Structural reliability of casing subjected to annular pressure build-up (APB) in oil and gas wells

Resumo

The work objective is to estimate the probability of rupture in oil and gas well casing subjected to loads induced by Annular Pressure Build-Up (APB) through First-Order Reliability Method (FORM). During the well lifecycle, temperature changes from different operations can lead to pressure variations in annular spaces. These fluctuations may compromise the structural integrity of casing and tubing strings. Due to manufacturing uncertainties, casing may exhibit variations in geometric and material properties. Along with uncertainties in geomechanical rock properties obtained from laboratory testing, these factors affect simulation accuracy. Estimating failure probability provides a more reliable safety metric than deterministic approaches. The methodology includes: i) identifying deterministic and random variables; ii) Application of FORM to estimate casing failure probabilities (burst); iii) sensitivity analysis to rank the influence of input variables; and iv) organizing and interpreting the results. This work contributes by quantifying the casing failure probability under APB conditions and identifying the most influential uncertain parameters for the studied scenario. These insights support better-informed decisions in casing design, aiming to ensure structural integrity under varying thermal and pressure conditions.