Abstract: Conventional oil-based drilling fluids are characterized by their significant viscosity effects due to the content of organic clay and asphalt filtration loss controller. So it is difficult to control their rheological properties and the limited low-density oil-based drilling fluids application. Under such circumstances, a clay-free oil-based drilling fluid has been developed by using an independently developed viocosifier, strength-enhancing additives, an emulsifier and polymer filtration loss reducer. Compatibility and optimal volumes of such additives have been determined through experimental study. Research results show that the newly developed clay-free oil-based drilling fluid may have controlled plastic viscosity within 55 mPa·s, an emulsion-breaking voltage above 450 V,an API filtration losses less than 2 mL, cutting pollution resistance up to 30% and water pollution resistance up to 20% under oil/water ratios 70:30 to 100:0, temperature 80-160℃ and densities 0.9-2.2 kg/L. At the same time, the impact of weighting materials on lubrication performance are negligible. The newly developed drilling fluids have been applied in four horizontal shale gas wells in Jiaoshiba Block. Test results show that the innovative clay-free oil-based drilling fluids involve minor raw materials, simplified maintenance requirement, controllable rheological properties and low solid contents. With desirable shear thinning behaviors, the drilling fluid may effectively minimize circulation pressure losses and enhance ROP.