Rescue dart for pre-set frac plug and related methods

Abstract

A rescue dart for deployment down a wellbore to dislodge a pre-set frac plug having a plug mandrel from within the wellbore is provided. The rescue dart includes a dart body adapted to be conveyed down the wellbore via fluid flow and a mandrel defeater connected to the dart body and operable to reduce structural integrity of a portion of the plug mandrel until structural failure of the plug mandrel occurs and the frac plug is unset and dislodged. A corresponding system is also provided. The system includes the rescue dart and a pump for pumping fluids down the wellbore. A method of dislodging a pre-set frac plug using the rescue dart is also provided.

1 . A rescue dart for deployment down a wellbore to dislodge a pre-set frac plug comprising a plug mandrel from within the wellbore, the rescue dart comprising:
 a dart body adapted to be conveyed down the wellbore to the pre-set frac plug via fluid flow; and   a mandrel defeater connected to the dart body and operable to reduce structural integrity of a portion of the plug mandrel until structural failure of the plug mandrel occurs and the frac plug is unset and dislodged.   
     
     
         2 . The rescue dart according to  claim 1 , wherein the rescue dart is shaped and configured to operate in an engaged position where the dart body engages the pre-set frac plug and at least partially extends within an axial passage of the plug mandrel to position the mandrel defeater at a predetermined location along the axial passage. 
     
     
         3 . The rescue dart according to  claim 2 , wherein the dart body comprises a central segment, a dart head and a dart tail, the dart head being provided at a first end of the central segment, and the dart tail being provided opposite the dart head at a second end of the central segment, and wherein when in the engaged position, the dart tail abuts against the pre-set frac plug to prevent further forward movement of the rescue dart and position the dart body with respect to the pre-set frac plug. 
     
     
         4 . The rescue dart according to  claim 3 , wherein the dart tail is adapted to sit on a ball seat of the pre-set frac plug. 
     
     
         5 . The rescue dart according to  claim 3 , wherein the dart tail comprises at least one fluid passage for allowing fluid to flow through the dart tail and into the axial passage of the plug mandrel when the rescue dart is in the engaged position. 
     
     
         6 . The rescue dart according to  claim 5 , wherein the material of the mandrel defeater has a hardness which is greater than a hardness of the material of the plug mandrel. 
     
     
         7 . The rescue dart according to  claim 5 , wherein the central segment is a central tube comprising an inner conduit in fluid communication with the at least one fluid passage, and wherein the mandrel defeater comprises one or more fluid outlet ports extending through a thickness of the dart head for redirecting fluid flow towards the plug mandrel to at least partially cut the portion of the plug mandrel via fluid jetting. 
     
     
         8 . The rescue dart according to  claim 3 , wherein the mandrel defeater comprises at least one cutter blade operable between a retracted configuration where the cutter blade can be introduced within the axial passage, and an extended configuration for engaging and at least partially cutting the portion of the plug mandrel. 
     
     
         9 . The rescue dart according to  claim 8 , wherein the mandrel defeater further comprises an actuator adapted to operate the cutter blade in the extended configuration. 
     
     
         10 . The rescue dart according to  claim 3 , wherein the mandrel defeater is adapted to reduce structural integrity of the portion of the plug mandrel via heat. 
     
     
         11 . The rescue dart according to  claim 10 , wherein the central segment and/or dart head have an interior volumetric capacity, and wherein the mandrel defeater comprises heating material located within the capacity, and an actuator adapted to operate the heating material to heat up the plug mandrel. 
     
     
         12 . The rescue dart according to  claim 11 , wherein the actuator comprises an igniter adapted to heat up the heating material, and a firing pin operable to activate the igniter. 
     
     
         13 . The rescue dart according to  claim 10 , further comprising an interior volumetric capacity, and wherein the mandrel defeater comprises fuel located within the volumetric capacity, the mandrel defeater being adapted to release the fuel into the plug mandrel, causing the fuel to react with the fluids within the wellbore to melt at least one component of the plug. 
     
     
         14 . The rescue dart according to  claim 13 , wherein the mandrel defeater comprises a piston engaged within the capacity and movable towards the distal end via fluid flow to inject fuel into the plug mandrel. 
     
     
         15 . The rescue dart according to  claim 14 , wherein the mandrel defeater comprises a metering device adapted to adjust the flow rate of fluid against the piston for controlling an injection rate of fuel within the plug mandrel. 
     
     
         16 . The rescue dart according to  claim 15 , wherein the metering device is positioned within the dart body uphole of the piston, and forming therewith an internal chamber, the metering device comprising a passage defining a flow path to allow fluid to reach the internal chamber, the passage being shaped and sized to limit a flow rate of fluids therethrough. 
     
     
         17 . The rescue dart according to  claim 16 , wherein the passage has a tortuous configuration through the metering device to limit the flow rate of fluids. 
     
     
         18 . The rescue dart according to  claim 14 , wherein the dart head comprises a burst disk at a distal end thereof for containing the fuel within the volumetric capacity. 
     
     
         19 . A method of dislodging a pre-set frac plug comprising a plug mandrel from within a wellbore, the method comprising the steps of:
 deploying a rescue dart within the wellbore;   pumping fluid within the wellbore for conveying the rescue dart toward the pre-set frac plug via fluid flow;   engaging the rescue dart with the pre-set frac plug; and   operating the rescue dart to reduce structural integrity of a portion of the plug mandrel until structural failure of the plug mandrel occurs and the frac plug is unset and dislodged.   
     
     
         20 . The method according to  claim 19 , further comprising the step of monitoring pressure variations of the wellbore at surface. 
     
     
         21 . The method according to  claim 19 , further comprising the step of pumping the dislodged frac plug further downhole together with the rescue dart to allow resuming of fracturing operations. 
     
     
         22 . The method according to  claim 19 , wherein the rescue dart is as defined in  claim 1 .