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.

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.