Research on the Influence Characteristics of Pitting Damage on the Stress of Downhole Tubular Columns

Abstract

Production gas well tubing is long-term exposed to harsh corrosive environments, and pitting damage has become one of the main forms of tubing failure, seriously threatening the safe production of oil and gas fields. In response to the failure problems of tubing surface multi-pitting damage and under the action of complex loads in actual working conditions, this paper adopts a method combining finite element numerical simulation and fracture mechanics theory analysis to systematically study the influence of pitting damage on the stress distribution, load-bearing characteristics and failure mechanism of downhole tubing. The research shows that the depth of a single pitting pit is significantly positively correlated with stress concentration, while the hole diameter is negatively correlated with equivalent stress when the depth remains unchanged. For multi-point overlapping damage, the smaller the axial distance between the two holes, the more significant the stress concentration, while the radial distance has a smaller impact on the equivalent stress. In addition, under various loading conditions such as tension, internal pressure and external pressure, the increase in the number of pits will significantly intensify the stress concentration phenomenon and greatly reduce the ultimate load-bearing capacity of the tubing. Theoretical analysis further reveals that pitting damage leads to tubing failure through inducing crack initiation and propagation as well as weakening the effective load-bearing cross-section, ultimately resulting in tensile fracture and collapse. The results of this study provide important theoretical basis for the corrosion protection, remaining life assessment and structural safety design of gas well tubing.