Cathodically-protected plug assembly

Abstract

A technique includes deploying a plug assembly including a degradable material inside a tubing string of a well; engaging the plug assembly with the tubing string to anchor the plug assembly to the tubing string; and preventing a cathodic reaction from degrading the degradable material. Preventing the cathodic reaction includes electrically isolating the engaged plug assembly from the tubing string. During the prevention of the cathodic reaction, a fluid barrier is formed in the tubing string using the plug assembly.

What is claimed is: 
     
         1 . A method comprising:
 deploying a plug assembly comprising degradable material inside a tubing string of a well;   engaging the plug assembly with the tubing string to anchor the plug assembly to the tubing string;   preventing a cathodic reaction from degrading the degradable material, wherein preventing the cathodic reaction comprises electrically isolating the engaged plug assembly from the tubing string; and   during the preventing of the cathodic reaction, forming a fluid barrier in the tubing string using the plug assembly.   
     
     
         2 . The method of  claim 1 , wherein deploying the plug assembly comprises deploying a tubular member having a though passageway and a seat to receive an untethered object to seal off the through passageway to form a fluid barrier inside the tubing string. 
     
     
         3 . The method of  claim 2 , further comprising:
 deploying the untethered object, wherein the untethered object comprises a degradable material having a relatively faster rate of degradation than the degradable material of the plug assembly.   
     
     
         4 . The method of  claim 1 , wherein:
 engaging the plug assembly with the tubing string comprises radially expanding a gripping member of the plug assembly; and   preventing the cathodic reaction comprises forming the gripping member from a dielectric material.   
     
     
         5 . The method of  claim 4 , wherein forming the gripping member from a dielectric material comprises forming the gripping member from a ceramic material. 
     
     
         6 . The method of  claim 1 , further comprising:
 radially expanding a sealing member of the plug assembly to form a fluid seal between the plug assembly and the tubing string;   wherein preventing the cathodic reaction comprises forming the sealing member from a dielectric material.   
     
     
         7 . The method of  claim 6 , wherein forming the sealing member from a dielectric material comprises forming the sealing member from an elastomer material. 
     
     
         8 . The method of  claim 6 , wherein forming the sealing member from a dielectric material comprises forming the sealing member from an electrically conductive material and coating the electrically conductive material with a dielectric material. 
     
     
         9 . A method comprising:
 running a plug assembly inside a tubing string of a well;   at a predetermined position in the tubing string, expanding a sealing element of the plug assembly and expanding an anchoring element of the plug assembly to cause the sealing element to engage a wall of the tubing string to form a fluid seal between a body of the plug assembly and the wall and to cause the anchoring element to engage the wall to secure the body to the wall;   using at least one material of the plug assembly to electrically isolate the plug assembly from the tubing string wall while the sealing element and the anchoring element are engaged with the tubing string wall to inhibit degradation of a degradable material of the plug assembly;   deploying an untethered object to land in the seat of the plug assembly to form a fluid barrier in the tubing string and performing a first downhole operation using the fluid barrier; and   subsequently performing a second downhole operation that relies on removal of the plug assembly due to removal of the at least one material and degradation of the degradable material of the plug assembly.   
     
     
         10 . The method of  claim 9 , wherein performing the first downhole operation comprises performing a hydraulic fracturing operation. 
     
     
         11 . An apparatus comprising:
 a body having a through passageway;   a sealing member having a contracted state and an expanded state to form a fluid seal between the body and an outer tubing;   an anchoring member having a contracted state and an expanded state in which the anchoring member secures the body to the outer tubing;   wherein the sealing member and the anchoring member electrically isolate the body from the outer tubing.   
     
     
         12 . The apparatus of  claim 11 , wherein the body comprises a degradable material to degrade at a relatively faster rate than a material of the outer tubing. 
     
     
         13 . The apparatus of  claim 11 , wherein the sealing member comprises an elastomer material. 
     
     
         14 . The apparatus of  claim 11 , wherein the sealing member comprises:
 an electrically conductive material; and   a coating to electrically isolate the conductive material from the body and the outer tubing.   
     
     
         15 . The apparatus of  claim 14 , wherein the coating comprises a material selected from the set of materials consisting essentially of:
 a Xylan impregnation coating, a Tellus 22 oil impregnation coating, a Tungsten Carbide coating, a Dykor coating, and a sol gel coating.   
     
     
         16 . The apparatus of  claim 11 , wherein the anchoring member comprises a ceramic material. 
     
     
         17 . The apparatus of  claim 11 , further comprising:
 a seal retainer adapted to axially translate in response to a force exerted by a setting tool to transition the seal member from the contracted to the expanded state and transition the anchoring member from the contracted state to the expanded state.   
     
     
         18 . The apparatus of  claim 16 , wherein the seal retainer comprises ratcheting teeth to lock the sealing member and the anchoring member in the contracted states. 
     
     
         19 . A system comprising:
 a tubing string; and   a plug assembly comprising:
 a body having a through passageway; 
 a sealing member having a contracted state and an expanded state to form a fluid seal between the body and an outer tubing; 
 an anchoring member having a contracted state and an expanded state in which the anchoring member secures the body to the outer tubing; 
   wherein the sealing member and the anchoring member electrically isolate the body from the outer tubing.   
     
     
         20 . The system of  claim 19 , wherein the tubing string comprises a casing. 
     
     
         21 . The system of  claim 19 , further comprising:
 an untethered object, wherein:
 the plug assembly comprises a seat to receive the untethered object to form a fluid barrier inside the tubing string; 
 the untethered object comprises a first degradable material having a first degradation rate; and 
 the plug assembly comprises a second degradable material having a second degradation rate less than the first degradation rate.