A Semianalytical Thermal Multiphase Wellbore-Flow Model for Use in Reservoir Simulation

Abstract

Summary The detailed interactions between the reservoir and the wellbore are especially important in thermal processes such as steamflooding and in-situ upgrading. These linkages, therefore, must be captured in thermal simulations. Although fully coupled thermal wellbore-/reservoir-flow simulators have been developed, the implementation of the thermal well model is somewhat complicated, and the simulations are computationally demanding. In this paper, we present a semianalytical treatment that enables the extension of existing isothermal wellbore-flow models to the nonisothermal case. The procedure entails the use of analytical solutions for wellbore temperature applied in conjunction with numerical solutions of the reservoir mass- and energy-balance equations coupled with wellbore mass- and momentum-balance equations. The approach thus enables a degree of decoupling between the wellbore flow and energy problems. We proceed by first presenting analytical solutions for wellbore temperature, developed under various assumptions (these basic solutions have been obtained previously). We then describe the use of one of these solutions, which allows for general variation of in-situ phase fraction and other properties along the wellbore, within the semianalytical context. The implementation of the overall method into a general purpose research simulator is also described. Results are presented for several cases involving multiphase flow in monobore and multilateral wells. Close agreement with reference solutions, obtained from a fully coupled thermal wellbore/reservoir model, is demonstrated for all of the examples. The semianalytical treatment is additionally shown to provide comparable or improved computational efficiency relative to the fully coupled model.