Field test of amine polymeric alcohol drilling fluid system in Baka block

Extremely thick coal bed appears below the depth of 2500 meters in Baka block, and it covers long well interval. And it is unconsolidated and mixed up with carbonaceous mudstone between beds. The relieved stress after a new borehole is drilled will lead to the wellbore caving and peeling and finally form an approximate elliptic borehole, causing vicious accidents, such as bit bouncing, bit freezing while tripping and even borehole discarding. The anti-sloughing capability of amine polymeric alcohol (AP-1) was evaluated by tertiary recovery test and core socking test, and the formula of amine polymeric alcohol drilling fluid system was also optimized. Indoor research showed that the drilling fluid had strong capability of inhibition and pollution resistance, with plastic viscosity as 24 mPa?s, shear force as 11Pa and permeability recovery value as 81.9%~89.6%. The successful test on Ke21 Ping 1 well indicated that the drilling fluid system with powerful inhibition could effectively solve the collapse of Jurassic coal seam and carbonaceous mudstone, and presented high lubricity. Meanwhile it could improve the penetration rate effectively, and performance well in gaining reservoir protection, controlling drilling fluid rheology, enhancing pollution resistance and reducing the occurrence of complex downhole accidents.