Method of cleaning a well bore prior to a cementing operation

Abstract

Once the drilling of an oil or gas well is finished the bore must be cased and cemented. It is important that the cement lining be complete, and to ensure this it is necessary to sweep out the mud in the annulus ahead of the rising cement. Unfortunately, this often proves difficult, and various procedures and mechanisms have been devised in the past to improve the chances of achieving efficient mud-removal and forming a complete cement lining, though none have been truly successful. One of the techniques presently employed involves the utilization of a wash, but it has been noted that such a wash, even when turbulent, has very little component of its movement in the annulus in a direction other than up along the annulus, and that as a result it has very little effect on gelled mud deposits, especially those in the small casing/bore inter-distance of a severely eccentric casing. It has now been discovered that a considerably increased amount of lateral motion, and thus a very significantly enhanced degree of mud removal capability, is provided if the liquid be a multiphase liquid in which one of the phases is a gas--in other words, if the liquid be full of bubbles--and the invention provides a cleaning method particularly suitable for the cleaning of gelled mud deposits off the casing and bore walls of an oil/gas well prior to cementing the casing in place, in which there is caused to flow over and in contact with the dirty surface a 'burbulent' liquid.