Assessment of kinetic conditions of quartz geothermometer application: experiment and modeling

A quartz geothermometer (QG) allows you to determine the temperature of a geothermal reservoir (GR) located at depth by the concentration of SiO2 (m) in a solution that ascends from this reservoir to the surface. An error was made in the initial modeling of QG, which underestimated the quartz deposition rate and thus expanded the scope of application of QG. Another disadvantage of early modeling was that it ignored the possibility of precipitation of metastable modifications of silica. To eliminate these shortcomings, a new mathematical modeling using the finite difference method was performed using new kinetic data. The reliability of the data was assessed by using them in modeling the slow cooling of the quartz–water system and comparing the simulation results with the experimental results of this process. The best agreement between experiments and calculations was obtained when two-stage SiO2 deposition was used in calculations, when different kinetic constants were used above and below the solubility of amorphous silica (AS), which described the deposition of AS and other metastable modifications of silica, respectively. The results of the new QG simulation using new kinetic data were the same with the same ratio of the two initial parameters that characterize the deposition surface area normalized to the mass of water (S/M) and the rate of solution rise (v). The real boundary values of this ratio, S/M and v, are determined, at which the model predicts the correct readings of QG for different temperatures of the solution in GR and at the surface. The kinetic equations used in the simulation do not take into account many features of the silica deposition reaction mechanism. An experimental study of these features will make it possible to perform a more realistic simulation of QG, close to real natural processes.