Abstract
Ilmenite (FeTiO3) with a mean particle size of 30 – 45 um was first introduced into the oil industry as weighting material in 1976. However, its use was limited mainly because of its abrasiveness to drilling equipment. Recently, a superfine ilmenite (5 μm) was introduced to address shortcomings of the traditional weighting materials. The objective of this study is to discuss the performance of oil-based drilling fluids using ilmenite as a weighting material for HPHT applications.
Oil-based drilling fluids with a density of 1.92 SG containing API standard barite and ilmenite were compared. HPHT filtration tests under static and dynamic conditions were conducted at 300°F and 300 psi. Indiana limestone cores with an average porosity of 23 vol% and an average permeability of 100 md were used in the filtration tests. The rheological properties, sag tendency, the volume of filtrate, and the filter cake thickness of the oil-based drilling fluids were determined before and after heating at 400°F for 16 hours.
Results showed that ilmenite-based drilling fluids had a sag factor of < 0.3 and a plastic viscosity of 25–30 cp, much lower than those of barite. HTHP filtration tests showed that under static conditions, the filter cake had a thickness of 0.18 in. and 2.9 cm3 of filtrate volume; while under dynamic conditions, the filter cake thickness was 0.15 in. and the filtrate volume was 2.2 cm3. The rheological properties of oil-based drilling fluids were constant after heating at 400°F for 16 hours. The filter cake thickness and sag factor were small even after 16 hours of heating. This study provides an evaluation of oil-based drilling fluids with ilmenite as a weighting material for HPHT wells, and gives recommendations on how to use it in the field.
