Experimental Studies of Ilmenite as a Weighting Material in Oil-based Drilling Fluids for HPHT Operations

Ilmenite (FeTiO_(3)), with a mean particle size of 30 - 45 ?m, 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 ?m) 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, which was 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.