Evaluation and Removal of Formation Damage Caused by Oil-Based Drilling Fluids Weighted with Micronized Ilmenite

Solids found in drilling fluids, particularly weighting materials, can cause significant formation damage due to plugging of pores. This study investigates formation damage caused by using an oil-based drilling fluid system weighted with micronized ilmenite. It also evaluates the solubility efficiency of different acid systems to determine a feasible method for filter cake removal to enhance production from drilled wells. Oil-based drilling fluid systems were prepared, and rheological properties of the fluids were measured. High Pressure/High Temperature (HP/HT) filtration experiments were conducted to investigate filtration behavior and filter cake formation. A coreflood system was used to simulate field-comparable dynamic fluid circulation, measuring permeability damage after fluid filtration for 30 minutes. Varying permeability sandstone cores were used for filtration studies. CT scan analysis was used to investigate the formation damage and quantify the depth of solids invasion. An HP/HT reactor was used to measure the solubility efficiency of micronized ilmenite in different acid systems. ICP-OES, XRF, and XRD techniques were used to describe the solubility reactions. Ilmenite-based and barite-based drilling fluids with a specific gravity of 2.0 were compared during performance evaluation. The PV and YP were measured to be 55 cp and 16 lb/100 ft2 for ilmenite, and 64 cp and 11 lb/100 ft2 for barite, respectively. Static filtration experiments for an ilmenite-based OBM showed a leak-off volume of 1.2 cm3. Formation damage evaluation for a barite-based drilling fluid showed an 11% reduction in a low permeability core, increasing to 40% permeability reduction in a medium permeability core. Ilmenite-based fluids showed no reduction of permeability in both. Overall, micronized ilmenite-based fluids showed better performance compared to micronized barite-based fluids, with less formation damage. Of the acid systems tested, regular mud acid had the highest filter cake solubility of 80% at 200 ̊F and a 10:1 acid to solids ratio, while a mixture of glycolic and citric acids dissolved 30% of the ilmenite-based filter cake. Increased fluid performance compared to micronized barite-weighted fluids suggests particle size is not the only factor causing enhancement and damage reduction. Furthermore, determining the efficacy of solubility of ilmenite-weighted OBM filter cake in organic acids translates to establishing safer, more cost-effective field practices