Zn(II), Mn(II) and Sr(II) Behavior in a Natural Carbonate Reservoir System. Part II: Impact of Geological CO₂Storage Conditions

Abstract

-Some key points still prevent the full development of geological carbon sequestration in underground formations, especially concerning the assessment of the integrity of such storage. Indeed, the consequences of gas injection on chemistry and petrophysical properties are still much discussed in the scientific community, and are still not well known at either laboratory or field scale. In this article, the results of an experimental study about the mobilization of Trace Elements (TE) during CO 2 injection in a reservoir are presented. The experimental conditions range from typical storage formation conditions (90 bar, supercritical CO 2 ) to shallower conditions (60 and 30 bar, CO 2 as gas phase), and consider the dissolution of the two carbonates, coupled with the sorption of an initial concentration of 10 À5 M of Zn(II), and the consequent release in solution of Mn(II) and Sr(II). The investigation goes beyond the sole behavior of TE in the storage conditions: it presents the specific behavior of each element with respect to the pressure and the natural carbonate considered, showing that different equilibrium concentrations are to be expected if a fluid with a given concentration of TE leaks to an upper formation. Even though sorption is evidenced, it does not balance the amount of TE released by the dissolution process. The increase in porosity is clearly evidenced as a linear function of the CO 2 pressure imposed for the St-Emilion carbonate. For the Lavoux carbonate, this trend is not confirmed by the 90 bar experiment. A preferential dissolution of the bigger family of pores from the preexisting porosity is observed in one of the samples (Lavoux carbonate) while the second one (St-Emilion carbonate) presents a newly-formed family of pores. Both reacted samples evidence that the pore network evolves toward a tubular network type.

Influence of CO2 on the Electrical Conductivity and Streaming Potential of Carbonate Rocks

“…Other authors found porosity variations much higher than our values (Auffray et al, ), between +5% and +15% for gaseous CO 2 partial pressures between 3 and 9 MPa. The solubility of CO 2 is pressure, temperature, and ionic strength dependent.…”

“…According to the Henry law in a CO 2 /H 2 O system, the solubility of CO 2 in water decreases when the temperature increases up to 150 °C under atmospheric pressure (Enick & Klara, ) and increases for temperatures higher than 150 °C. On the other hand, the aqueous solubility of CO 2 is greater at elevated pressure (Rosenbauer et al, ), which may explain the high dissolution rate of calcite in the study of Auffray et al ().…”

Zn(II), Mn(II) and Sr(II) Behavior in a Natural Carbonate Reservoir System. Part I: Impact of Salinity, Initial pH and Initial Zn(II) Concentration in Atmospheric Conditions

“…Those conditions correspond indeed to a minimum of~73 atm and 31°C, where the supercritical CO 2 injected in an aquifer is progressively dissolved and trapped in the reservoir formation, and imply many more dissolution reactions than in atmospheric conditions. Therefore, along with integrity studies and risk assessment investigations, the fate of TE mobilized in such conditions remains to be investigated in terms of the quantity of elements that will be definitively released in the aqueous phase and their competitive behavior regarding adsorption (Auffray et al, 2016), and appropriate mathematical tools have yet to be built to simulate their migration along other natural compartments.…”