Parametric analysis of water injection in an offshore well using a semi-transient thermal-structural model

This paper presents a parametric analysis of the influence of the recycled water injection temperature and flow rate on the pressure differences between the concentric annuli of an offshore injection well using a semi-transient, thermal-structural model. The model is validated against field data, showing average relative deviations from the pressures and temperatures measured at the permanent downhole gauge (PDG) of 5% and 3%, respectively. To enable a clear assessment of the contributions of the independent variables on the inter-annular pressure behavior and, consequently, on the risk of casing failure over a wide range of conditions, the numerical results are presented in terms of dimensionless quantities involving the casing strength. The results indicate a stronger influence of the injection temperature on the magnitude of the inter-annular pressure difference (one of the root causes of casing failure). In contrast, the flow rate controls the trapped fluid cooling rate and, therefore, the rate of pressure change inside the annuli. Finally, aiming at identifying injection conditions that mitigate the risk of casing failure, the modeling framework is employed to simulate intermittent (cyclic) injection scenarios with variable periods of sustained injection and interrupted flow. Using synthetic input data, different combinations of injection/shut-in intervals reduced the pressure difference between neighboring annuli by as much as 11.5%.