Method of drilling a borehole into an earth formation

摘要

A method of drilling a borehole in an earth formation is provided, the borehole containing a body of drilling fluid. The method includes 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 and being made of a material susceptible of being exposed to magnetic forces when subjected to a magnetic field; b) drilling a section of the borehole; and, c) removing at least part of the filter-cake layer from the wall of the drilled borehole section by inducing a selected magnetic field in the borehole, the magnetic exerting magnetic forces to the particles withdrawing the particles from the wall.