Abstract: Borehole wall destabilization has long been a problem that needs to be solved. A high temperature bridging formation stabilizer QFT, has been developed based on the working mechanism under which formation stabilizers are adsorbed on clay particles and formation minerals. Monomers used in synthesizing QFT were AM, AMPS and a strong absorbent monomer M, and potassium persulfate was used as the initiator. The polymerization lasted for 4 hours at 60℃. QFT is a white viscous liquid with 10% active content. The molecular weight of QFT is ca. (8-60)×10⁴ g/mol. QFT is a drilling additive of high inhibitive capacity, good filtration control and weak effect on the viscosity of base mud. The highest temperature for QFT to function is 150℃. Laboratory evaluation and analyses showed that, compared with fresh water, the rate of linear expansion of 3%QFT water solution (tested on shale cores) was reduced by 44.56%, and the percent recovery of shale core in hot rolling test was increased by 34.1% at 150℃. The percent recovery of shale cuttings tested with QFT was greater than KCl, KPAM and FA-367. Cores thoroughly disintegrated in fresh water after soaking for 10 min remained integrity after soaking 24 hours in QFT solution. X-ray diffraction showed that the low molecular weight QFT can enter the space between the crystal layers of clay, thereby prevent water molecules from entering the clay. Base mud treated with QFT had fine clay particles with higher specific surface area, indicating that QFT had been adsorbed onto the surface of clay particles through bridging, and this inhibited the agglomeration of clay particles at high temperatures and ensured that there were fine particles in the base mud to form a thin tight mud cake. The API filter loss of a 4% bentonite base mud treated with 3% QFT was reduced by 48.33% after aging. Drilling fluid containing potassium and calcium, when treated with QFT, had reduced filtration rate. With the same drilling fluid, the percent recovery of shale cores (samples taken from field) was more than 95%, and the strength of artificial cores soaked at 120℃ in the potassium calcium drilling fluid with QFT treatment was 14% higher than the cores soaked in potassium calcium drilling fluid with no QFT treatment. Application of QFT on the well H160 in Hongshanzui demonstrated that potassium calcium drilling fluid treated with QFT successfully inhibited borehole wall instability. Meanwhile, the drilling time of this well was reduced by 43% than the adjacent well H170-X. Monthly drilling rate was increased by 70%, and drilling cost was thus remarkably reduced.