US Patent 10030474 Downhole sub with hydraulically actuable sleeve valve

A method for opening a port through the wall of a ported sub includes providing a sub with a port through its tubular side wall and providing a hydraulically actuable valve to cover the port. The valve can be actuable to move away from a position covering the port to thereby open the port. The method also includes increasing pressure within the sub to create a pressure differential across the valve to move the valve toward the low pressure side, while the port remains closed by the valve, and thereafter, reducing pressure within the sub to reduce the pressure differential to move valve away from a position covering the port.