A New Application of Potassium Nitrate as an Environmentally Friendly Clay Stabilizer in Water-Based Drilling Fluids

Abstract

Abstract Currently, the application of potassium chloride (KCl) as a temporary clay stabilizing additive in water-based drilling fluids is challenging in chloride-sensitive formations due to problems with wellbore stability and drilling fluid. Its use can also impose significant additional costs to drilling operations. In addition, the chloride ions can cause contamination, with the potential to inhibit the growth of vegetation and to pollute aquifers. The purpose of this study is to propose a new high-performance water-based fluid system using potassium nitrate (KNO3) instead of potassium chloride as a clay-stabilizing additive for drilling applications. Water-based drilling fluids using potassium nitrate and potassium chloride, respectively, were prepared with a density of 1.3 S.G. using API barite (BaSO4, D50=15-20 μm, S.G.=4.2), manganese tetraoxide (Mn3O4, D50=1 μm, S.G.=4.8), or micronized ilmenite (FeTiO3, D50=5 μm, S.G.=4.5-4.7) as weighting materials. The Capillary Suction Time (CST) test was used to optimize the brine concentration in drilling fluids for effective clay swelling inhibition. High-pressure/high-temperature (HP/HT) filtration tests were conducted under static conditions at 250°F and 300 psi. Berea sandstone cores with an average porosity of 23 vol% and an average permeability of 100 md were used in the filtration tests. The rheological properties, the volume of filtrate and the filter cake thickness generated by the water-based drilling fluids were determined and compared. CST results show that potassium nitrate exhibits characteristics similar to potassium chloride as a clay stabilizer above 4 wt% concentration. The water-based drilling fluid containing potassium nitrate has very similar rheological properties when compared with potassium chloride. The HP/HT filtration press results show that water-based drilling fluid with potassium nitrate has a low filtration volume, less than 1 cm3, and formed thinner filter cake when using API barite as the weighting material. This paper not only highlights the successful replacement of KCl by KNO3 to achieve good rheological properties in water-based drilling fluids, but also shows that KNO3-based drilling fluids are more environmentally friendly than KCl-based drilling fluids.