CO2 and NOx reactions with CO2 storage reservoir core: NOx dissolution products and mineral reactions

Abstract

• Experimental and geochemical modelling of CO 2 NO x reaction with reservoir cores. • Nitrate was the major dissolution product with minor nitrite and ammonia. • Dissolved Si, Fe increased from sandstones, Ca, K, S, Si, Mg, Mn, Fe from mudstone. • Dissolution of chlorite, ankerite, sulphates, muscovite; and Fe oxide precipitation. • Results broadly applicable to sandstone CO 2 stream (or other gas) storage targets. The geological storage of CO 2 is a key component in the energy transition to net zero emissions. Industrial CO 2 streams from combustion, or “hard to abate” industries such as lime, cement, and steel production contain gases such as NO x , SO x , N 2 , H 2 S, NH 3 , or O 2 . These gases can impact the gas stream properties, and when dissolved some can form acids inducing rock reactions, or affect the system redox. The behaviour of NO x and its impacts on reservoir rock during CO 2 storage, however, has received little attention. Experimental reactions were performed with supercritical CO 2 containing 50 ppm NO and reservoir sandstones and mudstone. The solution pH decreased to between 3.2 and 4.8, with an initial increase in dissolved Si, Al, K, Ca, Fe, Mg, Na, and S concentrations. Si and Fe concentrations continued to increase from quartz rich sandstones from trace chlorite reaction during experiments, with Ca, K, and Si stabilising. Dissolved Ca, K, S, Si, Mg, Mn, and Fe continued to increase during the reaction of the mudstone from the reaction of mainly chlorite, ankerite, muscovite, and Ca-sulphate. Corrosion of sulphate minerals and chlorite, movement of kaolinite fines, and Fe-oxide precipitation were observed. A higher dissolved concentration of NO 3 − than NO 2 − was measured during CO 2 /NO experiments, indicating mainly HNO 3 formation over HNO 2 . The concentration of NO 2 − displayed a first order type decline over time and was almost completely removed from solution. Dissolved Fe 2+ potentially enabled reduction of NO 2 − forming Fe-oxides. Geochemical simulations predicted Fe-Mg-chlorite, K-feldspar, and ankerite were the main minerals reacting during experiments, with Fe-oxide precipitation. This study is broadly applicable to industrial CO 2 storage in other sandstone reservoirs where NO x may be co-injected with CO 2, however future studies are needed to broaden the understands for more reactive rock types, gas mixtures, and different storage conditions. CO 2 geological storage studies are also applicable to improve prospects for underground hydrogen, gas, or compressed air storage for renewable energy and energy security.