Microfluidic determination of minimum miscibility pressure (MMP) in dynamic CO₂/n-decane flow

Carbon dioxide enhanced oil recovery (CO₂-EOR) has been recognized as a viable pathway for carbon capture, utilization, and storage (CCUS). Among its variants, miscible CO₂-EOR offers a considerable additional oil recovery of approximately 5-20%, making the determination of minimum miscibility pressure (MMP) a critical design consideration. In this study, we employ a high-pressure microfluidic platform to investigate the miscibility transition between CO₂ and n-decane at temperatures (T) of 40, 50, 70, and 90 °C. At T = 40 °C, with increasing pressure (P), microfluidic visualization reveals a series of distinct flow regimes: dripping, quasi-steady jetting, unsteady jetting, transitional, and ultimately diffusive regimes. In the diffusive regime, miscibility is achieved through intensive mixing, leading to the disappearance of the fluid-fluid interface. Based on these microfluidic observations, we propose a new criterion for MMP determination: the minimum pressure required to reach the diffusive regime for the dynamic CO₂-oil flow. The experimentally determined MMP values show good agreement with previous microfluidic studies and predictions from the Peng-Robinson equation of state (PR-EOS). Furthermore, the MMP increases linearly with temperature from 40 to 90 °C, consistent with the reduced solubility of CO₂ in n-decane at higher temperatures. This microfluidic method provides a rapid and visual approach to assess miscibility transitions in CO₂-EOR applications.