Staged actuation shear sub for use downhole

The present invention claims the benefit of U.S. Provisional Patent Application Ser. No. 61/012,457 entitled “Staged Actuation Shear Sub for Use Downhole” filed Dec. 9, 2007.

The present invention relates generally to tools for use within a wellbore. More particularly, the present invention relates to a shear assembly for integration within a work string.

During use of downhole equipment within a wellbore, sand and other debris may enter the wellbore and accumulate above the bottom hole assembly. From time to time, the tool may become lodged within the wellbore due to this accumulation of debris. Various means of attempting to loosen lodged equipment are known, which generally include pulling (such as the controlled pulling taught by U.S. Pat. No. 7,249,633), vibrating, or reciprocating the bottom hole assembly within the wellbore until same is freed of debris. Unfortunately, these loosening methods often fail, requiring the bottom hole assembly to be sheared from the tubing string and fished out of the well. Such fishing operations are expensive and time consuming, as an independent contractor must transport specialized equipment to the site in order to fish the bottomhole assembly from the wellbore.

Once the tubing string has been sheared from the fishneck, the fishneck may remain inaccessible due to further accumulation of debris during shearing and removal of the tubing string. Accordingly, fishing/pulling equipment may incorporate a wash feature in order to loosen debris from about the fishing neck of a lodged downhole tool (see for example U.S. Pat. No. 3,020,957; U.S. Pat. No. 4,749,044; and U.S. Pat. No. 5,887,925).

Similarly, U.S. Pat. No. 6,352,113 describes a submersible pump assembly for attachment within a tubing string, the pump assembly having a fluid tube extending from surface down to the bottom hole assembly to loosen debris from above the upper packer prior to pulling the bottom hole assembly from the wellbore.

To date, a shear-actuated wash mechanism has not been incorporated within a work string above a bottom hole assembly for use in freeing the bottom hole assembly should it become lodged within the wellbore. Moreover, it has not to date been possible to include two tension shear-actuated devices within a work string in close proximity, or with similar shear thresholds.

It is, therefore, desirable to provide a simple, staged device for washing the area above a bottom hole assembly to free lodged equipment, and to shear the bottomhole assembly from the coiled tubing should the wash be ineffective in releasing the tool from the wellbore.

In addition to the desire for a tool able to clear debris from above lodged downhole equipment, there is a more general need to provide a staged means of actuating downhole equipment or processes. Although tension shear devices are among the most simple means of tool actuation, the shearing of pins to actuate, open, or slideably operate an otherwise fixed element is generally avoided due to the unpredictable inertial forces that result from the application and release of tension within the coiled tubing. In other words, application of pulling force to the tubing string over a great vertical distance causes the coiled tubing to stretch. Thus, when the shearable element is released upon application of an appropriate threshold force at the shear location, the sheared element will generally slide forcibly into a corresponding shoulder. This inertial force may be magnified by the simultaneous release of tension within the extended or stretched coiled tubing. Should a second tension-shearable element be present in close proximity within the work string, the inertial force of the moving parts immediately subsequent to the first shearing event may be great enough to exceed the second shear threshold unintentionally.

Due in part to the above-noted limitations associated with current shear devices, typically only one tension shear-actuated function is useful within a tubing string. As such, a shear sub is usually limited to use as a last resort mechanism by which the operator may separate the tubing string from the equipment in an emergency or otherwise problematic situation.

It is therefore further desirable to provide a shear assembly in which recoil force may be minimized or dampened, as this may facilitate development of a dual or multiple shear device for controlled, staged actuation of downhole equipment or processes.

In accordance with a first aspect of the invention, there is provided a shear assembly for use downhole, the shear assembly comprising: a mandrel for integration within a work string; a shear sleeve slideable with respect to the mandrel to actuate a work string function; 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 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.

In accordance with a second aspect of the invention, there is provided a dual shear assembly for use downhole, the dual shear assembly comprising: a mandrel for integration within a work string; a first shear sleeve slideable with respect to the mandrel to actuate a first work string function; 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; a second shear sleeve slideable with respect to the mandrel to actuate a second work string function; 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 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. It will be apparent that a multiple shear assembly, that is one with three or more shearing sub-assemblies, is possible where n is the number of shearing functions and n-1 is the number of associated momentum-damping assemblies.

In an embodiment, 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.

In a suitable embodiment, the force of abutment is limited to a value less than the second threshold force.

In an embodiment, the dampening subassembly is a hydraulic dampening subassembly. The hydraulic dampening subassembly may comprise one or more annular pistons disposed within hydraulic chambers operatively attached to the mandrel. The chambers may be filled with hydraulic fluid of suitable viscosity to provide the desired degree of dampening for a specific application.

In an embodiment, the dampening subassembly reduces the abutment force by at least 10,000 pounds force.

In an embodiment, the second threshold force exceeds the first threshold force by more than 15%.