Use of high HCl concentrations to dissolve Mn3O4-based filter cake will result in corrosive environment and release of poisonous chlorine gas (i.e., strong oxidizer). Thus, removal of deposits formed at the wellbore because of drilling fluids becomes more challenging when dealing with additives (e.g., Mn3O4) that involve complex interactions with the cleaning fluids, especially at high temperatures.

We studied the reaction of HCl with Mn3O4 particles as a function of time. Additionally, we investigated the release of chlorine gas up to reaction temperature of 284°F and 15 wt% HCl. Several techniques and instruments were employed in this study. Solubility of filter cake was examined using a HPHT filter press. GC/MS technique was used for chlorine gas analysis, atomic absorption were used to measure manganese concentrations, and to analyze solids remained after reaction we used x-ray diffraction.

Solubility of filter cake using 10 wt% HCl and temperature of 250°F was 78 wt% (no mixing during the reaction). At 190°F, high concentration of HCl (10 wt%) showed complete solubility of Mn3O4 particles while, 1 and 4 wt% HCl showed ∼70 wt% solubility. Chlorine gas was not dissociated using 4 wt% HCl at 190°F. At 284°F, 5 wt% HCl was enough to release chlorine gas. Therefore, HCl concentrations lower than 5 wt% are recommended and will dissolve most of Mn3O4. The following reaction agrees with the experimental results of 1 and 4 wt% HCl at 190°F:
Mn3O4+4HCl2MnCl2+MnO2+2H2O
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