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.

Ground reinforcement is a method used to reduce the damage caused by earthquakes. Usually, cement-based reinforcement methods are used because they are inexpensive and show excellent performance. Recently, however, reinforcement methods using eco-friendly materials have been proposed due to environmental issues. In this study, the cement reinforcement method and the biopolymer reinforcement method using sodium alginate were compared. The dynamic properties of the reinforced ground, including shear modulus and damping ratio, were measured through a resonant-column test. Also, the viscosity of sodium alginate solution, which is a non-Newtonian fluid, was also explored and found to increase with concentration. The maximum shear modulus and minimum damping ratio increased, and the linear range of the shear modulus curve decreased, when cement and sodium alginate solution were mixed. Addition of biopolymer showed similar reinforcing effect in a lesser amount of additive compared to the cement-reinforced ground, but the effect decreased above a certain viscosity because the biopolymer solution was not homogeneously distributed. This was examined through a shear-failure-mode test.

Geological CO₂ sequestration has been proposed as an effective solution to mitigate excessive human-emitted CO₂ in atmosphere. Knowledge of immiscible two-phase flow of CO₂-water/brine is necessary to evaluate the efficiency and safety of geological storage sites. Among forces dominating fluid flow, capillary pressure is highly important because of high uncertainty in measurement due to ambiguous wettability behavior of geomaterials. In particular, time-dependent wettability of geomaterials is of interest for predicting short-term performance of the storage site. After injection of CO₂ into an aquifer, both the CO₂ and water/brine in rocks pores are unsaturated and tend to dissolve into each other. Present study investigates the variation of contact angle on mica sheet using a captive bubble method at a wide range of pressures and salinities under unsaturated condition. Our results showed a general increase of contact angle with time. Comparison of unsaturated contact angle with previous results in the literature showed a wide span of wettability behavior, ranging from receding to advancing contact angle values reported in the literature. The observed decrease in wettability by time due to heterogeneity and pinning effect of triple line can jeopardize the safety of geological carbon sequestration projects in short-term after injection of CO₂.

The physical properties of granular materials (such as hydraulic, strength, and thermal properties) are largely dependent on their density (or porosity) and particle size distribution. In infrastructure design, the thermal properties of soils are now more important than in the past. However, our understanding of the thermal properties of mixed granular materials is still poor. In this study, the thermal conductivity of silica sands with different porosities and particle sizes was experimentally investigated, based on ASTM D5334-14. The thermal conductivity of granular materials is presented as a function of the porosity and proportion of fine particles. The thermal conductivity tends to be low when the porosity is high and the proportion of fine particles is low (and vice versa). When the fine particles are small enough to fill the pore body of the larger particles, the coordination number increases; thus, the thermal conductivity increases when the proportion of fine particles is high. Therefore, both the porosity and particle size distribution should be carefully considered when the thermal conductivity of mixed silica sand is evaluated.