Predicting the annular pressure behavior during water injection in offshore wells with a transient, multiphysics model

Abstract

Predicting the pressure behavior of annular fluids during production and injection operations in oil wells became a major research topic in the exploration of deep-water reservoirs. Although pseudo-steady-state models can predict annular pressure buildup in most production scenarios, more robust transient approaches are required in injection operations due to the short time scales involved. This paper presents a new transient thermo-structural model that calculates temperature and pressure profiles during a recycled saltwater injection operation in a well with three concentric annuli. The model was compared with field data acquired uninterruptedly for a seven-day period containing two consecutive well shutdowns. The maximum relative deviation between the numerical results and the field down-hole pressure was lower than 4%. Absolute down-hole temperature deviations were smaller than 5 °C. Furthermore, simulations based on a newly proposed dimensionless inter-annular pressure difference parameter facilitated identifying the risk of thermally-induced casing collapse due to contrasting rates of pressure change between neighboring annuli. The effectiveness of mitigating such risks using rupture disks was evaluated numerically, and the most favorable scenario consisted of rupture disks installed in the two casings connecting the three annuli.