Novel Nanofluidic Slim-Tube Approach for Visualizing Nanoscale CO2-oil Miscible Behavior and Measuring Minimum Miscible Pressure in Deep Reservoirs

Deep reservoirs with nanopores and ultra-low permeability remain underexploited due to low recovery rates and technical challenges. Miscible CO2 injection offers a promising solution to enhance recovery and reduce carbon emissions. However, accurately determining the minimum miscible pressure (MMP) in these reservoirs is challenging, as traditional slim-tube tests cannot replicate nanopore behavior or provide direct visualization. In this study, we introduced a novel nanofluidic slim-tube method for measuring nanoscale MMP and visualizing CO2-oil displacement in 100 nm nanopores. This method closely mimics deep reservoir conditions and overcomes the limitations of conventional methods, which rely on larger pores. The nanofluidic approach significantly reduces sample volume (~0.59 μL) and testing time (from six weeks to six hours), enabling rapid, high-throughput, and reliable MMP measurements. We observed both immiscible and miscible CO2 displacement processes in nanopores. CO2 immiscible displacement occurs in two stages: dissolution contributes 8.41% and immiscible displacement contributes 89.92% to the total displacement. In contrast, CO2 miscible displacement also proceeds in two stages, with dissolution contributing 19.09% and the miscible stage contributing 80.91% to the total recovery. The nanofluidic slim-tube method offers significant advantages in measurement accuracy, testing efficiency, and visualization, making it a promising tool for enhanced oil recovery, CO2 sequestration, and fluid displacement studies in deep reservoirs.