Interference of Sodium Chloride on Shale Stabilization with Potassium Chloride in Drilling Fluid

Abstract

The shale formation drilling often generates a wide range of problems if ordinary water-based muds are employed. Furthermore, the alteration of shale formation has complicated the development of adequate drilling fluids. The con­trol of shale instability by the exchange of potassium cations with shale structure is well accepted in the drilling fluid industry. In the cases where seawater or brackish water is used as a base, the presence of Na+ and Cl- in the drilling fluid can disrupt the shale cation exchange process. In this study, KCl fluids with concentrations of 1 to 15 wt% were prepared and analyzed with linear swelling, capillary suction time, and dispersion experiments on shale inhibition property, and then NaCl was added to potassium fluids at different concentrations. The different result of mixed salt fluid and KCl fluids indicated that the presence of sodium chloride could affect the potassium yield in the drilling fluid. Moreover, the low concentration of NaCl/KCl showed better results for shale inhibition, although the increase in NaCl concentration caused high swelling and decreased KCl efficiency in drilling fluid. Ultimately, it was found that the addition of 1 – 5wt% NaCl to 3 – 5wt% KCl was preferable to stabilizing old shale formation. But to drill active and young shale formation, the use of KCl alone in the liquid was recommended.