Effect of surfactant chemistry on drilling mud performance

Abstract

Drilling muds used in deepwater operations experience large variations in temperature, as well as pressure, when flowing through the different geometric conduits that are; the drill string, openhole (casing) - riser annuli present when drilling offshore. They behave as viscoelastic mixtures due to the suspension- and emulsion-dispersions used in their preparation. As a consequence, they display liquid-like and solid-like flow properties depending on the time scale of deformation they are subjected to. In addition to rate of deformation, environmental conditions such as temperature, and to a lesser extent pressure, are known to affect their rheological behavior.Nonionic surfactants are commonly used upstream in the stabilization of emulsions in drilling fluids, and in some instances as wetting agents. Inversion of pure emulsions systems stabilized by nonionic surfactants, from one type to another, as a result of temperature changes has been investigated and finds great application in the food and chemical industries.In this study, assessment of phase inversion occurrence in drilling muds, as well as resulting changes in their rheology was experimentally investigated at temperatures ranging from 0 to 90. Water- (WBM) and oil-based muds (OBM) samples were prepared using nonionic and ionic surfactants. Effect of surfactant nature and dispersed phase volume fraction on fluid loss properties of the different mud samples was equally carried at room temperature.Phase inversion of WBM samples stabilized by nonionic polyoxyethylene oleyl ether surfactants was observed for the range of conditions covered in the experimental investigation. Differences in flow behavior and apparent viscosity of the sample, as a result of inversion from one mud type to another, was equally noted.On one hand, the results underscored the importance of assessing potential application of nonionic surfactants to induce phase inversion in drilling fluids used for offshore operations. On the other hand, setbacks observed in the use of complex fluids for offshore drilling could possibly be accounted by the unknown occurrence of this phenomenon.