METHOD OF DRILLING A BOREHOLE INTO AN EARTH FORMATION

摘要

A method of drilling a borehole in an earth formation is provided, comprisin g the steps of: a) inserting a plurality of selected solid magnetisable particles into the borehole, the particles being susceptible of forming a filter cake layer at the borehole wall; b) drilling a section of the borehol e; and c) removing at least part of the filter-cake layer from the wall of said drilled borehole section by inducing a selected magnetic field in the borehole, withdrawing the particles from said wall.