Special non polluting emulsifier for non aqueous drilling fluids in deep offshore drilling

With the increasing number of deep offshore drilling operations and severe environmental constraints, operators and service companies are confronted to more and more complex technical challenges. Extreme conditions encountered at these water depths require an adaptation of the drilling mud composition and properties. In particular, range of temperature and pressure (close to 0 °C and up to 400 bar) are favorable conditions to the formation of gas hydrate solid structures that are liable to plug kill and choke lines as well as the annular, and may also cause interruption of the drilling operations and even destruction of the rig equipment. Oil based muds generally formulated as invert emulsions are difficult to stabilize over a large range of pressure and temperature conditions and specially at low temperature and high pressure where the appearance of hydrate compounds may induce a destabilization of the emulsion and loss of well control (cuttings transport, mud losses ....). This paper presents credible laboratory data demonstrating the benefits of a special non polluting surfactant system engineered to stabilize brine droplets in an oil phase and to act as an efficient barrier to avoid droplets coalescence, even during hydrate formation. By using Differential Scanning Calorimetry technique without any dilution of the fluid, we show that emulsion droplet size is unaffected by ageing over a large range of temperatures; an adequate choice of oil plus the surfactant system permits to limit the amount of hydrate formed. Furthermore, the use of this specific emulsifying system allows to avoid agglomeration of droplets in the fluid as well as the breakage of emulsions after hydrate dissociation.