The problem of high friction and high torque is one of the most troublesome problems for engineers in extended reach wells and long horizontal wells. Generally, the friction coefficient of oil-based drilling fluid is around 0.08, while the friction coefficient of water-based drilling fluid exceeds 0.2, which is much higher than that of oil-based drilling fluid. With the increasingly stringent environmental regulations, water-based drilling fluids have gradually become a better choice than oil-based drilling fluids. Therefore, lubricants become a key treatment agent for reducing the friction coefficient of water-based drilling fluids. Although there have been many related studies, there is a lack of comprehensive reviews on environmentally friendly water-based drilling fluid lubricants. In general, water-based drilling fluid lubricants can be mainly divided into solid lubricants, ester-based lubricants, alcohol-based lubricants, and nano-based lubricants. Vegetable oil ester-based lubricants, biodiesel lubricants, and dispersible nano-lubricants are all promising environmentally friendly water-based drilling fluid lubricants. Understanding the lubrication mechanism of different types of lubricants and clarifying the evaluation methods of lubricants is an important prerequisite for the next development in high-performance water-based drilling fluid lubricants. Therefore, the purpose of this paper is to give a comprehensive overview of water-based drilling fluid lubricants in recent years, in order to fully understand the development and lubrication mechanism of water-based drilling fluid lubricants, and provide new ideas for subsequent research on water-based drilling fluid lubricants.
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