Direct Measurement of Minimum Miscibility Pressure of Decane and CO₂ in Nanoconfined Channels

Determining gas and oil minimum miscibility pressure (MMP) plays a vital role in the enhanced oil recovery. Injecting gases above the MMP into oil reservoirs leads to a relatively high oil recovery ratio. For conventional reservoirs, the fluid bulk MMP is measured by lab techniques such as the rising bubble approach. However, for the increasingly important tight and shale reservoirs, oil is confined in nanoscale pores. Nanoscopic MMP remains largely unknown from experiments and relies heavily on theoretical predictions. To close this gap, we developed a nanofluidic device to determine the MMP down to 50 nm by measuring the fluorescence intensity change in a nanoconfined channel. CO₂ and decane are used as the working fluids, with 1% fluorescent dye for characterization. At the isothermal condition, the fluorescence intensity in decane reduces with the injecting CO₂ pressure increasing, and the maximum fluorescence intensity reduction at certain CO₂ pressure indicates the MMP being reached. We measured and compared CO₂ and decane MMP at the bulk scale (5 μm) and nanoscale (50 nm). The experimental results align well with literature data and theoretical predictions. Importantly, our nanofluidic approach provides a promising strategy to determine the nanoscopic fluid MMP and is readily applicable in assisting the enhanced tight/shale oil recovery.