Numerical analysis of mechanical behavior and safety evaluation of controllable blowout prevention process tubing operations after large-scale fracturing

Early pressurized flowback after large-scale hydraulic fracturing increases blowout risk in high-temperature, high-pressure and sand-laden wells. This study proposes a whole-process mechanical evaluation framework for a controllable downhole blowout-prevention workstring consisting of a retrievable hanger packer and a pressure-actuated valve. Finite-element models are developed to evaluate run-in stability under casing constraints, shut-in sealing and anchoring performance based on local nonlinear contact behavior, and load transients during unsetting and fishing under staged displacement and pressure loading. The results indicate stable run-in without unacceptable stress or instability, a self-energizing sealing response under the design differential pressure, and that the shut-in pressure limit is primarily governed by the anchoring anti-uplift capacity rather than the string body strength. Peak hook-load events are concentrated during shear-pin release and elastomer pressure-release. The proposed methodology supports design verification and determination of safe operating windows for post-fracturing well-control operations.