Downhole casing expansion tool and method of expanding casings using the same

A downhole casing expansion tool comprising an expansion module for expanding a casing and a drive module for driving the expansion module to expand,

• wherein the drive module comprises a central tube, a core tube and an outer tube successively arranged from inside to outside of the drive module, in which a downstream end portion of the central tube can be closed and communicate with a drill shaft, and the central tube is provided with a liquid transfer aperture;
• the core tube which is fixedly connected to the drill shaft comprises a group of upstream and downstream core tube segments fixedly connected to one another via a first connecting member, wherein the downstream core tube segment is provided with a liquid inlet, and the core tube is slidably connected to the central tube via a limit member;
• and the outer tube which is connected to the core tube via a fourth shear pin comprises a group of upstream and downstream outer tube segments fixedly connected to one another via a second connecting member,
• wherein the first and second connecting members are arranged upstream and downstream of the liquid inlet respectively, and the first and second connecting members slidably contact with the outer tube and the core tube in a sealing manner respectively, so that the first connecting member, the second connecting member, the downstream core tube segment and the upstream outer tube segment together define a hydraulic chamber,
• wherein the expansion module comprises a plurality of expansion cone sheets movably mounted at a downstream end portion of the downstream outer tube segment and a cone seat fixedly arranged downstream of the expansion cone sheets,
• wherein in an initial state, the liquid transfer aperture does not communicate with the liquid inlet,
• and wherein as the casing expands, the central tube, with its downstream end portion being closed, moves downstream under the pressure of the liquid filled therein guided by the limit member, so that the liquid transfer aperture communicates with the liquid inlet, thus introducing the liquid into the hydraulic chamber to shear the fourth shear pin so as to drive the outer tube to move downstream, which in turn drives the expansion cone sheets to move downstream, wherein supported by the cone seat, the expansion cone sheets expand axially, so that the expansion of the casing is realized.