Study on Quantitative Evaluation Method for Running Risk of Tubular String in Ultra-Deep and Complex Gas Wells

In ultra-deep complex gas wells, due to harsh wellbore conditions and complex tubular string structure, whether the tubular string can safely reach the target formation is a prerequisite for successful completion operations. Aiming at the quantitative evaluation of tubing running risk of ultra-deep and complex gas wells in Sichuan Basin, the calculation model for ultimate hole curvature and tubing string running friction based on three-dimensional wellbore trajectory have been established. In addition, the factors affecting the running of tubing string, such as borehole enlargement rate, fluid performance, pipe wall thickness, friction coefficient and influence law are comprehensively analyzed. The tubing running risk analysis of the typical LX1 well was conducted, and the factors influencing the running risk of tubing string was analyzed. The analysis results showed that the running risk point of tubing in LX1 well is located at a depth of 1260 m. The tubing running risk increases with the increase of wellbore enlargement rate; the running risk of tubing with a rigid downhole tool decreases with the increase of tool length, which will result in the decrease in tubing passing capacity; The critical buckling load of tubing string increases with the increase of the tubing wall thickness, which will result in the increase of tubing running risk; In addition, the running risk of tubing string increases with the increase of fluid viscosity and friction coefficient. Based on the analysis of the influence factors and their laws, a quantitative evaluation method of tubing running risk is established, which will provide theoretical reference for the optimization design of well completion process and equipment in ultra-deep and complex gas wells.