Abstract: Through addition of blast furnace slag and some chemical agents, a conversion of drilling fluid into cement slurry can be accomplished. The required specifications and optimized selection of slugs, the properties of converted slurry in fluid and setup phase, the chemical additives needed and the conversion technology were figured out in this study. A formulation of MTC fluid with destiny of 1.50~1.70 g/cm3, API filtration under 100 ml, thickening time of 180~300 min and strength over 13 MPa was presented. Successful practices with good quality of five φ244.5 mm casing cementing with this techniques using a MTC fluid with density of 1.62~1.81 g/cm3 were obtained in Jidong oilfield. In comparison with regular cementing method, 75% of cementing material expenses can be saved with application of these techniques.