Measurements of CO2-brine relative permeability in Berea sandstone using pressure taps and a long core

We measured CO2-brine relative permeability by performing five steady-state primary drainage experiments in a 116 mD Berea sandstone core at 20 degrees C and 10.34 MPa. We used a long (60.8 cm) core and four pressure taps to study and minimize end effects that can plague CO2-brine relative permeability measurements, and we obtained in situ saturation profiles using a medical X-ray Computed Tomography (CT) scanner. We found that entrance and exit effects propagated similar to 5 cm into the core, but the center sections of the core had uniform saturation. From the saturations and pressure drops, we obtained both CO2 and brine relative permeability in the center sections. We also obtained CO2 relative permeability at the entrance section where the brine saturation was lower and not uniform. The 15-cm long exit section of the core had non-uniform saturation and a measured pressure drop that was on the order of the capillary pressure and hence was unreliable for calculating relative permeability. We found that the CO2 and brine relative permeabilities determined in five experiments were consistent with each other and followed two simple Corey-type models that are similar to those seen in oil-brine relative permeability measurements. We discuss why end effects are much greater in the CO2-brine system than in oil-brine systems, and how this is a possible explanation of the low CO2 relative permeabilities recently reported for the CO2-brine systems. (C) 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.