Abstract
ABSTRACT This research is aimed toward an understanding of the effects of the chemical characteristics and mineral compositions of sandstone and formation water based on saline water-rock-supercritical CO2 interaction simulation experiments. These experiments were conducted to assess whether toxic trace elements could be dissolved and released in formation water from sandstone in a CO2 storage layer after CO2 geological sequestration, thus affecting groundwater quality. The experimental results reveal that the concentrations of Cd and Pb in the water under examination exceeded the national primary drinking standard as a result of saline/fresh water-rock-supercritical CO2 interactions after 40 d of sandstone immersion in saline/fresh water and 20 d of interaction. In addition, the Mn concentration in the saline/fresh water exceeded the national secondary drinking standard after 40 d of sandstone immersion and 20–80 d of interaction. However, Cd, Pb, and Mn were released to a greater extent (in terms of concentration, 2-fold for Cd, 7-fold for Pb, and 1.7-fold for Mn) in the presence of salinity, revealing that salinity may enhance the dissolution of Cd, Pb, and Mn after 20 d of saline water-rock-scCO2 interaction. After a long period of supercritical CO2-sandstone interaction, the trace metals previously mobilized can be immobilized again by an increase in alkalinity due to aragonite dissolution.
Highlights
Global warming caused by increased CO2 emissions into the atmosphere is an international concern
This research is aimed toward an understanding of the effects of the chemical characteristics and mineral compositions of sandstone and formation water based on saline water-rock-supercritical CO2 interaction simulation experiments
The concentration percentages of trace elements extracted from sandstone using 10 mL 0.1 N HNO3 over those digested from sandstone after microwave digestion are listed in Table 1, where it can be seen that Mn is the largest extracted fraction (26.2%), and Ba is the smallest extracted fraction (0.25%) (Table 1)
Summary
Global warming caused by increased CO2 emissions into the atmosphere is an international concern. Kharaka et al (2010)’s laboratory results at the Zero Emission Research and Technology field site, Bozeman, Montana, U.S.A., demonstrated that the concentrations of Ca, Mg, Fe, Mn, and trace elements in both formation water and groundwater were increased during and following CO2 injection. Brine-rock-CO2 interaction experiments conducted for 43 d under high pressure (34.4 MPa) and high temperature (120°C) on sandstone collected from the lower Tuscaloosa Formation, Mississippi, U.S.A., at a depth of 3193 m revealed high release of Pb and Cr exceeding the MCLs by an order of magnitude (Karamalidis et al, 2012; Lu et al, 2012). In most of these studies, only liquid samples were collected to confirm trace elements released into water, despite the fact that CO2 injection into the subsurface environment can clearly induce alterations in rock minerals and changes in the chemical and mineral structure of the rock mass (Rathnaweera et al, 2016)
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