Numerical Simulation Research In Fractured Reservoir Based On Unstructured Hexahedron Grid

This thesis mainly focus on one of the scientific issues in fractured reservoir simulation, which comes from China 12th FIVE major project Numerical simulation research on complex structure well in fractured reservoir(NO.2011ZX05014-004) and national nature science funding project Numerical simulation research in fractured reservoir based on unstructured hexahedron grid model and parallel calculation(NO.51474179). Both the projects are conducted by skate key laboratory of oil and gas reservoir geology and exploitation engineering.Fractures reservoir is an important reservoir type, including half reserve and production from traditional fractured reservoir and the low permeability, tight, CBM and shale gas reservoirs with hydraulic fractures. The technology difficulties of fractured reservoir simulation includes three main points. (1) There may exist the large scale fractures which do not belong to the continuous media. The continuous media model for these fractures could lead to a large error and poor prediction on fluid saturation and pressure distribution. (2)Productivity is sensitive to fractures density, size and location. Structural grid cannot describe the fracture information. (3) Dual porous media is usually applied to treat the large fracture, resulting in large errors. And the structural grid always has numerous grids and decelerate the calculation efficiency.The motivation of this thesis is to apply unstructured hexahedron grid in fractured reservoirs to solve the problems above. Meanwhile, the calculation modular is programmed and test the efficiency and reliability by case study.The main research content and achievements are following below:(1) The math models combined dual porous media and discrete fractures are established to divide the reservoir into continuous media area and uncontinuous media area. This model includes the continuous media model and discrete fractures models to accomplish the description complex flow phenomenon of continuous meida(matrix and small fractures) and uncontinuous fractures.(2) The calculation modular is developed to describe the fluid flow according to the media types and flow regulations. This calculation can simulate Darcy flow in intermediate permeable media, unDarcy flow in low permeable media and high permeable media.(3) The unstructured hexahedron grid is introduced to describe the huge fractures size. Based on the fracture distribution, Paving method is adopted to generate the grid, which is most popular method for unstructural grid generation. This method realizes the crossing fractures, multi fractures, complex wells and reservoir boundary condition grid generation, of which speed is high and astringency is well.(4) Because of the high randomness of the unstructured hexahedron grid numbering, the calculation efficiency is low. The numbering system and information storage researches are studied to improve 2D-3D grid arrangement method, point shaping eliminating method of discrete fracture for optimization of the calculation efficiency.The research achievement is applied in the microcosmic numerical simulation to accomplish the function that the numerical simulation reproduces the physical simulation. Meanwhile, the application in complex fractured reservoirs from Shengli Oil field solved the problems of complex well structure and grid generation. This research has a future to become a powerful tool for fracture simulation in fractured reservoirs, reservoirs with hydraulic fractures and shale gas.