Solid-free drilling fluid has more advantages as a new type of drilling fluid compared with traditional drilling fluid, such as improving drilling efficiency, protecting oil and not having clay particles clog the oil and gas layer. In this study, Zn/Cu/Fe-doped magnesium-aluminum hydroxide (Mg-Al MMH) was prepared using the co-precipitation method and evaluated in solid-free drilling fluid. The inhibition mechanism of synthesized hydroxide was analyzed by X-ray diffraction, laser particle-size analysis and thermogravimetric analysis. The samples were directly used as drilling fluid base muds for performance evaluation. The results showed that the linear expansion rate of 4% M6-Fe was only 12.32% at room temperature within 2 h, that the linear expansion rate was 20.28% at 90 °C and that the anti-swelling rate was 81.16% at room temperature, indicating that it has a strong inhibition ability at both room temperature and at high temperatures. Meanwhile, the possibility of multi-mixed metal hydroxide as a drilling fluid base mud is discussed in this study. We found that 4% M6-Fe exhibited low viscosity, a high YP/PV ratio and high temperature resistance, and its apparent viscosity retention rate reached 100% rolled at 200 °C for 16 h, with a YP/PV ratio of 2.33.
Keywords: bentonite; drilling fluid; inhibitors; multi-mixed metal hydroxide.