3 -- Flow-Governing Equations and Mathematical Models3.1 INTRODUCTION; 3.2 THE LAW OF MASS CONSERVATION; 3.3 GOVERNING EQUATIONS OF MULTIPHASE NEWTONIAN FLUID FLOW; 3.4 CONSTITUTIVE RELATIONS; 3.4.1 Saturation Constraint; 3.4.2 Capillary Pressure and Relative Permeability Functi…