Evaluation of Ilmenite as Weight Material in Drilling Fluids
Authors: Blomberg Nils E. , Melberg Berit 
Published: December 2007

This paper is based on field experiences from two wells and laboratory experiments. Flow-induced abrasion is a considerable problem in the field when ilmenite is used as weight material. In general, field observations are confirmed by laboratory experiments. However, the abrasiveness is highly dependent on the particle size distribution, and experiments clearly show that the abrasiveness of ilmenite can be reduced to that of standard barite by removing the largest ilmenite particles. From our experimental results, we recommend that the size distribution of ilmenite contain fewer than 3% particles greater than 45 microns [45 ]. The use of ilmenite also demonstrated problems with dust. dispersion of ilmenite in water, air entrainment, and foaming, which, as found by laboratory investigations, can be eliminated by reducing the concentration of flotation chemicals. On the basis of field experience and subsequent laboratory studies, we conclude that ilmenite is well suited for use as weight material in drilling fluids since the presently observed disadvantages to a large extent can be diminished.

Introduction

The demand for high-quality barite as drilling fluid weight material is expected to be increasingly difficult to meet. In addition, the supply of barite is geographically limited, with high transportation costs as a consequence in many cases. Because of the expected shortage and possible cost savings, a research program based on Norwegian resources was initiated in Norway in 1975 to investigate possible alternative weight materials. In their study, Haaland et al. found iron-base materials such as ilmenite and hematite to have a good potential for use as weight material. The advantages of ilmenite and hematite as weight material include high specific gravity, solubility in acid, reaction with sour gases, similar or superior fluid properties compared with barite, and availability of large ore deposits. On the basis of this information, Statoil initiated two field evaluations and a subsequent laboratory study during 1979–81 to evaluate ilmenite as weight material. The purposes of the field evaluation were (1) to investigate the overall performance of ilmenite as weight material and (2) to identify problem areas that occur when ilmenite is used. The purposes of the laboratory study were (1) to find, and possibly eliminate, the cause of the observed hydrophobic character of the ilmenite used in the field tests, (2) to evaluate the abrasiveness of ilmenite when used as weight material, and (3) to develop a simple and fast abrasion test applicable for field use. The results of this program give a better basis for evaluating ilmenite for use as weight material in drilling fluids.

Field Experience

Two wells with ilmenite as weight material were drilled in the Norwegian sector of the North Sea in 1979. Both wells were drilled with the same drilling rig, and the total depths and maximum mud weights for Wells A and B were 12,192 ft [3716 m] and 11.7 lbm/gal [1.40 g/cm3], and 9,121 ft [2780 m] and 15.3 lbm/gal [1.83 g/cm3], respectively. Seawater-gel/lignosulfonate mud systems were used in both cases. Typical mud properties at maximum mud weights are given in Table 1. The drilling contractor reported improved rheological properties when ilmenite was used as weight material. Less fine particles, very low attrition rate, and no appreciable settling resulted in a stable rheology with limited need for water dilution and chemical conditioning. Excessive wear was observed in the mud mixing and storage system, whereas no excessive wear or corrosion was found on corrosion rings run in the low-velocity parts of the drillstring. The contractor reported increased change out of pump parts and noticeable wear in the centrifugal pumps. A washout, which could be caused by the use of ilmenite, appeared in a failsafe valve. Fig. 1 is a sketch of the circulating system, with calculated circulation velocities indicated. Visual inspections were carried out throughout the drilling period, and the parts corresponding to 6, 8 and 9 in Fig. 1 were reported to show excessive wear. As can be seen from Fig. 1, this corresponds to high-velocity parts of the circulation system. According to the drilling contractor's report, ilmenite was also difficult to water-wet and disperse, and air entrainment and foaming occurred. In addition, the reports claimed problems with excessive dust in the mud room. The dust adhered to pipes and walls, causing cleaning problems.

JPT

P. 969^