Abstract: In view of the poor high-temperature tolerance of conventional filtrate reducers for drilling fluid, a cross-linked starch as filtrate reducer with high temperature tolerance for drilling fluid was synthesized by cross-linking reaction method with corn starch taken as raw material and sodium trimetaphosphate as cross-linking agent. As found in the test results, the cross-linked starch prepared by using sodium trimetaphosphate as the cross-linking agent was highly tolerant to temperature; when the mass fraction of cross-linked starch in the drilling fluid was 1.5%, it was still effective in filtrate loss reduction at 160 ℃, with an API filtrate loss of 11.0 mL and a viscosity of 33.5 mPa·s; compared with carboxymethyl starch used as filtrate reducer, this filtrate reducer was distinctly effective in high temperature tolerance without viscosity increase. The results of its application on an appraisal well in Yuanba Block of Southwest Oilfield showed that it effectively reduced the filtrate loss of drilling fluid at 150 ℃, and at the same time controlled the drilling fluid viscosity and improved the overall temperature tolerance of the drilling fluid. The field application effect was excellent. The results of the study can serve as references for the preparation of cross-linked starch as filtrate reducer for drilling fluid.

Key words: filtrate reducer, cross-linked starch, sodium trimetaphosphate, high-temperature tolerance, drilling fluid