Preparation and Application of a High Temperature Suspension Stabilizing Filter Loss Reducer for Cement Slurries

High formation temperature gradients prevail in the Qinghai Oilfield (Tsaidam Basin). High bottom hole temperatures in deep and ultra-deep wells plus high formation pressures from the over-pressurized formation belts impose rigorous requirements on cement slurries as to their high temperature high pressure (HTHP) filter losses and rheology, the settling stability and mechanical performance after experiencing heat impact. To deal with these situations, a suspension stabilizing filter loss reducer DFS-200 containing temperature-sensitive groups and branched chain structures was developed. Evaluation of the general performance of DFS-200 shows that it can reduce the high temperature filter loss of a cement slurry (with density between 2.10 g/cm³ and 2.30 g/cm³) to less than 50 mL, and the cement slurry still has zero free water, small density difference between the top cement and the bottom cement of less than 0.03 g/cm³, as well as good rheology and thickening performance. The DFS-200 treated cement slurry does not viscosify at low temperatures and does not thin at elevated temperatures. The strength of the set cement develops quickly, the transition time of the static gel strength of the cement slurry is short. The 200℃ × 48 h compressive strength of the set cement is greater than 30 MPa and does not decline. DFS-200 has been used many times in liner cementing operations in Tsaidam Basin and has gained good results, it has provided a technical support to improving the job quality of cementing the deep and ultra-deep wells in Qinghai Oilfield and also to ensuring the borehole integrity.