Research on Nano Inhibition and Plugging Potassium Amine Polysulfonate Drilling Fluid System to Prevent Wellbore Instability in Deep Complex Formations

The wellbore instability caused by complex strata is a common problem in drilling engineering, which not only causes economic losses, but also reduces the field drilling efficiency. This paper has taken Block A of Junggar Basin as an example to explore the causes of wellbore instability in complex strata and establish corresponding solutions. Studying the core samples in this area and analyzing the logging data, it is concluded that the micro-fractures developed in the rock layer of the block provide natural channels for the entry of filtrate. At the same time, the water-sensitive clay minerals in the formation have hydration after encountering the filtrate. By optimizing the composition, the corresponding nano-strong inhibition and strong plugging potassium amine polysulfonate drilling fluid system (NPAP-2) was established. The overall use of asphalt anti-sloughing agent, nano-and micro-scale cracks (gaps) for physical plugging, wetting inversion control surface water absorption, chemical inhibition of internal hydration. The performance test shows that the HTHP water loss of the drilling fluid system is less than 10 mL, the recovery rate of rock sample is more than 86%, the viscosity is reasonable, the expansion rate is more than 89%, and the filtration loss is reduced from 8.0 to 5.0 mL. The results show that the NPAP-2 can reduce the liquid activity to enhance the inhibition, effectively improve the settlement stability of drilling fluid, reduce the filtration and ensure the wellbore stability.