RESUMO
Carbon dioxide enhanced oil recovery (CO2-EOR) has been widely used to improve production from mature oil fields around the world. To be effective, the injected gas and reservoir oil must develop miscibility, which generally requires prolonged contact between the two phases while in relative motion. Thus, identifying whether miscibility is possible is crucial for determining the feasibility of such EOR projects. The current industry-standard method of characterization, the slim-tube, requires weeks of analysis, while alternative methods are unable to infer all routes to miscibility, producing significant overestimates in required pressures. Microfluidic devices have the potential to simplify and speed up the analysis by offering high levels of fluid control and excellent visualization. Recently, high-pressure microfluidic devices etched into glass and exploiting crude oil's natural fluorescence have been successfully demonstrated. Here we focus on designing a microfluidic channel for identifying the development of miscibility. We prove its accuracy for a known ternary fluid system that mimics the true oil-gas system and can be manipulated at room temperature and pressure. Our chip consists of a single channel with several inline pocket structures. The chip is initially flooded with one phase before a second phase is injected via a flow-rate-controlled pump. The first phase is then rapidly displaced in the primary channel, but small samples are retained within the pockets. Over time, these trapped droplets can be observed as they interact with the continuously flowing second phase. When the fluid concentrations meet the conditions for development of miscibility, a dramatic and visually observable change in behavior occurs, allowing for characterization within 2 h.
RESUMO
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.