For many years, barite has been the standard weighting agent in the drilling fluid industry. Its high specific gravity has helped produce mud weights in excess of 19 lb/gal. Its hardness has rendered it easily millable to a particle size that reduces settling and minimizes losses on shaker screens and its adequate inertness has enabled it to be used in a wide range of drilling fluids containing different chemical components. Recently, however, dwindling supplies and increased consumption of premium barite have led to significant price increases across the world and a reduction in specific gravity in most commercial grades. This has led to renewed interest in alternative weight materials. Ilmenite and hematite are two minerals that have been used sporadically in the field. Compared to barite, their higher density impacts both the rheology of the fluids and the settling rate of the weight material. A known issue with these materials is their relatively high hardness, which can give rise to abrasion/erosion in the tubular and surface equipment. Another effect that has not been addressed sufficiently is the magnetic characteristic of these iron oxide-containing minerals which has the potential to affect the operation of direction drilling and some other downhole tools. There have been many studies on the use of ilmenite and hematite as weight agents for drilling fluids. These have dealt with the above issues individually or in a scattered manner. In this paper, we report the results of a comprehensive laboratory study on the application of ilmenite and hematite as weight materials for both water- and oil-based drilling fluids. The study includes the effects of different size grades of the materials on rheology and fluid loss, as well as dynamic and static sag. The paper will present relative abrasiveness of the materials compared to barite as measured by two different methods, and recommend size grades that can minimize the abrasion effects. The paper will also report the results of magnetic property measurements which impact operation of several downhole tools, and compares these with that of barite and several other minerals. To complete the comparative testing of these minerals, the results of heavy metal analysis will also be reported for each test mineral.
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