Kinetics of calcite dissolution in CO2-saturated water at temperatures between (323 and 373) K and pressures up to 13.8 MPa

Abstract

We report measurements of the calcite dissolution rate in CO2-saturated water at pressures ranging from (6.0 to 13.8) MPa and temperatures from (323 to 373) K. The rate of calcite dissolution in HCl(aq) at temperatures from (298 to 353) K was also measured at ambient pressure with pH between 2.0 and 3.3. A specially-designed batch reactor system, implementing a rotating disc technique, was used to obtain the dissolution rate at the solid/liquid interface of a single crystal, free of mass transfer effects. We used Vertical Scanning Interferometry to examine the texture of the calcite surface produced by the experiment and the results suggested that at far-from-equilibrium conditions, the measured calcite dissolution rate was independent of the initial defect density due to the development of a dynamic dissolution pattern which became steady-state shortly after the onset of dissolution. The results of this study indicate that the calcite dissolution rate under surface-reactioncontrolled conditions increases with increase of temperature from (323 to 373) K and CO2 partial pressure from (6.0 to 13.8) MPa. Fitting the conventional first order transition state kinetic model to the observed rate suggested that, although sufficient to describe calcite dissolution in CO2-free HCl(aq), this model clearly underestimate the calcite dissolution rate in the (CO2 + H2O) system over the range of conditions studied. A kinetic model incorporating both pH and the activity of CO2(aq) has been developed to represent the dissolution rates found in this study. We report correlations for the corresponding reaction rate coefficients based on the Arrhenius equation and compare the apparent activation energies with values from the literature. The results of this study should facilitate more rigorous modelling of mineral dissolution in deep saline aquifers used for CO2 storage.2

A chemical kinetics algorithm for geochemical modelling

“…4.7 presents the calculated concentration of calcium in the CO 2 saturated water while calcite continuously dissolves. These calculations were compared with the experimental measurements of Peng et al (2014) at T ¼ 353 K and P ¼ 13:8 MPa. It can be seen that a good accuracy is achieved for the period of time between 5 min and 1 h for which experimental measurements were available.…”

“…Peng et al (2014) recently determined the dissolution rates of calcite in CO 2 saturated waters far from equilibrium. The following major parallel reactions were taken into account in their study: CaCO 3 ðsÞ þ H þ À!…”

Kinetics of carbonate mineral dissolution in CO2-acidified brines at storage reservoir conditions

“…The rotational angular velocity of the sample was maintained at 73 s -1 for both analogue samples in order to eliminate mass-transfer effects. It was observed that the dissolution profiles for Ketton limestone and North Sea Chalk follow the same trends as found for single calcite crystals (4). The reactive surface area of the sample was obtained by subtracting the pore area from the geometric surface area.…”

“…For each set of measurements, using the rotating disk technique, the angular velocities were increased until a regime where reaction rates were independent of transport limitation was found, as described by Peng et al (4). For calcite, chalk and limestone, allowance was made for variation in pH as the mineral dissolved, according to the software PHREEQC version 3.1.4 (22), but for dolomite and magnesite pH changes were estimated to be negligible.…”

“…In a previous study of calcite dissolution kinetics in CO2-saturated water at reservoir conditions, Peng et al (4) demonstrated that far from equilibrium surface reaction rates, r, can be described by a simple model that accounts for the contributions of reactions 1 and 2 only:…”