poet/bench/barite

Description of barite benchmark

Quick start

mpirun -np 4 ./poet barite.R barite_results
mpirun -np 4 ./poet --interp  barite_interp_eval.R barite_results

List of Files

• barite.R: POET input script for a 20x20 simulation grid
• barite_interp_eval.R: POET input script for a 400x200 simulation grid
• db_barite.dat: PHREEQC database containing the kinetic expressions for barite and celestite, stripped down from phreeqc.dat
• barite.pqi: PHREEQC input script defining the chemical system

Chemical system

The benchmark depicts a porous system where pure water is initially at equilibrium with celestite (strontium sulfate; brute formula: SrSO_4).

A solution containing only dissolved Ba²⁺ and Cl^- diffuses into the system causing celestite dissolution. The increased concentration of dissolved sulfate SO₄^2- induces precipitation of barite (barium sulfate; brute formula: BaSO₄^2-). The overall reaction can be written:

Ba²⁺ + celestite → barite + Sr²⁺

Both celestite dissolution and barite precipitation are calculated using a kinetics rate law based on transition state theory:

rate = -S_m K (1-SR_m)

where the reaction rate has units mol/s, S_m (m²) is the reactive surface area, K (mol/m²/s) is the rate constant, and SR is the saturation ratio, i.e., the ratio of the ion activity product of the reacting species and the solubility constant.

For barite, the reaction rate is computed as sum of two mechanisms, acid and neutral:

rate_barite = S_m (acid + neutral) * (1 - SR_barite)

where

acid = 10^-6.9 exp(\frac {-30800 ⋅ T'} R) * act(H⁺)^0.22

and

neutral = 10^-7.9 exp( \frac {-30800 * T'} R)

R is the gas constant (8.314462 J / K / mol) and T' (K^-1) accounts for temperature dependence of the kinetic coefficients which are experimentally determined at 25 °C or 298.15 K

T' = (1 / K) - (1 / 298.15)

The kinetic rate law as implemented in the db_barite.dat file accepts one parameter which represents reactive surface area in m². For this benchmarks the surface areas are set to

• S_barite: 50 m²
• S_celestite: 10 m²