DEVELOPMENT AND FIELD APPLICATION OF COMPOUND SALT DRILLING FLUID FOR CORROSION CONTROL

For Jianghan oil field in Qianjiang sag, which contains about one thousand meters of salt, gypsum and mirabilite underground, a saturated compound salt drilling fluid system was used to be compatible with underground salt/gypsum formation. The great amount of Cl-,Ca2+,SO42- and various additives with complicated composition in the saturat-ed compound salt drilling fluid as well as the dissoved oxygen generated under high tempera-ture c3used serious corrosion of drilling tools. The anticorrosion drilling fluid system devel-oped per API PRB1 and API PRl3B, viscosity intensifier and partial filtrate reducer have re-markable anticorrosion property. They are the priority additives for drilling fluid and the test showed that their pH value is controlled at 8~10 preferentially-A compoundable DFP corro-sion inhibitor has been developed based on corrosion feature. 4 well(120°, 3000m)pilot exhib-ited good anticorrosion result with inhibition rate greater than 80°. The drilling tools pulled out from wellbore had smooth and bright surface and no rust occurred during 12 day stay on drilling floor. It has solved the corrosion problem of drilling tools caused by compound salt drilling fluid and has remarkable economic and social effects.