Abstract: Aimed at the present problem of filtration property and high temperature stability adjusting of high temperature
water base drilling fluid around the world，the polymer fluid loss agent HTP–1 anti 240 ℃ and salts are developed. The result
of gravitational thermal analysis indicates that the pyrolytic temperature of molecule chain of HTP–1 is up to 320 ℃，and has
strong thermal stability. Evaluation results of dropping filtration performance several drilling fluid slurry show that HTP–1
has excellent fluid loss decreasing performance and high temperature（240 ℃），salt（saturated brine）and calcium（0.5%）tolerance，
overmatching congeneric fluid loss additive at home and abroad. The mechanism of action of HTP–1 is studied by
experiments such as adsorption，particle size distribution measuring，colloid stability measuring and compressibility of filter
cake testing，which is as follows：HTP–1（1）adsorbs clay particles fast and in large amounts，its performance is not very much
influenced by salt pH and temperature；（2）observably reduce the permeability and improve compressibility of filter cake before
and after aged sixteen hours under 240 ℃；（3）improves particle size grading and colloid stability of drilling fluid system.

Key words: deep well, high temperature, water based drilling fluid, fluid loss agent, operation mechanism