Predicting thermal expansion pressure buildup in a deepwater oil well with an annulus partially filled with nitrogen

Abstract

This article proposes a comprehensive multiphysics routine for calculating Annular Pressure Buildup (APB) in vertical oil wells. The routine couples three key aspects influencing the occurrence of APB: (i) the flow of heated hydrocarbons through the well production tubing, which is accounted for with a multi-component, two-phase hydrodynamic model, (ii) a radial, resistance-based thermal model, which determines the multi-modal heat transfer between the production tubing and the surrounding formation, and (iii) a mechanical model which, when coupled to the previous models, allows the calculation of the APB within each wellbore annulus. The developed routine was compared with actual temperature and pressure field data from a 4,700-m (15,420-ft) deep offshore well composed of three concentric annuli. The innermost annulus (Annulus 1) was partially filled with nitrogen to reduce the buildup of pressure due to thermal expansion. A good agreement is observed between the numerical predictions and the field measurements, which included pressure buildup data for the innermost annulus.