Technical countermeasures and analysis on deep well drilling difficulties in Bachu exploration block

Bachu Block is an important exploration and development area of Sinopec in Northwest China, with vast area to be explored, large depth of the well, and few completed wells, and few offset well materials can be taken as the reference in drilling operation. the formation features and drilling difficulties were analyzed in the paper, including palaeogeography, complex and hard lithology, gypsum, mudstone and high pressure salt water existing in some formations, resulting in low penetration rate, tight hole, drill pipe stuck, and hole wall sloughing, etc. The difficulties also lead to high trouble rate and longer drilling cycle. In order to solve these problems, the upper formations were drilled with KCl-polymer drilling fluids, and lower formations were drilled with KCl-polysulfonate drilling fluid. And plugging material screening, bottom hole assembly optimization, and bits optimization for deep formation drilling were also taken as the countermeasures. Through onsite applications, the penetration rate raised significantly, which provided a good example of drilling in this area. The suggestion was also proposed to use a compound drilling mode, gear-down turbine, little bent screw and borehole reforming tools to raise the drilling rate.