Numerical Simulation Research Of Reservoir Flooding By Alkaline-Surfactant-Polymer

The ASP(alkali-surfactant-polymer)flooding is one of the EOR(enhanced oil recovery)method in the petroleum engineering.Since the heterogeneity of the reservoir,after the water flooding,the preferential migration passage,which is the main channel of the water,appears and lead to that other area with lower permeability will not been flooded by the water and the oil will become the residual oil.According to the articles,the recovery ratio of water flooding is not more than 40% and that is the reason why third generation EOR method is researched.ASP flooding is one of the chemical flooding EOR method and has been widely used in Daqing oil field in China.After the development of polymer flooding,surfactant flooding,the combination flooding,ASP flooding,is developed.Polymer increases the water’s viscosity,decreases water’s permeability and finally decreases the water-oil mobility ratio to promote the sweep efficiency.Surfactant on the one hand,decreases the interfacial tension,increases the capillary number and finally influence the relative permeability.On the other hand,the surfactant will directly change the capillary pressure.Alkali will have chemical reaction with the acid component in oil and produce the in-situ surfactant.The work of numerical simulation of ASP flooding includes the construction of the mathematical model and the programming to attain the numerical solution.Two-phase(water and oil)six-component(water,oil,polymer,surfactant,alkali,brine)flow equations have been developed,where the oil phase just has oil component and other five components are in the water phase.Darcy’s law is applied and with the initial condition,boundary condition,capillary equations and other constitutive equations the ASP flooding mathematical model is developed.The model considers the adsorption of four flooding components,the relative permeability change resulted by surfactant,the viscosity increase because of the polymer and surfactant,the sensibilities of viscosity and adsorption of water considering brine,the alkali’s in-situ production of surfactant.Finite difference method is applied to discretize the partial differential flow equations.And Newton’s iteration method is used to realize the linearization of the transmissibility parameters such as the relative permeability and the viscosity and to gain the Jacobian matrix of the flow equations.Based on the black oil module of the in-house simulator,the program of the six-component two-phase model is developed using Corresponding polymer modules,surfactant modules,alkali modules have been finished.The result has been compared with the commercial reservoir simulation software Eclipse and similar production dynamics for the same data files have been attained,which confirms the correctness.Using the software the EOR effect of the polymer,surfactant and alkali can be reflected correctly without directly considering the phase equilibrium and an independent chemical reaction model with a better calculation velocity.Many reservoir parameters and production parameters’ sensitivity analysis has been done.The result shows that ASP flooding can enhance the oil recovery of heterogeneous reservoir obviously.The injected concentration of polymer and surfactant and the adsorption characteristics are essential for the ASP flooding method.