Hematite Filter Cake Removal Using Oxalic Acid: Experimental Investigation

The formation of a filter cake is an essential function of drilling fluids, serving to prevent fluid invasion and maintain wellbore stability. However, its removal after drilling is crucial for restoring reservoir productivity. This study investigates the dissolution and removal of hematite-based filter cakes under various treatment conditions. A series of solubility experiments was conducted to evaluate the influence of acid type, concentration, temperature, particle size, solution pH, and treatment duration. Regained permeability and removal efficiency tests were performed using a treatment solution composed of 10 wt.% oxalic acid and 6 wt.% hydrochloric acid (HCl). Additional assessments included corrosion testing and nuclear magnetic resonance (NMR) analysis to evaluate changes in core porosity. Among the tested acids, HCl demonstrated the highest solubility for hematite, while oxalic acid offered significantly reduced corrosion rates. The combined acid solution achieved a hematite solubility of 3.3 g/100 ml, a filter cake removal efficiency exceeding 99%, and a retained core permeability of 98.6%. NMR results confirmed that the treatment restored the porosity system to near-original conditions. This work demonstrates that the oxalic-HCl mixture offers a highly effective and less corrosive alternative for filter cake removal. The findings support its potential for improving post-drilling cleanup and reservoir performance while mitigating environmental and operational risks.