Abstract: The first viscous-oil horizontal well of Daqing Oilfield-Puqian12-Ping 1 well is located in Puqian block 12 of Heidimiao Oilfield, where there are intensive farmlands, fishponds and grasslands. The construction aims to exploit the reserves which are hard to utilize due to restriction of ground conditions. Technical difficulties of drilling for this well are as follows. Firstly, shallow deflection points of surface ?311 mm boreholes, and deflecting is required from 20 m after drilling, and deflecting drilling will meet 60 m quick sand stratum which features high permeability and easy leakage. Secondly, the stratum of deflecting segment features high mud formation capacity, and shows severe conflict between high drilling speed, high deflecting rate under low displacement and the rock debris taken out, thus indicates high risk of drilling tools being jammed by sand setting. lastly, HI2-3 stratum features shallow buried depth of viscous oil, major oil reservoir shows loosen sandstone bonding, and boreholes are in unstable mechanical properties. There are risks of collapse, leakage and surge in the same stratum during construction. To facilitate oil reservoir identification and interpretation, oil mixture is not allowed in horizontal segment. Therefore, 3 sets of drilling fluid systems are determined on the basis of indoor tests and well structure, and the systems feature reasonable rheological property of drilling fluid, high lubricating, jamming and collapse prevention capacity, and easy discovery of oil and gas show in field application, thus can meet construction requirements for this well.