A New Application of Potassium Nitrate as an Environmentally Friendly Clay Stabilizer in Water-Based Drilling Fluid
The application of potassium chloride (KCl) as a temporary clay stabilizing additive in water-based drilling fluids is problematic in chloride-sensitive formations. However, failure to utilize clay stabilization leads to additional costs to drilling operations due to wellbore stability and drilling fluid residual problems. In addition, the chloride ions can be defined as a contaminant in land operations, with the potential to inhibit the growth of vegetation and the potential to pollute aquifers. The purpose of this study is to propose a new, high performance water-based fluid system using potassium nitrate instead of potassium chloride as the 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 various weighting materials. Capillary suction time (CST) test was used to optimize the potassium salt concentration in drilling fluids for effective clay swelling inhibition. HPHT filtration tests under static and dynamic conditions were conducted at 250?F and 300 psi. Berea sandstone cores with an average porosity of 23 vol% and an average permeability of 50 md were used in the filtration tests. The rheological properties, the volume of filtrate, and the filter cake thickness of the water-based drilling fluids were determined and compared.
The CST tests show that potassium nitrate performs comparably to potassium chloride as a clay stabilizer. However, the water-based drilling fluid containing potassium nitrate has better rheological properties than that containing potassium chloride. The HPHT filtration press tests show that water-based drilling fluid with potassium nitrate has a low filtration volume, less than 1 mL out of a total solution of 200 - 250 mL, when using 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 economical as well as environmentally friendly than KCl-based drilling fluids in drilling waste management.