Abstract
The pore-level two-phase fluids flow mechanism needs to be understood for geological CO2 sequestration as a solution to mitigate anthropogenic emission of carbon dioxide. Capillary pressure at the interface of water–CO2 influences CO2 injectability, capacity, and safety of the storage system. Wettability usually measured by contact angle is always a major uncertainty source among important parameters affecting capillary pressure. The contact angle is mostly determined on a flat surface as a representative of the rock surface. However, a simple and precise method for determining in situ contact angle at pore-scale is needed to simulate fluids flow in porous media. Recent progresses in X-ray tomography technique has provided a robust way to measure in situ contact angle of rocks. However, slow imaging and complicated image processing make it impossible to measure dynamic contact angle. In the present paper, a series of static and dynamic contact angles as well as contact angles on flat surface were measured inside a micromodel with random pattern of channels under high pressure condition. Our results showed a wide range of pore-scale contact angles, implying complexity of the pore-scale contact angle even in a highly smooth and chemically homogenous glass micromodel. Receding contact angle (RCA) showed more reproducibility compared to advancing contact angle (ACA) and static contact angle (SCA) for repeating tests and during both drainage and imbibition. With decreasing pore size, RCA was increased. The hysteresis of the dynamic contact angle (ACA–RCA) was higher at pressure of one megapascal in comparison with that at eight megapascals. The CO2 bubble had higher mobility at higher depths due to lower hysteresis which is unfavorable. CO2 bubbles resting on the flat surface of the micromodel channel showed a wide range of contact angles. They were much higher than reported contact angle values observed with sessile drop or captive bubble tests on a flat plate of glass in previous reports. This implies that more precaution is required when estimating capillary pressure and leakage risk.
Highlights
Despite all the efforts towards developing renewable energy, fossil fuels are still the main source of energy
Geological CO2 sequestration has been recently developed as a promising method to decrease anthropogenic CO2 emission
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Summary
Despite all the efforts towards developing renewable energy, fossil fuels are still the main source of energy. The main idea of this method is to separate CO2 (i.e., CO2 from other gases in main emitters such as fossil fuel-based power plants and other industrial units), transfer it by pipelines or tanks, and inject it into underground layers such as depleted oil and gas reservoirs, deep saline aquifers, deep unmineable coal beds, and methane hydrate bearing sediments. This injected CO2 is trapped underground by two short-term mechanisms: structural trapping and capillary (or residual) trapping. They can trigger the safer long-term mechanisms
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