Water-based drilling fluid is a multi-phase dispersion system composed of bentonite, water (or brine), various treatment agents, weighted materials and drill cuttings. Among them, the average density of bentonite and drill cuttings is 2.6 g/cm3, and they are usually called low-density solid phases; while weighted materials are often called high-density solid phases. The most commonly used weighting material is API barite, which has a density of 4.2 g/cm3. Since bentonite is the most commonly used grouting material in water-based drilling fluids, and it mainly plays the roles of improving viscosity shear, reducing fluid loss, and building walls, it and weighted materials such as barite are also called useful solid phases. The drill cuttings are called useless solid phase. In drilling fluids, various solid control measures should be used to minimize the content of drill cuttings. The dosage of bentonite should also be sufficient and should not be too large, otherwise it will cause the drilling fluid to have excessive shear, seriously affect the mechanical penetration rate, and have a negative impact on the protection of the oil and gas layer.
Oil-based drilling fluid is an emulsion formed by using water droplets as the dispersed phase, oil as the continuous phase, and adding appropriate amounts of emulsifiers, wetting agents, lipophilic solid treatment agents (organic soil, oxidized asphalt, etc.), lime and weighted materials. liquid system. Figures 1-2 and 1-3 show the typical compositions of water-based and oil-based drilling fluids, respectively.
