Synergistic Effect of Polyaspartate and Polyethylene Glycol on Lubrication Performance of the Water-Based Drilling Mud

[Image: see text] The poor lubrication performance of water-based drilling mud hinders its application in the drilling process of extended, reach horizontal wells. To overcome this shortcoming, polyaspartate (PA) and poly(ethylene glycol) (PEG) were used to improve the lubrication performance of the water-based drilling mud. The conventional performances, lubrication performance, and micro-image of antiwear steel balls of the modified water-based drilling mud were analyzed. The results show that the coefficient of friction (COF) of the water-based drilling mud mixed with 10% PA and 5% PEG was the lowest, reaching 0.094, the reduction rate of COF was 63.1%, and the drilling mud cake stuck factor was also the lowest. The addition of PA and PEG had no effect on the rheological properties of water-based drilling mud and also can significantly reduce the filtrate volume; the reduction rate of the filtrate volume reached 43.5%. All of these result from the synergistic effect of PA and PEG; they are adsorbed on the metal surface and the mud cake to form a lubricating film. At the same time, the lubricants also changed the appearance of the solid particles in the mud cake, which reduced the friction between the mud cake and the drilling tool. Moreover, effects of the influence of drilling mud properties on lubricants (alkali metal ions, pH, temperature, and drilling mud density) were examined. The water-based drilling fluid with the synergistic effect of PEG and PA shows similar lubrication performance as the oil-based drilling fluid and can meet the technical requirements of corresponding horizontal wells.