STAGED ACTUATION SHEAR SUB FOR USE DOWNHOLE

摘要

A shear assembly is disclosed which may be used downhole to actuate a work string function. The shear assembly 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. In other words, the dampening subassembly allows more precise control of the forces applied to the work string to prevent premature shearing of the second shear mechanism, even when the difference between the two shear thresholds is minimal. 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.