Numerical Simulation Of Fractured Reservoirs Based On Finite Element - Finite Volume Method

There are abundant hydrocarbon resources in fractured reservoirs. But it is very difficult to understand the mechanism of fluid flow for the media types, multi-scales and strong heterogeneity. The flowing rules and numerical simulation of fractured reservoir has become a hot and difficult spot. The seepage model of fractured reservoir is mainly divided into three categories:the traditional continuous model and the equivalent continuous medium model and the discrete fracture network model. The traditional continuous model neglects the complex distribution of fractures and matrix blocks. It is applicable to the large macro fractures reservoir. The equivalent continuous medium model converts the fractured reservoir to the permeability anisotropy continuous medium model. It is suitable for a wide range of matrix seepage in large macro fractures reservoir. The distribution characteristic and attribute of each fracture can be taken into account in the discrete fracture network model, and it is applicable to the multi-scales and strong heterogeneity fractured reservoirs.Finite difference method is an absolute dominance for the numerical solution of partial differential equations. Finite difference method is a direct physical approximation theory. It is simple and has clear physical significance. But the application is restricted for the severe grid orientation and the low precision. The finite element method uses the integral "weak" form to handle the partial differential equations. It has high accuracy, and is easy to handle complex boundary. The finite volume method satisfies the local conservation essentially. There are huge advantages to combine the finite element method and the finite volume method.As a result, based on the discrete fracture model, we choose the Galerkin finite element and node-center finite volume method to establish the numerical format. In brief, the works of this paper can be list as follows:(1)Based on the principle of material balance, combined with the motion equation, continuity equation and state equation, deduced the oil-water two phase immiscibility, compressible fluid flow equation;(2)Based on the unstructured grid, we used the Galerkin finite element and node-center finite volume method to establish the numerical format;(3)This paper programmed the FE-FVM numerical simulator for fractured reservoirs, and the seepage numerical equation was solved by the IPMES method;(4)We applied the FE-FVM numerical simulator to simulate the water-flooding performance of fractured reservoirs. The simulator has been proven by examples.The results showed that the existence of the fracture could change the direction and velocity of the waterfront. Compared with the homogeneous reservoir, fractured reservoir had more serious water breakthrough and higher water cut. The remaining oil distributed on both sides of the multi-fracture system.