Assessment of Strategies for Numerical Modeling of the APB in Oil Wells

This study aims to study and compare numerical modeling strategies for reproducing the phenomenon of Annular Pressure Build-up (APB) in vertical oil wells, in order to contribute to the development of procedures with higher accuracies. APB occurs due to the tendency of confined fluids filling the annular region between casings to expand in response to thermal variations within the well. This phenomenon is critical in the petroleum industry, especially in deepwater environments, where greater temperature and pressure differentials are present. APB leads to increased stresses on well casings, which can cause structural failures and, in extreme situations, could in human, environmental, and economic losses. Therefore, studying the origins and effects of this phenomenon and considering them during the well design phase are essential to ensure safety and efficiency. Motivated by the significance of the topic and the challenge of reproducing APB analytically, several authors have sought to model the phenomenon and its effects using finite element-based computational software like Abaqus. To achieve the proposed objective, the methodology adopted includes: a) literature review of existing strategies for APB modeling; b) definition of a simplified scenario for reproducing selected strategies; c) comparison of methodologies and results obtained from each; and d) discussion on discrepancies, gaps, and potential improvement opportunities. This study evaluates two modeling strategies in Abaqus, both utilizing fluid cavity interaction to model fluid behavior within a plane axisymmetric analysis. The difference lies in the approach to thermal expansion. While one calculates APB directly from thermal variation, the other does so by introducing an equivalent mass flow. Furthermore, the strategies will be compared not only in terms of results and accuracy, but also with regards to computational cost, aiming to identify the most efficient approach for modeling the phenomenon. Despite methodological differences, both approaches yield similar results, with the second providing the flexibility to model fluids with different behaviors. Thus, this study contributes to understanding and optimizing APB modeling, aiding in the development of more robust and efficient strategies for predicting the effects of this phenomenon.