| dc.description.abstract | Micronized ilmenite (FeTiO3) was reported as a weighting material in drilling fluids to avoid the disadvantages of barite and to reduce abrasion of wellbore completion. In this dissertation, coreflood tests were applied for the first time to determine the removal efficiency of filter cake generated by water-based drilling fluids based on the micronized ilmenite under high-pressure/high-temperature (HP/HT) conditions. The capacity of different acids to dissolve the micronized ilmenite was also evaluated.
Near-wellbore conditions during the drilling fluid injection and the mudcake cleanup process in sandstone and carbonate cores at reservoir conditions were simulated by coreflood tests. Inductively coupled plasma (ICP), computerized tomography (CT) scans, and scanning electron microscopy (SEM) were used to analyze the solubility of iron and titanium, chemical composition of dried mudcake, and internal structure of the core, respectively.
A complete analysis of the particle size and chemical composition of the ilmenite sample was conducted using Coulter Counter, SEM, and X-ray diffraction (XRD). Several solubility tests were conducted under 200ºF to find an optimal solvent to dissolve the micronized ilmenite sample. The solvents include different concentrations of HCl, HEDTA, glycolic acid, formic acid, and a mixture of HCl and HEDTA. An acid solution containing 15 wt% HCl and 8 wt% HEDTA dissolved 98.4 wt% of iron and 76.5 wt% of titanium from the ilmenite sample. It was selected to remove the formation damage and to prevent the iron precipitation in the following coreflood tests.
Coreflood tests were performed under 275ºF on Berea and Bandera sandstone core, respectively. 15 wt% HCl had an excellent performance on the dissolution of iron (FeO) and calcium (CaCO3). In Bandera sandstone, 8 wt% HEDTA successfully prevented the iron precipitation. The permeabilities of Berea and Bandera sandstone have increased by 40% and 35.4% after the acid injection, respectively. Outstanding damage removal efficiency from the coreflood study proved that acid solution containing 15 wt% HCl and 8 wt% HEDTA could be served as an efficient solvent for the ilmenite-based drilling fluids. | en |
