Impacts of polypropylene glycol (PPG) additive and pH on tribological properties of water-based drilling mud for steel-steel contact

In this study, three types of polypropylene glycols (PPGs) were added in basic mud as additives. Different chemicals were added to adjust the pH value of mud. PPGs were found to increase the viscosity and reduce the API fluid loss of original drilling mud. Impacts of PPG and pH value on tribological properties were evaluated for steel-steel contact. Experimental results indicated that lower molecular weight PPG had better friction reduction and anti-wear ability. When excessive amount of PPG was added, friction and wear became worse, which was attributed to the aggregation of hard particles in the basic mud with presence of excessive PPG molecules. In terms of pH, both friction and wear generally increased with pH value of the mud.