Abstract: The invention relates to washpipe assemblies for use in well bores and provides a washpipe assembly (2) comprising a washover shoe (10) attached to a washpipe (18), wherein a washpipe stabiliser (22) is provided on the washpipe (18) so that, when in use, deflection of the washover shoe (10) from a desired position is substantially prevented. The washpipe assembly of the present invention has the advantage over the prior art assemblies of providing means for supporting the washpipe off the wall of a well bore or well bore casing (52), and thereby reducing the torque required to rotate the washover string and the tendency of the washover shoe (10) to deviate from its preferred path down the well bore.

Abstract: A method of forming and lining a branch borehole includes installing a packer in a main borehole, installing a whipstock on the packer, milling a window in the main borehole casing using the whipstock, recovering the whipstock, and then installing a deflector (20) to deflect a lining into the lateral. The external diameter (D) of the deflector is less than the internal diameter of the casing of the main borehole so as to permit subsequent milling away of cement and surplus lining material using a washover tool or thin-walled mill. The preferred deflector includes a relatively steep deflector face (21) at the upper end of the deflector and a relatively shallow deflector face (22) which connects the lower end (23) of the face (21) to the full diameter (D) of the deflector. If it is desired to use the maximum possible diameter casing for the lateral, portions of the formation and/or the main borehole casing are removed by an appropriate tool after the deflector (20) has been positioned within the borehole.

Abstract: Apparatus for milling the casing of an oil or gas well comprises a downhole assembly which is run into the well on a rotatable drill string. The assembly comprises a motor (6) the body of which is connected to the drill string and the output shaft of which is connected to a casing mill (9). In use, the drill string is rotated in one rotational direction and the motor (6) is operated to rotate the output shaft thereof in the same rotational direction whereby the speed of rotation of the mill (9) is faster than the rotational speed of the drill string. Because the rotational speed of the milling tool (9) cannot be less than the rotational speed of the output shaft of the motor (6) relative to the body thereof extreme variations in the rotational speed of the milling tool due to winding up of the drill string are avoided. The downhole assembly may incorporate a taper mill (11), stabilizers (10, 8 and 5) and a jet sub (4).