Low-permeability reservoir sample wettability characterization at multiple scales: Pore-, micro- and macro-contact angles

Abstract

Wettability, characterized by contact angle (θ), determines fluid distribution/migration in low-permeability (‘unconventional’) hydrocarbon reservoirs. However, θ is a scale-dependent parameter, i.e., pore- (θpore), micro- (θmicro) and macro- (θmacro) contact angles can vary substantially. Therefore, herein, θpore was estimated using a new theoretical model applied to nanoliter droplet imbibition dynamics. θmicro was measured inside an environmental scanning electron microscope through sessile nanoliter droplets; θmacro was quantified at ambient conditions through sessile microliter droplets. The effect of nanoliter droplet size on low-permeability rock wettability was also studied. Results demonstrate that: 1) θpore >θmicro >θmacro; 2) θmicro reflects local wettability heterogeneity better than θmacro; 3) a larger droplet size causes a greater θmicro for weakly water-wet low-permeability rocks, while there is no clear relationship between droplet size and θmicro for strongly water-wet low-permeability rocks. Studies of this nature can be used to evaluate the controls on multi-phase flow in unconventional hydrocarbon reservoirs as applied to hydrocarbon extraction or greenhouse gas sequestration.