With the development of the oil and gas industry, people started to drill deeper wells to get oil and gas. New weighting materials have been developed to help solve the problem caused by the most commonly used barite. Ilmenite is among one of those with higher specific gravity. It can achieve the same density with adding less weighting materials than using barite. Less solids content in drilling fluid is an advantage in rheological properties. Recently, micronized ilmenite has again been tested in labs, after resolving the abrasiveness and magnetic problem that normal ilmenite created. Due to the composition of ilmenite, iron is likely to precipitate in acidic condition and cause formation damage when using acid to remove the filter cake.
The effectiveness of using lower concentration of hydrochloric acid (HCl) as well as using 7.5 wt% HCl and 7.5 wt% hydroxyethyl ethylenediamine triacetic acid (HEDTA) to remove the filter cake generated by ilmenite water-based drilling fluids were investigated. To prepare the ilmenite water-based muds, a high speed mixer was used. After preparing the fluid, the filter cake was generated by high pressure high temperature (HP/HT) filter press at 300 psi and 250°F on a sandstone core with 2.5 in. diameter and 1 in. thickness. Cores with filter cakes were computerized tomography (CT) scanned. Then, the filter cake was soaked with HCl and HCl + HEDTA for several hours. After removal, cores with remaining filter cakes were CT scanned again and compare with the initial. Solutions after reaction were analyzed by inductively coupled plasma (ICP) to determine different cation concentrations. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was used to analyze the filter cake, as well as the residual filter cake.
The results showed that lower concentration of HCl cannot completely remove the filter cake generated by ilmenite water-based drilling fluids. With limited volume of the acid, higher concentration of HCl, which can increase the initial acid to ilmenite ratio, will be more efficient to remove the filter cake generated by ilmenite water-based drilling fluids
