Downhole cleaning tool

Abstract

A downhole borehole cleaning apparatus () for recirculating drill cuttings contained in a downhole borehole is provided and has a body () having an outer surface for contacting downhole fluid containing said drill cuttings, the downhole fluid comprising a certain pressure within the downhole borehole (). The body () has a pair of bearing surfaces (U;D) spaced apart along the longitudinal axis of the body (), and the pair of bearing surfaces (U;D) comprise substantially the same maximum outer diameter (d) which is greater than the maximum outer diameter of the rest () of the body (). Each of the pair of bearing surfaces (U;D) comprises a substantially constant and un-interrupted diameter (d) around its whole outer circumference for at least a portion of its longitudinal length; this forces all of the drilling fluid to pass around that maximum outer diameter. The outer surface of the body () further comprises a low pressure generation means () located in between the two longitudinally spaced apart bearing surfaces (U;D) for generating a region of lower pressure in the downhole fluid within that region compared to the said certain pressure. A method of cleaning a downhole borehole is also described involving miming in a work string comprising a downhole borehole cleaning tool () into a borehole to be cleaned, and permitting or arranging for relative movement to occur between the downhole borehole cleaning tool () and fluid located in the annulus () in the borehole () whereby drill cuttings are recirculated.