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

Abstract

We report experimental measurements of the dissolution rate of several carbonate minerals in CO2-saturated water or brine at temperatures between 323 K and 373 K and at pressures up to 15 MPa. The dissolution kinetics of pure calcite were studied in CO2-saturated NaCl brines with molalities of up to 5 mol·kg -1. The results of these experiments were found to depend only weakly on the brine molality and to conform reasonably well with a kinetic model involving two parallel first-order reactions: one involving reactions with protons and the other involving reaction with carbonic acid. The dissolution rates of dolomite and magnesite were studied in both aqueous HCl solution and in CO2-saturated water. For these minerals, the dissolution rates could be explained by a simpler kinetic model involving only direct reaction between protons and the mineral surface. Finally, the rates of dissolution of two carbonatereservoir analogue minerals (Ketton limestone and North-Sea chalk) in CO2-saturated water were found to follow the same kinetics as found for pure calcite. Vertical scanning interferometry was used to study the surface morphology of unreacted and reacted samples. The results of the present study may find application in reactive-flow simulations of CO2-injection into carbonate-mineral saline aquifers.

Pore‐Scale Dissolution by CO2 Saturated Brine in a Multimineral Carbonate at Reservoir Conditions: Impact of Physical and Chemical Heterogeneity

“…If we assume that the mineral grains forming the core sample are spherical, then the reaction rate constant can be estimated using k = πr/nL where r is the mineral reaction rate with units of moles/(m 2 s), L is the core sample length, and n is the moles of mineral per unit rock volume (Menke et al, ): ρ mineral is the mineral density (2,820 kg/m 3 for dolomite and 2,710 kg/m 3 for calcite), M mineral is their molecular mass (0.1844 kg/mol for dolomite and 0.1001 kg/mol for calcite), and f mineral is the dolomite or calcite mineral fraction in the total sample bulk volume. Using the above estimate of reaction rate constant, equation can be rewritten in the following manner (Al‐Khulaifi et al, ): r mineral is the intrinsic (nontransport limited) reaction rate of each mineral measured from batch reaction experiments at the same reservoir conditions as in our experiments: 5.1 × 10 −5 mol/m 2 s for dolomite and 8.1 × 10 −4 mol/m 2 s for calcite (Peng et al, ; Peng et al, ). Damköhler numbers were calculated in relation to both dolomite and calcite minerals individually using equation .…”

“…r mineral is the intrinsic (nontransport limited) reaction rate of each mineral measured from batch reaction experiments at the same reservoir conditions as in our experiments: 5.1 × 10 −5 mol/m 2 s for dolomite and 8.1 × 10 −4 mol/m 2 s for calcite (Peng et al, 2015;Peng et al, 2016). Damköhler numbers were calculated in relation to both dolomite and calcite minerals individually using equation (4).…”

A review of geochemical–mechanical impacts in geological carbon storage reservoirs

“…For example, over a wide range of pH (2–8), salinity (0–2.5 M), and (0–103.8 bar) values, olivine dissolution rates were found to depend only on proton activity (i.e., ) . Similarly, over a range of temperatures (50–100°C) and salinities (0–5 M NaCl) at 15 MPa, dissolution or pure calcite depended only on proton and carbonic acid activity, whereas dissolution of a limestone and a chalk sample depended only on proton activity …”

“…65 Similarly, over a range of temperatures (50-100°C) and salinities (0-5 M NaCl) at 15 MPa, dissolution or pure calcite depended only on proton and carbonic acid activity, whereas dissolution of a limestone and a chalk sample depended only on proton activity. 66,67 Dissolution reaction rate constants for several minerals are listed in Table 1; they were compiled in a recent paper. 62 Carbonates (e.g., dolomite, calcite, and siderite) are particularly reactive and readily dissolve at low pH (highest k H values).…”

Brine chemistry effects in calcite dissolution kinetics at reservoir conditions

“…Microscopic techniques such as atomic force microscopy (AFM) and vertical scanning interferometry (VSI) allow for the direct observation and quantification of surface dissolution processes (Arvidson et al, 2003;Ruiz-Agudo and Putnis, 2012;Shiraki et al, 2000). On the other hand, bulk dissolution measurements such as those performed in rotating disk reactors (Boomer et al, 1972;Peng et al, 2016;Peng et al, 2015;Pokrovsky et al, 2009a;Pokrovsky et al, 2009b;Rickard and Sjoberg, 1983) are suitable for investigations under well-defined hydrodynamic conditions and at reservoir temperatures and CO2 pressures. In the aforementioned studies, changes in solution composition were monitored as a function of reaction time, resulting in an average rate for all surface sites.…”