Characterizing Static and Dynamic Capillary Pressure in Porous Media Using a Novel Microfluidic Pressure Sensor

Capillary pressure is a critical parameter in multiphase flows in porous media. Traditional models often describe these flows based on empirical constitutive relations of capillary pressure which however exhibit strong hysteresis. It has been the goal for many recent studies to develop a nonhysteretic relation of capillary pressure to link the pore scale processes with the macro-scale observations. However, direct measurement at the pore level is hindered by the small scale and the stringent requirements for spatial and temporal resolutions. To that end, we developed an on-chip pressure sensor using soft lithography with a thin polydimethylsiloxane (PDMS) membrane. This membrane deflects in response to pressure changes, which are quantified optically using astigmatic particle tracking. Integrated with a high-speed camera and microscope, our setup enables real-time, in-situ measurement of capillary pressure within individual pore spaces, offering unprecedented insights into pore-scale mechanisms. Furthermore, we optimized the response time of the sensor to enable instantaneous measurement of dynamic pressure at the pore level. These quantification will be compared with conventional measurement such as bulk flow pressure transducers and image-based calculations, providing new insight into the hysteretic behavior of capillary pressure as well as validations of new functional forms.