Sealing element of isolation device with inner core and outer shell

Abstract

A treatment operation can be performed in a wellbore. A zonal isolation device, such as a frac plug, can be set within a tubing string in the wellbore to isolate one zone from another zone. The plug can include a slip system and a sealing element located circumferentially around an inner mandrel of the plug. The sealing element can include an outer shell that surrounds an inner core. The outer shell can be made from a material having a high Young's modulus, while the inner core can have a very low Young's modulus. The outer shell can prevent premature deformation and expansion of the sealing element during run in. The outer shell and inner core can wholly or partially disintegrate in a desired a period of time after setting of the plug in the tubing string.

1 . A zonal isolation device comprising:
 a top slip;   a top slip prop in engagement with the top slip;   a bottom slip;   a bottom slip prop in engagement with the bottom slip;   an inner mandrel; and   a sealing element positioned between the top slip prop and bottom slip prop and located circumferentially around the inner mandrel, wherein the sealing element comprises:
 an inner core, wherein the inner core is made from a material having a Young's modulus less than 50 megapascals; and 
 an outer shell, wherein the outer shell surrounds the inner core, and wherein the outer shell is made from a material having a Young's modulus in the range of 500 to 300,000 megapascals, 
   wherein mechanical actuation of the sealing element causes the sealing element to create a seal against an inside of a casing string or tubing string.   
     
     
         2 . The device according to  claim 1 , wherein the isolation device is a frac plug, bridge plug, or zonal isolation plug. 
     
     
         3 . The device according to  claim 1 , wherein the outer shell has a bulk modulus in the range of 500 to 300,000 megapascals. 
     
     
         4 . The device according to  claim 1 , wherein the material of the outer shell has a Young's modulus selected such that structural integrity of the sealing element is maintained during run in. 
     
     
         5 . The device according to  claim 1 , wherein the outer shell is made from a material having a Young's modulus in the range of 20,000 to 120,000 MPa. 
     
     
         6 . The device according to  claim 1 , wherein the outer shell has a thickness, and wherein the thickness is in the range of 0.01 inches to 1 inch. 
     
     
         7 . The device according to  claim 1 , wherein the material of the outer shell is selected from pure metals, metal alloys, or composites. 
     
     
         8 . The device according to  claim 7 , wherein the pure metal or metal of the metal alloy is selected from the group consisting of magnesium, aluminum, tin, zinc, copper, beryllium, barium, manganese, and combinations thereof. 
     
     
         9 . The device according to  claim 7 , wherein the composite is an epoxy-based composite or structural molded phenolics. 
     
     
         10 . The device according to  claim 9 , wherein the epoxy-based composite is a glass fiber-reinforced epoxy composite or a carbon fiber-reinforced epoxy composite. 
     
     
         11 . The device according to  claim 1 , wherein at least a portion of the outer shell and the inner core are configured to disintegrate in a desired amount of time after the device is set within a tubing string. 
     
     
         12 . The device according to  claim 11 , wherein the disintegration occurs via degradation, dissolution, melting, or corrosion. 
     
     
         13 . The device according to  claim 1 , wherein the inner core is made from a material having a Young's modulus less than the Young's modulus of the material of the outer shell. 
     
     
         14 . (canceled) 
     
     
         15 . The device according to  claim 1 , wherein the material for the inner core is an elastomeric material, and wherein the elastomeric material is a polyurethane rubber or nitrile butadiene rubber. 
     
     
         16 . The device according to  claim 1 , wherein the inner core is a fluid, and wherein the fluid is a gel, semi-gel, or liquid. 
     
     
         17 . A method of isolating a zone of a subterranean formation comprising:
 (I) introducing a zonal isolation device within a tubing string of a wellbore that penetrates the subterranean formation, wherein the zonal isolation device comprises:
 (A) a top slip; 
 (B) a top slip prop in engagement with the top slip; 
 (C) a bottom slip; 
 (D) a bottom slip prop in engagement with the bottom slip; 
 (E) an inner mandrel; and 
 (F) a sealing element positioned between the top slip prop and bottom slip prop and located circumferentially around the inner mandrel, wherein the sealing element comprises:
 (i) an inner core, wherein the inner core is made from a material having a Young's modulus less than 50 megapascals; and 
 (ii) an outer shell, wherein the outer shell surrounds the inner core, and wherein the outer shell is made from a material having a Young's modulus in the range of 500 to 300,000 megapascals; and 
 
   (II) setting the isolation device at a desired location within the tubing string, wherein setting comprises mechanical actuation of the sealing element that causes the sealing element to create a seal against an inside of the tubing string.   
     
     
         18 . The method according to  claim 17 , wherein setting the isolation device comprises causing the sealing element to expand radially away from the inner mandrel to form a pressure tight annular seal. 
     
     
         19 . The method according to  claim 17 , wherein the outer shell has a thickness, and wherein the thickness of the outer shell is selected such that the outer shell maintains structural integrity to the sealing element during the step of introducing the zonal isolation device within the tubing string. 
     
     
         20 . The method according to  claim 17 , wherein at least a portion of the outer shell and the inner core are configured to disintegrate in a desired amount of time after the device is set within the tubing string. 
     
     
         21 . The method according to  claim 17 , wherein the material of the outer shell has a Young's modulus selected such that structural integrity of the sealing element is maintained during run in.