Commonly called emulsion mud. Any conventional or special water-base drilling fluid to which oil has been added. The oil becomes the dispersed phase and may be emulsified into the drilling fluid either mechanically or chemically. (Bul D11)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}