A New Method for Modelling Wellbore Crossflow in Reservoir Simulators

In highly stratified reservoirs, welibore crossflow can have an important impact on reservoir behaviour, and crossflow effects need to be modelled accurately in numerical simulation. The simple approach of shutting in crossflowing layers can lead to incorrect predictions. This paper describes two methods for calculating welibore crossflow in a reservoir simulator. The first model assumes that the fluids in the weilbore are completely mixed, while the second model is a new method based on an exact solution for the fluid composition at each level in the well, using material balance calculations in the wellbore. These methods have been implemented in a generalised compositional simulator, but are equally suitable for black oil models. They can be used with both IMPES and fully implicit solution schemes. The solution of the wellbore equations is decoupled from the main solution algorithm, and does not affect the numerical stability of the simulator. An example is presented to compare results from the two models.