Minimum Miscibility Pressure (MMP) on a Chip

Minimum miscibility pressure determines whether gas injection will run in a miscible regime; an error in MMP leads to the wrong injection pressure, gas composition and development plan. A conventional slim-tube program needs a series of tests at different pressures, a large sample volume and considerable lab time, and the recovery curve alone says little about the miscibility mechanism.

Oil saturates a transparent microfluidic channel, then gas is injected at reservoir temperature over a series of pressures while the optical system records the transition from immiscible to miscible displacement. A homogeneous serpentine channel serves as a microfluidic slim-tube analog, and the test can be repeated on a porous micromodel with specified porosity and permeability to account for reservoir geometry.

Reservoir gas, CO₂, nitrogen, associated petroleum gas and prepared mixtures are compared under one protocol. Images are segmented, displacement metrics are plotted against pressure and the MMP is determined from interface disappearance, front morphology and residual oil saturation.

The test uses only a few milliliters of oil and gas. In a validation study, MMP was 33.2 MPa by the microfluidic test and 33.8 MPa by slim-tube at 110 °C — a difference of less than 5%. Microfluidic screening leaves only the most promising compositions and pressure ranges for conventional slim-tube confirmation.