No abstract

As one of the solutions to tackle climate change caused by excess carbon dioxide (CO2) emission, CO2 geological storage has been increasingly implemented globally to store CO2 securely and permanently in the subsurface. In the current study, structural trapping, which shows the potential of initial CO2 containment and integrity of the subsurface structure, is experimentally investigated with CO2 leakage assessed. CO2 containment is quantified by CO2 column height, which describes the amount of CO2 accumulated in the formation underneath seal rock and is controlled by a balance between capillary and gravitational forces acting on formation brine and invading CO2. While previous studies considered only contributions from seal rock (i.e., “nonrelative”), the current study examines a concurrent contribution from reservoir rock as a seal–reservoir “relative” column height since CO2 storage as an analogy to petroleum reservoir is a structural trap consisting of the reservoir and impermeable seal covered. A distinctive discrepancy was found between the resultant relative and nonrelative column heights. The nonrelative column heights were positive (∼3000 m), implying a high potential for CO2 storage. On the contrary, with reservoir rock contribution considered, the relative column heights were negative (∼−1800 m), suggesting CO2 leakage through the structural trap. This was attributed to a relatively larger reservoir pore size (5.72 nm) than that of seal rock (4.04 nm). Hence, the contribution from reservoir rock characteristics is non-negligible when analyzing CO2 storage potential. Owing to CO2 dissolution in formation brine, CO2-induced effects including a geochemical reaction between acidic carbonated brine and rocks were also investigated. Rock dissolutions in both seal (claystone) and reservoir (limestone) rocks were observed with changes in the pore size, leading to lower storage potential. Further attempts to improve the column height were made by hydrophobizing seal rock via surfactant adsorption, although the changes were slight and could only facilitate a possible leakage (less negative height column).

This research aimed to investigate the spatial distribution of arsenic concentrations in shallow and deep groundwaters which were used as sources for drinking and domestic and agricultural uses. A geochemical modeling software PHREEQC was used to simulate equilibrium geochemical reactions of complex water–rock interactions to identify arsenic speciation and mineral saturation indices based on groundwater quality and hydrogeochemical conditions. In addition, the potential health risk from arsenic-contaminated groundwater consumption was assessed based on the method developed by the U.S. Environmental Protection Agency. The study area is located at the western part of the Lampang Basin, an intermontane aquifer, Northern Thailand. The area is flat and situated in a floodplain in the Cenozoic basin. Most shallow groundwater (£ 10 m depth) samples from dug wells were of Ca-Na-HCO3 and Ca-HCO3 types, whereas deep groundwater from Quaternary terrace deposits (30–150 m depth) samples were of Na-HCO3 and Ca-Na-HCO3 types. High arsenic concentrations were found in the central part of the study area (Shallow groundwater: <2.8–35 mg/L with a mean of 10.7 mg/L; Deep groundwater: <2.8–480 mg/L with a mean of 51.0 mg/L). According to geochemical modeling study, deep groundwater contained toxic As (III), as the dominant species more than shallow groundwater. Arsenic in groundwater of the Lampang Basin may have been derived from leaching of rocks and could have been the primary source of the subsurface arsenic in the study area. Secondary source of arsenic, which is more significant, could be derived from the leaching of sorbed arsenic in aquifer from co-precipitated Fe-oxyhydroxides in sediments. Quantitative risk assessment showed that the average carcinogenic risk values were as high as 2.78 × 10−3 and 7.65 × 10−3 for adult and child, respectively, which were higher than the acceptable level (1 × 10−4). The adverse health impact should be notified or warned with the use of this arsenic-contaminated groundwater without pre-treatment.