Transient fluid and heat flow modeling in coupled wellbore/reservoir systems
Modeling of changing pressure, temperature, and density profiles in a wellbore as a function of time is crucial for design and analysis of pressure-transient tests (particularly when data are gathered above perforations), real-time management of annular-pressure buildup (ABP) and identifying potential flow-assurance issues. Other applications of this modeling approach include improving design of production tubulars and artificial-lift systems and gathering pressure data for continuous reservoir management. This work presents a transient wellbore model coupled with a semianalytic temperature model for computing wellbore-fluid-temperature profile in flowing and shut-in wells. The accuracy of the analytic heat-transfer calculations improved with a variable-formation temperature model and a newly developed numerical-differentiation scheme. Surrounding formation temperature is updated in every timestep up to a user specified distance to account for changes in heat-transfer rate between the hotter wellbore fluid and the cooler formation. Matrix operations are not required for energy calculations because of the semianalytic formulation. This efficient coupling with the semianalytic heat-transfer model increased the computational speed significantly. Either an analytic or a numeric reservoir model can be coupled with the transient wellbore model for rapid computations of pressure, temperature, and velocity. The wellbore simulator is used for modeling a multirate test from a deep offshore well. Thermal distortion and its effects on pressure data is studied using the calibrated model, resulting in development of correlations for optimum gauge location in both oil and gas wells. Finally, predictive capabilities of the wellbore model are tested on multiple onshore wells experiencing annular-pressure buildup problems. Modeling results compare quite well with the field data and also with the state-of-the-art commercial wellbore simulator.