Measurements of dynamic contact angles in solid–liquid–liquid systems at elevated pressures and temperatures

This paper presents a recently developed technique, which has been used successfully in several oil-field applications, to generate reproducible measurements of both the water-advancing and -receding contact angles at reservoir conditions of temperature and pressure using live reservoir fluids. Unlike the conventional sessile drop and modified sessile drop contact angle tests, which require 30–40 days to complete, the new technique enables these measurements within 2–3 days while assuring measurement accuracy within about 2–3°. The new technique is called the dual-drop–dual-crystal (DDDC) technique, and involves the equilibration of two parallel solid surfaces immersed in reservoir brine with two crude oil drops placed on them before creating the advancing and receding interfaces. The fluids–solid equilibrium is attained quickly due to the effect of buoyancy forces that help in draining the water film trapped between the crude oil drop and the solid surface. Dynamic measurements are presented to demonstrate the dynamic behavior of the oil–water–rock three-phase boundary in water-, intermediate- and oil-wet solid–fluid systems. The paper includes the methodology and salient features of the new technique, some of the recent results to demonstrate its accuracy and short run times, and actual reservoir cases involving serious wettability shifts caused by fluids incompatibility and temperature variations. Due to its accuracy, short run duration and operability at reservoir conditions, the new technique offers excellent potential for detailed understanding of the influence of various surfactants used in oil-field operations on reservoir wettability alteration, screening and optimization of fluids for field applications, optimization of production strategies, and for many other practical applications involving solid–liquid–fluid systems.