Research and Application of Key Drilling Technologies in Nappe Tectonics of Xinjiang Region

The nappe tectonics in Xinjiang had been affected by old stratum, complex pressure system, strong heterogeneity. Drilling engineering is faced with problems such as low rate of penetration (ROP), frequent leakage, and long drilling period. According to the theoretical analysis, laboratory and field experiments, a series of key drilling technologies have been formed with the core technologies of optimized design for nappe tectonics drilling engineering, ROP improving for high steep and hard formation, fracture formation leakage prevention and plugging while drilling, and gypsum salt formation safe drilling, and had been successfully applied in the drilling of KPN-1 well, the first deep exploration well in Xinjiang nappe tectonics zone. Based on 3D seismic data, formation lithology data, and adjacent wells data, the prediction method of complex formation pressure and the wellbore design principle for nappe tectonics zone are established. The application of the deviation control technology in drilling high steep and hard formation increased the ROP of KPN-1 well by 30%, and the deviation angle is controlled within 2°. The application of personalized bit with special-shaped cutter in Yingshan Group limestone formation increased the ROP by 90%, and the footage of single bit in lower Qiulitag Group silty dolomite formation increased by 30%. The plugging technology could effectively solve the fracture formation leakage in long well section. The saturated salt water drilling fluid system has good anti-pollution ability and good wellbore instability. These technologies are instructive for the drilling engineering in the hard formation of Xinjiang nappe tectonics zone.