Pore-scale multiple-contact miscibility measurements in a microfluidic chip.

Carbon dioxide enhanced oil recovery is an interim solution as the world transitions to a cleaner energy future, extending oil production from existing fields whilst also sequestering carbon dioxide. To make this process efficient, the gas and oil need to develop miscibility over a period of time through the exchange of chemical components between the two phases, termed multiple-contact miscibility. Currently, measurements to infer the development of multiple-contact miscibility are limited to macroscopic visualization. We present a "rock-on-a-chip" measurement system that offers several potential measurements for different wetting conditions to infer the onset of multiple-contact miscibility. Here, a two-dimensional microfluidic porous medium with a stochastic distribution of pillars was created, and an analogue ternary system was used to mimic the real oil and gas multiple-contact miscibility process. Experiments were performed in two directions, imbibition and drainage, permitting study of different wetting properties of the host rock. The distinct behavior of trapped non-wetting ganglia during imbibition and the evolution of phase interfaces during drainage were observed and analyzed as the system developed miscibility. We show how these observations can be converted into rapid measurements for identifying the development of miscibility.