Application of Safe High-Performance Water Base Drilling Fluid Technology in Zhunzhong Area

Formations in the Zhunzhong (the middle of Junggar Basin) area has complex geological structure; the same hole section penetrates formations with several different pressure systems and the middle and the lower formations are developed with hard and brittle mudstones. The Xishanyao Formation and the Badaowan Formation have joint coal beds and are full of micro fissures which frequently caused sloughing, borehole wall collapse and pipe sticking to happen. Another drilling difficulty is the deep buried reservoirs. Principles of stabilizing the borehole wall and enhancing the rate of penetration were presented based on the analyses the affecting factors and mechanisms of borehole wall instability. A set of water base drilling fluid technology was developed for drilling in the Zhunzhong area safely and efficiently. This technology has been applied on 6 wells in Zhunzhong-1 block and Zhunzhong-4 block, NPT was reduced by 86.74%. Compared with wells previously drilled in the two blocks, the average ROPs were increased by 46.03% and 25.39%, respectively, and the percent hole enlargement was reduced by 69.07% and 45.18% respectively. Using this technology, the goals of stabilizing borehole wall and enhancing ROP have been achieved.