In-line Partition Coefficient Measurement for Oil Field Tracers Utilizing Microfluidic Mixing Chip
Authors: Chang Sehoon , Thomas Gawain , Wang Wei 
Published: March 2023

Abstract
Oil field tracers are extensively utilized to evaluate and understand production data, pressure test analysis, inter-well connectivity, as well as enhanced oil recovery (EOR). One of the important properties of the tracer is the partition coefficient, which is the ratio of tracer concentrations in the oil and water phases at equilibrium state. Therefore, partitioning coefficient measurement is necessary for both partitioning and non-partitioning tracer development. However, the current technology for the measurement requires large quantities of organic solvent and long measurement time. Here, we developed the fast, portable, low-solvent and sustainable device so called in-line partition coefficient measurement system for oil field tracers utilizing a microfluidic chip and oil/water separator.
To minimize the amount of sample, solvent, measurement time and cost, microfluidic technology has been used for the miniaturization of the partition coefficient measurement. Utilizing microfluidic chip and oil/water separator decreased the characteristic length of diffusion and therefore time required to complete the experiment. The in-line optical property measurement such as UV-Vis, fluorescence, or time-resolved fluorescence has been used for the tracer in water solution at various concentrations for the reference curves. The tracer in water solution was injected into the teardrop microfluidic mixing chip using syringe pump and the crude oil was injected concurrently using a separate syringe pump. Fluid samples were thoroughly mixed in microfluidic mixing chip then the solution flows into a membrane-based oil/water phase separator system (Zaiput, inc). After separation, only the water phase flows into in-line HPLC UV-Vis or fluorescence, time-resolved fluorescence detector.
The measurement results of both partitioning and non- partitioning tracers showed similar to the calculated value of the partitioning coefficient and the value from the literature that used the conventional shake-flask method. Especially, the in-line partition coefficient measurement takes only tens of minutes, which is much faster than the conventional shake-flask method (couple of days). Also, the developed measurement is cost-effective saving a large amount of expensive organic solvent utilized for the conventional measurement. The developed in-line microfluidic mixing chip aided partitioning coefficient measurement process facilitates measurement of essential properties of oil field chemicals because we can estimate the value simply by switching from the flow of water itself to the flow of mixture solution.
The developed method demonstrates an improvement on conventional partitioning coefficient measurements for a variety of oil field tracers in terms of sustainability. The microfluidic in-line partition coefficient measurement not only minimizes cost and human intervention, but also provides enhanced sample analysis throughput. This technology is ready to be validated for the wide variety of oil field chemicals utilized for EOR processes as well as oil field tracers.