Global energy demand continues to drive oil and gas exploration in increasingly challenging environments. The extreme temperatures and pressures drilling fluids are subjected to require optimum design of their rheology. Among the numerous components used in the design of drilling fluids are surfactants. Surfactants play an important role in the emulsification of immiscible liquids as well as the alteration of cuttings wettability to facilitate transport to the surface.

Nonionic surfactants, depending on their chemical group allow the inversion of oil-in-water emulsions (O/W) to water-in-oil (W/O) and vice-versa depending on the direction of temperature change. In this study, emulsion-suspension samples were prepared with different nonionic surfactants at Oil:Water ratios of 50:50 and 60:40. The mechanical properties of the samples was assessed using a scientific rheometer at temperatures ranging from 0–90 °C.

Phase inversion from oil-in-water to water-in-oil was observed for samples stabilized by polyoxyethylene oleyl ether surfactants. Build up in the apparent viscosity of the samples was observed following phase inversion, mainly resulting from the formation of nanosized dispersed water droplets.

Findings in the study highlighted the possibility of obtaining different drilling fluid types during downhole circulation, thereby paving a path for the design optimization of drilling fluids used in offshore operations.

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