Pore-Scale Investigation of Dynamic Immiscible Displacement in Layered Media using Synchrotron X-ray Microtomography.

Understanding the dynamics of immiscible fluid in a porous media is critical in many chemical and environmental engineering processes. However, the geological heterogeneity effect on multiphase flow behavior remains unclear. Here, the dynamics of immiscible fluid displacement and entrapment were experimentally demonstrated at pore-level using time-lapse synchrotron X-ray microtomography. A drainage-imbibition experiment was designed using an unconsolidated layered sand pack that comprised coarse sand and fine sand zones. There were significant differences between the two zones, with regard to the temporal variations in fluid saturation and morphological evolution of nonwetting fluid (oil) during imbibition. Highly connected oil clusters in the coarse zone broke up into many small fragments, whereas the cluster in the fine zone remained connected while spanning multiple pores. To further understand the impacts of pore size and connectivity on multiphase fluid dynamics, a new approach that tracks the temporal variation of immiscible fluid in individual pores was conducted. The surface area at the oil-water interface increased during imbibition, which is expected to facilitate mass transfer and surface interactions. Understanding immiscible fluid displacement in layered porous media at the pore-level could lead to more effective environmental remediation.

Evaluation of optimal size of illite adsorbent for 137Cs removal in contaminated artificial lake.

Since the Chernobyl and the Fukushima Daiichi disasters, contamination caused by radioactive accidents has attracted increasing attention. The present study evaluated immediate cleanup of 137Cs dissolved in surface water reservoir using an illite adsorbent, simulating an event of 137Cs contamination at Lake Paldang, South Korea. The study was conducted in two parts: (1) calculation of the residence time (tr) of illite adsorbent, and (2) evaluation of the adsorption time (ta) of illite adsorbent. tr was calculated based on physical properties (e.g., density, diameter, shape, and roughness) of the illite adsorbent at designated depth of surface water. Subsequently, ta was measured for 4 illite adsorbents (Korea01-Illite, Korea02-Illite, USA-Illite, and China-Illite) at 100 and 100,000 µg/L Cs, via kinetic adsorption experiment. Upon spraying of illite adsorbents with 50-150 µm diameter to locations where lake depth was between 6.5 m and 25.5 m, tr ranged from 0.132 to 3.300 h ta of 4 illite adsorbents was shorter than 0.6 and 2.5 h, for respective tests using 100 and 100,000 µg/L Cs. Based on the two characteristic times (tr and ta), the optimal particle diameter for the 4 illite adsorbents were evaluated at available lake depths in Lake Paldang. The study revealed that the USA-Illite is the efficient adsorbent at 100 µg/L Cs; in contrast, China-Illite could serve as the effective adsorbent at 100,000 µg/L Cs. Also, it was suggested that adsorbent efficiency had seasonal variations; tr was 2 h longer in winter than summer. In general, the study suggests that in the event of 137Cs contamination at Lake Paldang, Korea01-Illite is likely the best adsorbent to remove 137Cs due to its removal efficiency and accessibility from the illite deposit in Korea.

Evaluation of multiple PRPs' contributions to soil contamination in reclaimed sites around an abandoned smelter.

Although soil contamination must be remediated by the polluters under current legal frameworks in numerous countries, the allocation of responsibilities for soil clean-up is still challenging in the case of multiple potentially responsible parties (PRPs). This study evaluated the individual contributions of two PRPs (Owners A & B) to heavy metal contamination in the soil environment near an abandoned smelter and compared the results with those from the conventional Gore Factor (GF) method. The soil in the study area was widely contaminated by various heavy metals. In particular, the arsenic concentration exceeded the local regulatory level of 25 mg kg-1 at all investigated sites. Arsenic components were frequently observed in the form of iron oxides, and they decreased with increasing distance from the smelter chimney. This distribution supported the premise that the arsenic mainly originated from the chimney through oxidation processes of iron-containing ores under high temperature. The GF results attributed greater responsibility to Owner A than Owner B, while the estimated arsenic masses (based on the field investigation) indicated the contrary. These results could be caused by insufficient information for the GF evaluation, because the change in smelter ownership and long history of contamination obscure important data, such as the amount of total refined ores and the efficiency of air pollution prevention facilities in the smelter. Therefore, more field-based approaches must be considered more importantly for the evaluation of multiple PRPs' remediation responsibilities, especially in areas with long-term contamination.

Two-phase flow visualization under reservoir conditions for highly heterogeneous conglomerate rock: A core-scale study for geologic carbon storage.

Geologic storage of carbon dioxide (CO2) is considered a viable strategy for significantly reducing anthropogenic CO2 emissions into the atmosphere; however, understanding the flow mechanisms in various geological formations is essential for safe storage using this technique. This study presents, for the first time, a two-phase (CO2 and brine) flow visualization under reservoir conditions (10 MPa, 50 °C) for a highly heterogeneous conglomerate core obtained from a real CO2 storage site. Rock heterogeneity and the porosity variation characteristics were evaluated using X-ray computed tomography (CT). Multiphase flow tests with an in-situ imaging technology revealed three distinct CO2 saturation distributions (from homogeneous to non-uniform) dependent on compositional complexity. Dense discontinuity networks within clasts provided well-connected pathways for CO2 flow, potentially helping to reduce overpressure. Two flow tests, one under capillary-dominated conditions and the other in a transition regime between the capillary and viscous limits, indicated that greater injection rates (potential causes of reservoir overpressure) could be significantly reduced without substantially altering the total stored CO2 mass. Finally, the capillary storage capacity of the reservoir was calculated. Capacity ranged between 0.5 and 4.5%, depending on the initial CO2 saturation.

A predictive estimation method for carbon dioxide transport by data-driven modeling with a physically-based data model.

In this study, a data-driven method for predicting CO2 leaks and associated concentrations from geological CO2 sequestration is developed. Several candidate models are compared based on their reproducibility and predictive capability for CO2 concentration measurements from the Environment Impact Evaluation Test (EIT) site in Korea. Based on the data mining results, a one-dimensional solution of the advective-dispersive equation for steady flow (i.e., Ogata-Banks solution) is found to be most representative for the test data, and this model is adopted as the data model for the developed method. In the validation step, the method is applied to estimate future CO2 concentrations with the reference estimation by the Ogata-Banks solution, where a part of earlier data is used as the training dataset. From the analysis, it is found that the ensemble mean of multiple estimations based on the developed method shows high prediction accuracy relative to the reference estimation. In addition, the majority of the data to be predicted are included in the proposed quantile interval, which suggests adequate representation of the uncertainty by the developed method. Therefore, the incorporation of a reasonable physically-based data model enhances the prediction capability of the data-driven model. The proposed method is not confined to estimations of CO2 concentration and may be applied to various real-time monitoring data from subsurface sites to develop automated control, management or decision-making systems.

Comparison of physicochemical properties between fine (PM2.5) and coarse airborne particles at cold season in Korea.

Although it has been well-known that atmospheric aerosols affect negatively the local air quality, human health, and climate changes, the chemical and physical properties of atmospheric aerosols are not fully understood yet. This study experimentally measured the physiochemical characteristics of fine and coarse aerosol particles at the suburban area to evaluate relative contribution to environmental pollution in consecutive seasons of autumn and winter, 2014-2015, using XRD, SEM-EDX, XNI, ICP-MS, and TOF-SIMS. For these experimental works, the fine and coarse aerosols were collected by the high volume air sampler for 7 days each season. The fine particles contain approximately 10 µg m(-3) of carbonaceous aerosols consisting of 90% organic and 10% elemental carbon. The spherical-shape carbonaceous particles were observed for the coarse samples as well. Interestingly, the coarse particles in winter showed the increased frequency of carbon-rich particles with high contents of heavy metals. These results suggest that, for the cold season, the coarse particles could contribute relatively more to the conveyance of toxic contaminants compared to the fine particles in the study area. However, the fine particles showed acidic properties so that their deposition to surface may cause facilitate the increase of mobility for toxic heavy metals in soil and groundwater environments. The fine and coarse particulate matters, therefore, should be monitored separately with temporal variation to evaluate the impact of atmospheric aerosols to environmental pollution and human health.

Transport of groundwater, heat, and radiogenic He in topography-driven basins.

The goal of the study is to assess the feasibility of characterizing the caprock integrity by utilizing sampled helium (He) concentration in fluids and temperature measurement prior to CO2 injection. A series of simulations representing pre-CO2 injection phase was conducted to reveal the spatial distribution of groundwater, temperature, and He concentration under various geologic conditions of topographically driven basin. Then, their profiles in preinjection conditions were compared with dynamic signatures of both injection-induced pressure and leaked brine concentration at post-CO2 injection conditions. In the topographic basin, He and heat transports generally show analogous transport except the low-permeability basin where the conductive heat and diffusive solute transports are the primary transport mechanisms. The transition occurred at permeabilities between 10(-15) and 10(-14) m2. Inclusion of low-k layer (low-k layer: 10(-16) m2 and surrounding basin: 10(-13) m2) segregates shallow and deep groundwater system and creates a 3-km single large free convection of groundwater driven by unevenly distributed thermal profile of basin. Finally, He and temperature profiles with high-k pathways at pre-CO2 injection scenarios and NaCl mass fractions at post-CO2 injection showed systematic trends and relationships, suggesting that proper understanding of these trends will aid to identify the seal integrity.