Enhanced oil recovery by polymer flooding and advanced (multi-lateral) wells has been applied to develop China's offshore heavy oil reservoirs. Current commercial simulators lack the ability of modeling polymer flooding processes and multi-segment wells simultaneously, thus limits their application in making reliable production predictions and the overall development plan.
In this work, a black-oil simulator is extended to model polymer flooding by adding brine and polymer pseudo-components to the governing equation. The polymer solution, reservoir brine and the injected water are represented as miscible components of the aqueous phase. Necessary factors have been taken into account for the construction of mathematical model, such as inaccessible pore volume, polymer shear thinning effect, polymer adsorption, and relative permeability reduction factors, etc. These polymer-induced effects, modeled as nonlinear relationships, are based on lab experiments conducted upon core and PVT samples from China's heavy oil reservoirs in Bohai Bay. A fully implicit formulation is applied to solve the governing equations.
In modeling of the multi-lateral wells which are commonly applied in Bohai Bay oil fields, the multi-segment well approach is adopted. The well index (productivity index) is calculated using a 3D projection method based on Peaceman's model. This method is extended to enable its application in both structured and unstructured grid system to fully resolve complex geometrical interaction between multi-lateral wells and the reservoir. The pressure and fluid concentration distribution along wellbores is calculated through the homogeneous model, the result of which can better describe the true physics in the wellbore.
This work, for the first time, provides the development framework to model polymer flooding and advanced wells for EOR in heavy oil fields. Comparing with numerical results from commercial simulators, this model yields better accuracy and more importantly, enables the modeling of polymer flooding processes and multi-segment wells simultaneously.