An Improved Water-in-Oil Emulsion Mud

Abstract

Abstract A water-in-oil emulsion mud free of inert solids has been developed to provide a solution to certain problems associated with drilling, completing and servicing wells. Such invert-emulsion muds are satisfactory for use in wells with temperatures up to 300F and with pressures requiring densities up to 18 lb/gal. The emulsifier used in the preparation of these muds is the mixed salts of fatty acids. It is used in weighted muds in conjunction with a unique organophilic-clay suspending agent. The muds are prepared with ordinary mixing equipment at the wellsite. These muds have been used for drilling through the productive zone, for covering the zone to be perforated or to protect existing perforations during workover operations. Fewer difficulties in servicing wells and in getting wells back on production were experienced when these invert-emulsion muds were used as protective fluids to prevent water or mud from contacting exposed formations. Qualifications of Invert-Emulsion Muds An increasing number of wells are being drilled, completed and serviced with oil-base emulsion muds. These water-in-oil emulsions are commonly called "invert emulsions". The amount of water in an oil-base mud may vary from a trace to 60 per cent of the liquid volume of the mud. For purposes of this paper, the primary distinction between an invert-emulsion mud and an oil-base mud is based on whether the water is added as a definite part of the mud composition. In an invert-emulsion mud, the water phase has the important function of imparting controllable properties and characteristics to the mud. The muds described here have been found to have the most satisfactory properties when the water phase constitutes between 20 and 50 per cent of the liquid volume. In the experimentation and development of a general purpose invert-emulsion mud, certain requirements have gradually evolved. In the preparation of the mud:the emulsifier should be an easily handled, ground product, free of inert solids;the materials should be readily mixed with conventional rig mixing equipment in no longer time than required for mixing a water-base mud; andthe emulsifier should be effective for fresh and saline waters in a variety of crude and refined oils.