This work describes an automated combinatorial process for selecting EOR surfactants. It is well known that low interfacial tension (IFT) required to mobilize oil corresponds to the appearance of middle phase microemulsions (Winsor III). Instead of systematic measurements of IFT, simple observation of phase behaviour in vials allows to select best formulations. As the number of parameters to be screened incorporate surfactants, co-surfactants, alkali and electrolytes, we have developed an automated method to accelerate the screening productivity. Among other requirements, critical issues we want to address concern compatibility with electrolyte, thermal stability and low cost.
Sample preparation is done in 48 well format using a robotic liquid handling platform that supports stirring and heating. In a first step, the brine concentration above which the surfactant is not soluble anymore is determined optically using a digital camera. In a second step, we take images of the phase behaviour of surfactant formulations in the presence of model oil (dodecane, vaseline). Image analysis is used to detect middle phase microemulsions. An estimate of interfacial tension can be derived from the volume of the middle phase microemulsion. Phase diagram observations can be recorded from room temperature up to 80°C. Results are in good agreements with classical methods used to measure low interfacial tension. An example study of phosphate esters will be discussed to illustrate the method.
This technique provides a powerful tool for testing formulations prior to more expensive core flood experiments.