Abstract: The invention relates to the field of drilling wells into a subterranean formation for the purpose of extracting or producing minerals contained by said formation. The invention specifically relates to drilling fluids used in such methods to form filter cakes for providing a sealing layer on the walls of boreholes formed by the drilling. A new bridging agent for use in such drilling fluids has been found, which has the great advantage that a good sealing filter cake is produced, which filter cake can be removed under very mild conditions.