Empirical expressions of quartz solubility in H2O, H2O+CO2, and H2O+NaCl fluids
An empirical equation of quartz solubility in H20 at elevated pressures and temperatures (up to 10 kb and 900°C) is obtained based on the published experimental results. The resultant solubility equation is as follows: 1nSwater = -1.51914 + 1.999701npwater 2636.78T-1 + 0.00387766T+ 0.0198582PT-1, where Swater, Pwater, T, and P stand for quartz solubility (mol/kg H20), density (g/cm3) of pure water, temperature (Kelvin), and pressure (bar), respectively. Densities of pure water are calculated by
... r are calculated by the equation of Haar et al. (1984) . The solubility equation is then modified for describing the solubility behavior of quartz in H20 + CO2 or H20 + NaCI fluid. For the modification, this study uses the weight fraction of water in the solvent (F), density of the aqueous fluid (paq), and an empirical constant (O) as the additional terms. The ratio of quartz solubility in aqueous fluid (Saq) to that in pure water (Swater) at the same pressure-tem perature condition is then expressed as ln(Saq/Swater) = Oln(pagF/pwater). Densities of H20 + CO2 and H20 + NaCI fluids are computed with the equations of Kerrick and Jacobs (1981) and Anderko and Pitzer (1993a), respectively. The empirical constant for quartz solubility in H20 + CO2 fluid is 1.49063. For obtaining the constant, this study considers the published experimental results done at 1.5 kb to 5 kb, 600° to 700°C, and up to 71 wt% C02 concentration (mole fraction of CO2 = 0.505). The 0 value for quartz solubility in H20 + NaCI fluid is 3.24740, which gives the calculated solubilities consistent with the experimental results done at 0.2 kb to 2 kb, 200° to 700°C, and up to 33.6 wt% NaCI concentration.