Polymer liquids are used in the oil industry to improve the volumetric sweep efficiency and displacement efficiency of the oil from a reservoir. Surprisingly, it is not only the viscosity but also the elastic properties of the displacing fluid that determine the displacement efficiency. This may be caused by the ability of a viscoelastic fluid to pull oil out of dead-ends. The main aim of our work is to obtain a fundamental understanding of the effect of fluid elasticity, by developing an advanced computer simulation methodology for the flow of non-Newtonian fluids through porous media. The three phase simulations comprises of a Newtonian, a Non-Newtonian and a solid phase. The results of this simulation will provide very important insights into the imbibition of oil through a porous media for understanding the process of enhanced oil recovery (EOR).
As a first step, we simulate a three dimensional (3D) unsteady viscoelastic flow through a converging diverging geometry of realistic pore dimension using computational fluid dynamics (CFD). The primitive variables velocity, pressure and extra stresses are used in the formulation of models. All the mass and momentum equations are considered and discretised in space and time. The physical and rheological properties of actual polymer solutions used in polymer flooding have been incorporated, where the viscoelastic stress part is formulated using a FENE-P type of constitutive equation, which can predict both shear and elongational stress properties during flow through porous media. A Direct Numerical Simulation (DNS) approach using Finite Volume Method (FVM) with staggered grid has been implemented. The results are compared with previous literature studies and a good agreement for a single phase flow has been observed. The model provides insights into flow characteristics for a range of Deborah numbers.
A newly developed second order Immersed Boundary method (IBM) has been incorporated in the model to mimic model porous media. For the first time a coupled second order IBM approach with non-Newtonian flow dynamics has been performed to study viscoelastic flows through porous structures. The effect of rheological parameters on flow and stress characteristics has also been studied in these model porous media. The simulations provide an insight into 3D flow asymmetry at higher Deborah numbers in a converging - diverging geometry.
Micro-channel experiments are carried out using micro-Particle Image Velocimetry (μ-PIV) techniques to obtain insight into viscoelastic flow. Micro-channels allow us to mimic a random porous media and perform controlled experiments at the same scale of an actual porous media. The velocity and pressure drop profiles from the experiments have been further used to validate the CFD model. The proposed simulations present, for the first time, a detailed computational study of the effects of fluid elasticity on the imbibition of an oil phase. The results can be applied in the field of oil recovery process optimization, smart polymer selection and improving displacement efficiency in reservoirs.
Keywords: Viscoelastic flows, Finite volume method, Immersed boundary methods, Three dimensional flow, Micro channel, Micro-PIV, Polymer flooding, EOR