Experimental and Modelled Reactions of CO2 and SO2 with Core from a Low Salinity Aquifer Overlying a Target CO2 Storage Complex

Julie K Pearce,Grant K.W Dawson,Suzanne D Golding,Silvano Sommacal

doi:10.3390/geosciences9120513

Abstract

CO2-induced reactions in low salinity aquifers overlying CO2 storage sites are of interest to understand potential reactions or impacts in the possible case of a leak. Previous investigations of overlying aquifers in the context of CO2 storage have focused on pure CO2 streams, however captured industrial CO2 streams may contain ancillary gases, including SO2, O2, NOx, H2S, N2, etc., some of which may be more reactive than CO2 when dissolved in formation water. Eight drill cores from two wells in a low salinity sandstone aquifer that overlies a target CO2 storage complex are characterised for porosity (helium, mercury injection, or micro CT), permeability, and mineral content. The eight Hutton Sandstone cores are variable with porosities of 5.2–19.6%, including carbonaceous mudstones, calcite cemented sandstones, and quartz rich sandstones, common lithologies that may be found generally in overlying aquifers of CO2 storage sites. A chlorite rich sandstone was experimentally reacted with CO2 and low concentrations of SO2 to investigate the potential reactions and possible mineral trapping in the unlikely event of a leak. Micro CT characterisation before and after the reaction indicated no significant change in porosity, although some fines movement was observed that could affect permeability. Dissolved concentrations of Fe, Ca, Mn, Cr, Mg, Rb, Li, Zn, etc., increased during the reaction, including from dissolution of chlorite and trace amounts of ankerite. After ~40 days dissolved concentrations including Fe, Zn, Al, Ba, As and Cr decreased. Chlorite was corroded, and Fe-rich precipitates mainly Fe-Cr oxides were observed to be precipitated on rock surfaces after experimental reaction. Concentrations of Rb and Li increased steadily and deserve further investigation as potential monitoring indicators for a leak. The reaction of chlorite rich sandstone with CO2 and SO2 was geochemically modelled over 10 years, with mainly chlorite alteration to siderite mineral trapping 1.55 kg/m3 of CO2 and removing dissolved Fe from solution. Kaolinite and chalcedony precipitation was also predicted, with minor pyrite precipitation trapping SO2, however no changes to porosity were predicted.

Highlights

Owing to international interest in existing and potential CO2 storage sites in deep saline aquifers, the majority of experimental CO2 –water–rock reactions have been performed in brines and with pureCO2
This study has shown that low salinity aquifers overlying CO2 storage sites may be very variable in porosity, permeability and mineral content
A chlorite rich sandstone showed no measurable increase in micro Computed Tomography (CT) porosity when reacted with CO2 and low concentrations of SO2 over experimental timescales

Summary

Introduction

Owing to international interest in existing and potential CO2 storage sites in deep saline aquifers, the majority of experimental CO2 –water–rock reactions have been performed in brines and with pure. A controlled shallow injection of CO2 into the Zert field site (MT, USA), was performed and resulted in a rapid pH decrease, and increases of Fe, Mn, Mg and Ca concentrations from mineral dissolution, desorption and ion exchange [1]. Associated experiments were used to determine that calcite and dolomite dissolution, with clay or Fe-oxyhydroxide ion exchange and desorption, and Mn oxyhydroxide dissolution and reduction were metal sources; where Mn was correlated with Ca, and. The main source of metals was determined to be from calcite dissolution, even though higher concentrations were sometimes present in pyrite or clays. Batch experiments and geochemical modelling were performed for the low salinity

Methods

Results

Discussion

Conclusion