Mathematical Simulation Of Casing Pipes Refinement From Radioactive Scales

In this paper, the results of mathematical modeling of casing pipes decontamination from radio-active new mineral forms directly in boreholes using hydrochloric and hydro-silicic-fluoric acids are presented. Modeling for highly and low radioactive coatings on the walls of casing pipes of Anastasievka oil-and-gas deposit was performed using GEMS software, based on the method of Gibbs energy minimization. Calculations have shown that thorianite and goethite, that are present in low-active crusts, detected in casing pipes uplifted from comparatively low depths, are well dissolved in hydrochloric acid, but radiobarite is almost insoluble. For the same acid concentrations, almost all radiobarite of high-active coatings detected in pipes uplifted from considerable depth is dissolved. To evaluate the possibility of decontamination of pipes from radiobarite of low-active coatings, modeling of crust dissolution under the action of H2SiF6 has been performed. The results have shown that for acid concentrations of more than 13 % almost all Ra and Ba are dissolved while all iron and thorium remains in goethite-thorianite solid solution. For the same acid concentration, almost all radiobarite from high-active coatings is dissolved. Therefore, no reagent allows decontamination of pipes from coatings of both types. It seems that successive or simultaneous use of both reagents (HCl and H2SiF6) in certain ratio is required. To clarify this issue, further experimental and model investigations are necessary. The issue of decontamination of casing pipes from galena that is present in high-active crusts also needs to be clarified.