Patent ID: 7665545

Claim:
A method for providing a temporary controlled increase in fluid pressure at a selected location in a work string to operate a tool in a well bore, the method comprising the steps; (a) mounting a pressure shear sub in the work string below the tool, the shear sub comprising a tubular body and at least one valve member moveable relative to the tubular body, and the shear sub having a first configuration with the at least one valve member in a first position to provide fluid flow through a central bore of the work string; a second configuration with the at least one valve member in said first position, wherein introduction of a ball to the at least one valve member provides for blocking fluid flow through the bore and; a third configuration with the at least one valve member in a second position, returning fluid flow through the sub via a bypass channel, the shear sub being operable from the second to the third configuration by a predetermined fluid pressure; (b) running the work string into a well bore and flowing fluid through a bore at a first pressure, below the predetermined pressure; (c) locating the pressure shear sub below the selected location in the well bore; (d) dropping the ball into the bore to locate in the shear sub and cause the shear sub to operate in the second configuration in said first position; (e) building up fluid pressure in the bore towards an intermediate pressure that is sufficient to operate the tool and is less than the predetermined fluid pressure; (f) operating the tool by using the intermediate fluid pressure at the selected location; and (g) continuing to build up pressure in the bore to the predetermined fluid pressure and causing said at least one valve member to move relative to the tubular body from the first position to the second position to configure the shear sub in the third configuration and re-establish fluid flow through the work string.