lower zone to the upper zone through the tubing. Because of the fluid communication between the lower zone through the vent tube, the probability of gas migrating around the sealing element of the sealing device is lessened because the gas is permitted to flow through the vent tube instead of having to force its way around the sealing element. After the sealing material has cured, the removable plug is reinstalled, or the valve closed and the on-off connector is actuated to release the tool string from the vent tube leaving a permanent installation that isolates the lower zone from the upper zone.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial cross sectional view of wellbore comprising one specific embodiment of the sealing device with vent tube disclosed herein.

While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION

Referring now to FIG. 1, one specific embodiment of sealing device 60 is described broadly with respect to wellbore 10 disposed within formation 12 having casing string or casing 14 disposed therein. Sealing device 60 is secured to tool string 100 and run-in and set (as shown in FIG. 1). Broadly, tool string 100 comprises lower sub 30, vent tube 40, and on-off connector 50, and sealing device 60.

Lower sub 30 comprises upper and lower ends, bore 32, and removable plug 34. Upper end is releasably secured to the lower end of sealing device 60 so that bore 32 is in fluid communication with bore 62 of sealing device 60 (discussed in greater detail below).

Vent tube 40 comprises one or more joints of tubing releasably secured to the upper end of sealing device 60. Vent tube 40 comprises vent tube bore 42 in fluid communication with sealing device bore 62 and bore 52 of on-off connector 50.

In the embodiment of FIG. 1, sealing device 60 is an inflatable-type sealing device comprising a bore 62 in fluid communication with an interior area (not shown) of sealing element 64. In operation of setting sealing device 60, tool string 100 is assembled and run to depth within wellbore 10. Fluid (not shown) is pumped down a bore of tool string 100, through bore 52 of on-off connector, through bore 42 of vent tube 40, into bore 62 of sealing device and into bore 32 of lower sub 30. During run-in and actuation of sealing device 60, removable plug 34 is disposed within bore 32 of lower sub 30 so that fluid pumped down the bore of tool string 100 flows from bore 32 into the interior area of the sealing element 34 to inflate and set sealing device 30 within wellbore 10. In other words, removable plug 34 prevents fluid flowing down tool string 100 during actuation of sealing device 60 from flowing out of the lower end of lower sub into lower zone 18 of wellbore 10. Actuation of sealing device 60 isolates the portion of wellbore 10 disposed below sealing device 60, referred to herein as lower zone 18 from the portion of wellbore 10 disposed above sealing device 60, referred to herein as upper zone 20.

After sealing device 60 is actuated to its set position, fluid pressure is “backed-off” or reduced and removable plug 34 is removed from bore 32 of lower sub 30 (as shown in FIG. 2) such as by running a tubing string (not shown) down through the bore of tool string 100, through on-off connector bore 52, vent tube bore 42, sealing device bore 62, and into lower sub bore 32. Thus, as shown in FIG. 2, fluid communication is established between lower zone 18 and the surface of wellbore 10.

After removable plug 34 is removed, cement, resin, or other sealing material 24 (FIG. 2) is disposed on top of sealing device 60 within annulus 22 (shown in FIG. 1) defined by the space between the outer wall surface of vent tube 40 and inner wall surface 15 of casing 14. The amount of sealing material disposed on top of sealing device 60 can be modified as desired by the operator, provided however, that the amount of sealing material does not rise so high that on-off connector 50 cannot operate. Thereafter, the sealing material is permitted to cure through any method known in the art. During the curing step, gas disposed in lower zone 18 is permitted to flow through bore 32, sealing device bore 62, vent tube bore 42, on-off connector bore 52, and through the bore of tool string 100 to the surface of wellbore 10 (FIG. 2).

Referring now to FIG. 3, after the sealing material has cured, removable plug 34 is reinstalled within bore 32 such as by running a tubing string (not shown) down through the bore of tool string 100, through on-off connector bore 52, vent tube bore 42, sealing device bore 62, and into lower sub bore 32. Thereafter, on-off connector 50 is actuated to disconnect from vent tube 40 leaving sealing device 60 secured in place within wellbore 10 such that upper zone 20 is isolated from lower zone 18 as shown in FIG. 3.

It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. For example, a removable plug may be a valve that can be actuated from the surface of the wellbore. Additionally, the sealing device may include the valve, e.g., removable plug, such that lower sub is not needed. Further, on-off connector may be any device known in the art that is capable of releasing the connection between the on-off connector and the vent tube. Moreover, the sealing device is not required to be an inflatable-type sealing device. Instead, it can be a “swellable-type” sealing device or any other type of sealing device known in the art. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.

Claims

1. A plug assembly for installation into a wellbore, the plug assembly comprising:

a sealing device comprising a sealing element, sealing device bore, the bore being in fluid communication with the sealing element at a first location and the bore being in fluid communication with a valve at a second location, wherein the first location is disposed above the second location;

a vent tube comprising a vent tube bore in fluid communication with the sealing device bore, the vent tube being disposed above the sealing device; and

a release assembly comprising a release assembly bore in fluid communication with the vent tube bore, the release assembly being releasably connected to the vent tube.

2. The plug assembly of claim 1, wherein the valve is disposed within a lower sub-assembly disposed below the sealing device, the lower sub-assembly comprising a lower sub-assembly bore, the valve being disposed within the lower sub-assembly bore.

3. The plug assembly of claim 2, wherein the valve comprises a removable plug.

4. The plug assembly of claim 1, wherein the vent tube comprises two or more joints of tubing.

5. The plug assembly of claim 1, wherein the sealing element comprises at least one swellable material.

6. The plug assembly of claim 1, wherein the sealing element comprises an inflatable bladder.

7. A method of installing a plug to a wellbore, the method comprising the steps of:

(a) assembling a tubing string comprising a release assembly comprising a release assembly bore, the release assembly being releasably connected to a vent tube comprising a vent tube bore, the vent tube being connected to a sealing device comprising a sealing device bore, the release assembly being disposed above the vent tube and the vent tube being disposed above the sealing device, the release assembly bore, vent tube bore, and sealing device bore each being in fluid communication with each other and in fluid communication with a valve;

(b) running the tubing string into a wellbore to a desired location;

(c) disposing the valve in a closed position;

(d) pumping fluid down the tubing string to actuate the sealing device causing a sealing element of the sealing device to engage an inner wall surface of the wellbore;

(e) disposing the valve in an opened position;

(f) disposing a sealing material on top of the sealing device in an annulus formed by an outer wall surface of the vent tube and the inner wall surface of the wellbore;

(g) allowing the sealing material to cure;

(h) disposing the valve in the closed position; and

(i) actuating the release assembly to disconnect the tubing string from the vent tube and remove the tubing string from the wellbore.

8. The method of claim 7, wherein the valve comprises a removable plug and step (e) is performed by running a tool string down the bores of the release assembly, vent tube, and sealing device to engage the removable plug and retracting the tool string from the bores of the release assembly, vent tube, and sealing device.

9. The method of claim 8, wherein step (h) is performed by running a tool string down the bores of the release assembly, vent tube, and sealing device to dispose the removable plug in the sealing device bore and retracting the tool string from the bores of the release assembly, vent tube, and sealing device.