Abstract: Weightable surfactant treated preflush for well cementing is a preflush viscosified directly with surfactant micelles instead of inorganic suspending agents or organic polymer suspending agents to render the preflush viscosity and gel strength necessary for the suspending of solid particles. This paper gives a detailed description of the suspending mechanisms of this kind of preflush. The weightable surfactant treated preflush can be used in cement slurries with a variety of densities and has good suspending stability and flow properties. It is resistant to high temperatures up to 150℃. It is compatible with drilling fluids and cement slurries, and its rheology can be changed to satisfy the needs of different work conditions. By controlling the viscosity of the preflush, turbulent flow and plug flow can be achieved in displacing hole fluid, and optimum flushing results can be obtained. The use of this kind of preflush improves the bonding between casing string and cement sheath, and the bonding between cement sheath and borehole wall. The weightable surfactant treated preflush also functions as a spacer in well cementing. Field operations on an extended reach horizontal well and a non-conventional well showed that the rheology of the preflush can be adjusted to satisfy the needs of the operations and to obtain optimum displacement and good well flushing. The preflush had good high temperature anti-settling property, which is helpful in improving the job quality of well cementing and guaranteeing the safety of well cementing operations.