Downhole tool and method

摘要

A cleaning tool (1) for use in cleaning ferrous material from a wellbore has a magnetic cleaning functionality by provision of magnets (5) in an Halbach array on a downhole tool component of a workstring. The Halbach array may be an Halbach cylinder positioned on a mandrel wherein the magnetic field is external to the cylinder with substantially zero magnetic field within the tool.

主权项

1. A downhole debris recovery tool comprising:
an elongate body having an axial throughbore and pin and box end configurations for assembly of the tool into a workstring, the elongate body further having a recessed surface for receipt of magnetic elements, and a pair of semi-cylindrical parts each having an array of uniformly sized magnetic elements configured to form an Halbach array when the semi cylindrical parts are formed together into a cylinder, wherein the semi-cylindrical parts are arranged in the recessed surface of the elongate body to form the Halbach array of cylindrical form, and a close-fitting cylindrical sleeve slidable over the cylinder having the Halbach array, the close-fitting cylindrical sleeve secured to the elongate body by provision of stabilizers which overlay respective ends of the sleeve with sufficient clearance in respective recesses so that the sleeve is restrained with respect to axial displacement between the stabilizers and freely rotatable with respect to the stabilizers.