Removal of Filter Cake Generated by Manganese Tetraoxide Water-based Drilling Fluids



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Three effective solutions to dissolve the filter cake created by water-based drilling fluids weighted with Mn3O4 particles were developed. Hydrochloric acid at concentration lower than 5 wt% can dissolve most of Mn3O4-based filter cake. Dissolving the filter cake in two-stage treatment of enzyme and organic acid was effective and eliminated the associated drawbacks of using HCl. Finally, combining low and safe concentration of HCl with an organic acid in one-stage treatment was very effective. Hydrochloric acid (10-wt%) dissolved 78 wt% of Mn3O4-based filter cake at 250?F after 28 hours soaking time. However, Chlorine gas was detected during the reaction of 5 to 15-wt% HCl with Mn3O4 particles. At 190?F, 1- and 4-wt% HCl dissolved most Mn3O4 particles (up to 70-wt% solubility). Their reactions with Mn3O4 particles followed Eq. 8 at 190?F, which further confirmed the absence of chlorine gas production at HCl concentrations lower than 5-wt%. EDTA and DTPA at high pH (12) and acetic, propionic, butyric, and gluconic acids at low pH (3-5) showed very low solubilities of Mn3O4 particles. GLDA, citric, oxalic, and tartaric acids produced large amount of white precipitation upon the reactions with Mn3O4 particles. Similarly, DTPA will produce damaging material if used to dissolve Mn3O4-based filter cake in sandstone formation. At 4-wt% acid concentration, lactic, glycolic, and formic acids dissolved Mn3O4 particles up to 76 wt% solubility at 190?F. Malonic acid at lower concentration (2-wt%) dissolved 54 wt% of Mn3O4 particles at 190?F. Manganese tetraoxide particles were covered with polymeric material (starch), which significantly reduced the solubility of filter cake in organic acids. Therefore, there was a need to remove Mn3O4-based filter cake in two-stage treatment. Enzyme-A (10-wt%) and Precursor of lactic acid (12.5-wt%) dissolved 84 wt% of the filter cake. An innovative approach led to complete solubility of Mn3O4 particles when low and safe concentration of HCl (1-wt%) combined with 4-wt% lactic acid at 190?F. HCl (1-wt%) combined with lactic acid (4-wt%), dissolved 85 wt% of the Mn3O4-based filter cake after 18-22 hours soaking time at 250?F in one stage treatment.