Study and Application of a High Performance High Temperature Polymer Drilling Fluid

Laboratory study has been conducted on a high performance high temperature (up to 200℃) polymer drilling fluid which was to be used in high temperature deep well drilling in environmentally sensitive offshore area. The drilling fluid under investigation has LC₅₀ of greater than 10×10⁴ mg/L, and was formulated with a synthetic polymer as the main additive, and auxiliary additives such as nanophase plugging agent, shale inhibitive agent and extreme pressure lubricant etc., which rendered the drilling fluid shale inhibitive capacity and lubricity matching those of oil base drilling fluids. The drilling fluid formulation is environmentally friendly and can be discharged directly into the sea. The experimental results showed that the high temperature seawater drilling fluid, formulated with barite and formates was stable for more than 48 h at 200℃, and had HTHP filter loss of 12-25 mL. It was resistant to the contamination caused by 20% NaCl and 0.5% CaCl₂. 96 h LC₅₀ of brine shrimp by the drilling fluid was greater than 10×10⁴ mg/L. EC₅₀ of luminescent bacteria was greater than 30×10⁴ mg/L.The LC₅₀ and the EC₅₀ values indicate that the toxicity of the drilling fluid conforms to the bio-toxicity requirements of discharging the drilling fluid to Class I sea area. The application of the drilling fluid in oilfields around the Bohai Sea has gained good results; the deepest wells drilled with the drilling fluid was 6,066 m, and the highest bottom hole temperature was 204℃.