Optical measurements of oil release from calcite packed beds in microfluidic channels

To enable the study of improved oil recovery (IOR) from carbonate rock via laboratory experiments at the pore scale, we have developed a novel microfluidic chip containing a 3D packed bed of calcite particles. The utilization of fluorescently labeled water phase enabled visualization up to 1-2 particle layers with confocal laser scanning microscopy. Porosity and residual oil saturation (ROS) in this space are quantified from image stacks in the depth direction (Z). To obtain reliable average ROS values, Z stacks are captured at various XY locations and sampled over several time-steps in the steady state. All image stacks are binarized using Otsu's method, subsequent to automated corrections for imperfect illumination and Z-drifts of the microscope stage. Low salinity IOR was mimicked using a packed bed that was initially saturated with water and then with mineral oil. Steady state ROS values showed no significant dependence on capillary number (Ca) in the range from 6 x 10(-7) to 2 x 10(-5). In contrast, chemical modification of the pore space via adsorption of water-extracted crude oil components yielded significantly higher ROS values, in agreement with a more oil-wet porous medium. These results indicate a good potential for using packed beds on a chip as an efficient screening tool for the optimization and development of different IOR methods.