Staged Actuation Shear Sub for Use Downhole

Abstract

A shear assembly used downhole to actuate a work string function includes a dampening subassembly to dampen the momentum of moving parts following shearing to avoid excessive acceleration and resulting jarring forces within the work string. A dual shear assembly is provided, in which the dampening subassembly prevents inertial force resulting from a first shear from exceeding the threshold for actuating the second, higher threshold, shear mechanism thereby allowing more precise control of the forces applied to the work string to prevent premature shearing of the second shear mechanism. In a specific embodiment, the dampening subassembly is a hydraulic dampening subassembly. The dual shear assembly may be used, for example, to first open a wash port above a tool lodged within the wellbore to loosen debris above the lodged tool, and then to shear the tool from the work string if necessary.

1 . A shear assembly for use downhole, the shear assembly comprising:
 a. a mandrel for integration within a work string;   b. a shear sleeve slideable with respect to the mandrel to actuate a work string function;   c. setting means for setting the shear sleeve in a fixed position with respect to the mandrel, the setting means shearable by application of a threshold force to the work string, thereby actuating the work string function; and   d. a dampening subassembly operatively associated with the mandrel and with the shear sleeve for slowing the sliding momentum of the shear sleeve with respect to the mandrel following shearing of the setting means.   
   
   
       2 . A multiple shear assembly for use downhole, the shear assembly comprising:
 a. a mandrel for integration within a work string;   b. a first shear sleeve slideable with respect to the mandrel to actuate a first work string function;   c. first setting means for setting the first shear sleeve in a fixed position with respect to the mandrel, the first setting means shearable by application of a first threshold force to the work string, thereby actuating the first work string function;   d. a second shear sleeve slideable with respect to the mandrel to actuate a second work string function;   e. second shearable setting means for setting the second shear sleeve in a fixed position with respect to the mandrel, the second setting means shearable by application of a second threshold force to the work string, thereby actuating the second work string function; and   f. a dampening subassembly operatively associated with the mandrel and with the first shear sleeve for slowing the sliding momentum of the mandrel with respect to the first shear sleeve following shearing of the first setting means.   
   
   
       3 . The assembly as in  claim 2  wherein the first work string function is actuated upon abutment of a mandrel surface with a shear sleeve surface, and wherein the dampening subassembly slows the sliding momentum of the mandrel to limit the force of said abutment. 
   
   
       4 . The assembly as in  claim 3  wherein the force of abutment is limited to a value less than the second threshold force. 
   
   
       5 . The assembly as in  claim 2 , wherein the dampening subassembly is a hydraulic dampening subassembly. 
   
   
       6 . The assembly as in  claim 5 , wherein the hydraulic dampening subassembly comprises one or more annular pistons disposed within hydraulic chambers operatively attached to the mandrel. 
   
   
       7 . The assembly as in  claim 6  wherein the hydraulic chambers are filled with a hydraulic fluid of suitable viscosity to provide the desired degree of dampening. 
   
   
       8 . The assembly as in  claim 3  wherein the dampening subassembly reduces the abutment force by at least, 10,000 pounds force. 
   
   
       9 . The assembly as in  claim 2  wherein the second threshold force exceeds the first threshold force by more than 15%. 
   
   
       10 . The assembly as in  claim 2 , wherein the work string includes a frac packer, and wherein the first threshold force is at least 40,000 pounds force. 
   
   
       11 . The assembly as in  claim 10  wherein the second threshold force is less than 96000 pounds. 
   
   
       12 . The assembly as in  claim 10  wherein the second threshold force is greater than 56000 pounds. 
   
   
       13 . The assembly as in  claim 2  wherein the first work string function is opening of a wash port within the work string. 
   
   
       14 . The assembly as in  claim 2  wherein the second work string function is shearing of the mandrel from the work string. 
   
   
       15 . The assembly as in  claim 14 , wherein said shearing of the mandrel from the work string exposes a fishneck for use in recovery of the mandrel from the wellbore. 
   
   
       16 . A method for returning a work string to surface when a downhole tool within the work string has become lodged within the wellbore, the method comprising the steps of:
 a. opening a wash port within the work string above the lodged tool;   b. circulating fluid within the work string and the wellbore above the lodged tool to loosen debris from above the lodged tool; and   c. pulling the work string and tool to surface.   
   
   
       17 . The method as in  claim 16 , further comprising the step of shearing a first shearable setting means within the work string to open the wash port. 
   
   
       18 . The method as in  claim 16 , further comprising the step of shearing the lodged tool from the work string.