Removal of Manganese Tetraoxide Filter Cake Using a Combination of HCl and Organic Acid

Abstract

Summary The removal of filter cake generated by drilling fluids weighted with manganese tetraoxide (Mn3O4) particles may require strong acids [e.g., hydrochloric acid (HCl)]. Organic acids are not efficient with high-density drilling fluids (> 100 lbm/ft3) that contain large amounts of weighting materials (e.g., Mn3O4). A single stage of HCl treatment in a high-temperature and corrosive environment cannot be used. In certain cases, a two-stage treatment is recommended first to degrade polymers, and then to dissolve the solid particles in the filter cake. The reaction of acids with solid particles in the drilling fluids was investigated as a function of time at reaction temperatures up to 250°F. The solubility of the filter cake was examined using a high-pressure/high-temperature (HP/HT) filter press. Gas chromatography was used to analyze produced gases. Atomic absorption was used to measure the ion concentrations in spent acids, and X-ray diffraction was used to analyze solids. A safe, efficient, and economic technique that involves mixing HCl and an organic acid was developed to dissolve the filter cake in a one-stage treatment. The results showed higher removal efficiency (> 85%). The solubility of Mn3O4-based filter cake using 10 wt% HCl at 250°F was 80 wt%, but the reaction released chlorine gas, which is toxic and corrosive. HCl concentrations less than 5 wt%, the release of chlorine gas was not significant, but the solubility of the filter cake was low. Lactic acid alone did not dissolve the filter cake. However, a combination of 4 wt% lactic acid and 1 wt% HCl dissolved Mn3O4 particles completely at 190°F. At a temperature of 250°F, nearly 85 wt% of the filter cake was dissolved. This technique uses lower concentrations of HCl/organic acid, which would reduce the cost of the acids required for the treatment. Using HCl alone is an inexpensive approach but HCl cannot be used at concentrations above 5 wt% with Mn3O4-based filter cake. In addition, a third method was examined to remove the filter cake using a combination of organic acid and enzyme.