Patent ID: 7690432

Claim:
A method of drilling a wellbore, comprising: running a drill string into the wellbore and a bore of a casing string, the casing string comprising: a first hydraulic port, a valve member moveable between an open position and a closed position, wherein the valve member substantially seals a first portion of the casing bore from a second portion of the casing bore in the closed position, a valve actuator operable to open the valve member in response to receiving hydraulic fluid from the first hydraulic port, and a hydraulic actuator comprising a hydraulic fluid reservoir and in fluid communication with the casing bore and an annulus defined between the casing and the wellbore and operable to inject hydraulic fluid into the first hydraulic port in response to annulus pressure exceeding casing bore pressure; increasing the annulus pressure so that the annulus pressure is greater than the casing bore pressure, thereby opening the valve member; and drilling the wellbore using the drill string.