Due to the characteristics of deep burial, abnormal pressure, high bottom hole temperature, and abundant fractures, the tight oil reservoirs in the Leijia block of Liaohe Oilfield have many complex situations such as lost circulation and electrical resistance encountered, which seriously restricts the development of tight oil and gas resources in Leijia. Safe and efficient development. To solve this problem, firstly, the mechanism of the wellbore instability of the tight mud shale in the Leijia block was studied. Then, the formula of the composite salt base fluid was optimized by using the principle of activity balance, and the nano-plugging with core-shell structure was developed in a targeted manner. Finally, a high-performance drilling fluid system with strong plugging, strong inhibition and strong lubrication was constructed. The temperature resistance of the system reaches 150 °C, the primary recovery rate of shale is 97.8%, the permeability is reduced by more than 50%, and HTHP (150 °C) is less than or equal to 8 mL. In the test of Well L77-HX in Leijia block, the accident complexity rate is 0, the success rate of electrical measurement is 100%, the ROP is increased by 40%, the drilling depth is 5000m, and the horizontal displacement is 1783m. This new compound salt high-performance drilling fluid system provides technical support

Keywords: Hole collapse, New compound salt drilling fluid, Activity balance