pumped down the casing string under high pressure to remove the obstruction the sealing packer 107 facilitates this operation by inhibiting liquid under high pressure escaping through the top of the casing 30 referring to fig4 and 5 there is shown an apparatus in accordance with a third embodiment of the present invention which is generally identified by the reference numeral 201 the apparatus comprises a cylindrical body 202 with a threaded connection 203 at the upper end for connection to a top drive attached to the cylindrical body 202 or machined into it is a hydraulic cylinder 204 with threaded ports 205 206 at opposite ends these ports 205 and 206 permit hydraulic fluid to be injected under pressure to manipulate a hydraulic piston 207 secured within the cylinder by a threaded lock ring 208 a compression spring 209 is located in the cylinder 204 above the piston 207 a grapple 210 provided with serrated teeth machined into its outer surface is provided around the cylindrical body 202 below the hydraulic cylinder 204 the grapple 210 is connected to the hydraulic piston 207 by a threaded connection 211 a corresponding wedge lock 212 is provided on the cylindrical body 202 the grapple 210 and corresponding wedge lock 212 are located in use inside a casing 213 the piston 207 and lock ring 208 are fitted with seal rings not shown to prevent hydraulic fluid leakage a mud check valve 214 is connected by a threaded connection at the lower end of the wedge lock 212 below this valve is.