Paper presented at International Petroleum Technology Conference, Beijing, China, March 2013.
Properties of Ilmenite Water-Based Drilling Fluids for HPHT Applications
Barite is the most common weighting material for drilling fluids, which contain several heavy components including lead, cadmium, mercury, and arsenic. Some of these heavy materials can discharge into the sea, which is not allowed especially in the case of oil-based drilling fluid. The supply of barite is geographically limited, with high transportation costs. To overcome the high cost, shortage, and common problems of barite, an alternative weighting material, ilmenite (5 µm), is introduced which is heavier than barite and more stable at high temperature. Also, the micronized ilmenite was introduced to overcome the ECD challenges in some drilling operations at reasonable cost. Extensive lab work was done in order to: optimize the rheological properties of the drilling fluid; determine the optimum pH that gives stable dispersion; assess the thermal stability,; optimize the filtration parameters (filtrate volume and filter cake thickness), and; characterize the ilmenite-based filter cake. Zeta potential results showed that ilmenite was stable when mixed with water at a pH above 7 and it was dispersed and stable when mixed with the drilling fluid components. Drilling fluids have a density range from 100 to 120 pcf and a plastic viscosity of 28–32 cp. The optimized water-based drilling fluid formula had a small filtrate volume (12 cm3) and thin filter cake (0.2 in.) under dynamic conditions. SEM analysis showed that ilmenite filter cake was heterogeneous and contained ilmenite particles in the layer closer to the rock surface. The kem-seal plus had a big effect to control the rheological properties of the drilling fluid at 350°F. This study will provide a complete evaluation of the drilling fluids with ilmenite as a weighting material and will help drilling engineers to better design drilling fluids for HPHT wells.