Downhole Release Mechanism

Abstract

A downhole release mechanism for a drillstring. A first, uphole section and a second, downhole section comprise longitudinal bores and are rotationally locked together via a spline. A collet assembly is connected to the first section, with collet fingers extending into the bore of the second section when the first and second sections are joined. The collet fingers are biased outwardly, and an external shoulder on the collet fingers mates with an internal shoulder in the second section, locking the sections together. A piston is slidably disposed in a bore of the collet, and spring biased uphole. Fluid flow moves the piston to a downhole position, in which the collet fingers are held outwardly and the shoulders locked together. With fluid flow stopped, the piston moves uphole, and sufficient tension on the mechanism shears shear screws and snaps the collet fingers out the internal shoulder, releasing the mechanism.

We claim: 
     
         1 . A downhole release mechanism, comprising:
 a first, uphole section and a second, downhole section, said first and second sections comprising tubular members with longitudinal bores, and a spline connection rotationally locking said first and second sections together when said first and section sections are joined;   a collet assembly attached to said first section and having a plurality of flexible collet fingers extending into said second section when said first and second sections are joined, said collet fingers comprising an external shoulder, said collet fingers being biased radially outward;   said second section comprising an internal shoulder in said longitudinal bore, said internal shoulder shaped so as to receive said external shoulder of said collet fingers;   a piston slidably disposed in a bore of said collet assembly and spring biased toward a first, uphole position, said piston movable to a second, downhole position within said collet fingers by fluid flow through a bore of said piston, whereby when said first and second sections are joined and said collet is positioned within said second section, and said piston is in said second, downhole position, said collet fingers are held radially outward such that said external shoulder on said collet fingers and said internal shoulder in said second section are engaged, thereby locking said first and second sections together.   
     
     
         2 . The downhole release mechanism of  claim 1 , further comprising one or more shear screws joining said first and second sections. 
     
     
         3 . The downhole release mechanism of  claim 1 , wherein said piston comprises a removable jet in said bore of said piston. 
     
     
         4 . The downhole release mechanism of  claim 1 , wherein said second section comprises an internal profile adapted to engage a fishing tool. 
     
     
         5 . The downhole release mechanism of  claim 1 , further comprising a pressure relief disk permitting fluid flow from said bore of said downhole release mechanism to an annulus around said downhole release mechanism, once a desired pressure differential across said pressure relief disk has been attained. 
     
     
         6 . The downhole release mechanism of  claim 2 , wherein said piston comprises a removable jet in said bore of said piston. 
     
     
         7 . The downhole release mechanism of  claim 6 , wherein said second section comprises an internal profile adapted to engage a fishing tool. 
     
     
         8 . The downhole release mechanism of  claim 7 , further comprising a pressure relief disk permitting fluid flow from said bore of said downhole release mechanism to an annulus around said downhole release mechanism, once a desired pressure differential across said pressure relief disk has been attained. 
     
     
         9 . The downhole release mechanism of  claim 2 , wherein when fluid flow through said piston stops, said piston moves under said spring bias to said first, uphole position out of engagement with said collet fingers, and with sufficient tension on said downhole release mechanism said collet fingers move radially inward and said external shoulder on said collet fingers snaps out of engagement with said internal shoulder in said second section, said shear screws shear and said first and second sections separate. 
     
     
         10 . A downhole release mechanism, for placement in a drillstring, comprising:
 a first, uphole section and a second, downhole section, said first and second sections comprising tubular members with longitudinal bores, and a spline connection rotationally locking said first and second sections together when said first and section sections are joined, said second section comprising an internal profile adapted to engage a fishing tool;   one or more shear screws joining said first and second sections;   a collet assembly attached to said first section and having a plurality of flexible collet fingers extending into said second section when said first and second sections are joined, said collet fingers comprising an external shoulder, said collet fingers being biased radially outward;   said second section comprising an internal shoulder in said longitudinal bore, said internal shoulder shaped so as to receive said external shoulder of said collet fingers;   a piston slidably disposed in a bore of said collet assembly and spring biased toward a first, uphole position, said piston movable to a second, downhole position within said collet fingers by fluid flow through a bore of said piston, said piston further comprising a removable jet in the bore thereof, whereby when said first and second sections are joined and said collet is positioned within said second section, and said piston is in said second, downhole position, said collet fingers are held radially outward such that said external shoulder on said collet fingers and said internal shoulder in said second section are engaged, thereby locking said first and second sections together; and   a pressure relief disk permitting fluid flow from said bore of said downhole release mechanism to an annulus around said downhole release mechanism, once a desired pressure differential across said pressure relief disk has been attained.   
     
     
         11 . The downhole release mechanism of  claim 10 , wherein said external shoulder on said collet fingers and said internal shoulder in said second section are angled so as to withstand a desired tension between said first and second sections before said collet fingers move radially inward. 
     
     
         12 . The downhole release mechanism of  claim 11 , wherein when fluid flow through said piston stops, said piston moves under said spring bias to said first, uphole position out of engagement with said collet fingers, and with sufficient tension on said downhole release mechanism said collet fingers move radially inward and said external shoulder on said collet fingers snaps out of engagement with said internal shoulder in said second section, said shear screws shear and said first and second sections separate. 
     
     
         13 . The downhole release mechanism of  claim 11 , wherein said piston comprises an angled nose at its downhole end, shaped to engage a mating profile within said collet fingers, and wherein said piston comprises a reduced outer diameter section proximal said angled nose. 
     
     
         14 . The downhole release mechanism of  claim 13 , wherein said piston further comprises guide members of a low-friction material, positioned on an outer surface thereof.