Novel Lubricants for Water-Based Drilling Fluids

Abstract

Abstract As drilling in directional and extended-reach wells continues to gain popularity, high torque and drag become increasingly important issues. This is particularly true for water-based muds (WBM), which generally give rise to high coefficients of friction (COF) between the drillstring and the wellbore and, therefore, high torque and drag. In addition, water-based muds can also increase wear rates in the wellbore. For contact between steel and rock, oil-based muds (OBM) and synthetic-based muds (SBM) generally produce COF that are lower than those produced by WBM. However, use of OBM and SBM is severely limited by environmental concerns and high costs. It would be advantageous to identify environmentally friendly WBM that are as lubricious as OBM and SBM. This paper discusses a recent project the aim of which was to find suitable lubricants for WBM that would reduce the COF between drillstring steel and sandstone without having adverse effects on the formation or the environment. Laboratory COF measurements are shown to correlate with simulated field results. Trends in lubricant performance appear to be relatively independent of the type of mud system, although absolute performance decreases with increasing solids content and the presence of other surface-active components. A simple mechanistic lubricity model is described that emphasizes the role played by lubricant-induced wettability changes.