Compared with water-based drilling fluids, oil-based drilling fluids have many advantages such as high temperature resistance, salt and calcium intrusion resistance, wellbore stability, good lubricity, and less damage to oil and gas layers. It is an important means for high-temperature deep wells, high-inclination directional wells, horizontal wells and various complex formations, and can also be widely used as unblocking fluid, perforation completion fluid, workover fluid and heart drive fluid. However, its preparation cost is much higher than that of water-based drilling fluid, and its use often has a serious impact on the ecological environment near the well site, and compared with the use of water-based drilling fluid, the ROP is generally lower. The above shortcomings greatly limit the popularization and application of oil-based drilling fluids. In order to increase drilling speed, low-colloid water-in-oil emulsion drilling fluid has been widely used since the mid-1970s. In order to protect the ecological environment and meet the needs of marine drilling, since the early 1980s, the use of low-toxic water-in-oil emulsified drilling fluids with mineral oil as the base oil has been gradually promoted. At present, all oil-based drilling fluids are rarely used, so what is usually referred to mainly refers to water-in-oil emulsified drilling fluids with diesel oil or low-toxic mineral oil (white oil) as the continuous phase.
