Experimental And Numerical Study Of Fluid Flow Mechanism In Fractured-Vuggy Porous Media

Fractured-vuggy carbonate reservoir with matrix, fracture and vug is well known as extremely anisotropy and heterogeneity, where pore structure is complex and pore size has a large scale. Therefore the fluid flow in fractured-vuggy carbonate reservoir has special properties. Study on fluid flow mechanism in fractured-vuggy porous media has important signification to optimization of oil recovery from such reservoirs. In this dissertation, physical modeling experiment study attaching theoretical analysis and numerical simulation on fluid flow in the artificial fractured-vuggy is presented.First, a group of similarity criterion of physical simulation was derived based on the similarity theory of physical modeling, and simple and practical seven main similarity criterions with specific physical meaning were defined on considering characteristics of fractured-vuggy porous media.The design method of conceptual model considering the simple but concernful factors was put forward according to the property that fluid is almost incapable of permeating and storing in matrix of many fractured-vuggy carbonate reservoirs. Thirty-eight models with different fracture-vug structures were made from marble materials through the self-developed technique of controlling accurately size and configuration of fracture and vug. A set of experimental apparatus for physical modeling experiment was built being equipped with sensor measuring technique and computer automatic control and data acquisition technique. A systems software offering experimental control and data measurement and processing was developed, in which the real-time measuring, acquirement, memory and processing of data were implemented, which include pressure, injection and output flow rate, accumulated mass and volume production, and density and temperature of produced fluid. On account of the experimental process of fluid flow in porous media and on the basic of much experimental practice, a suit of experimental methods and techniques for fluid flow in the fractured-vuggy media was generated, and the physical modeling experiments of one- and two-phase fluid flow were systemically carried out as following.The next, by the experimental results analysis of single phase flow, an empirical formula between permeability of fractured-vuggy media and seven parameters, including fracture density, fracture aperture, fracture roughness, fracture connectivity, vug porosity, porosity and media thickness, were fitted. The results indicate that fracture system is the main factor affecting on permeability and vug system generally wouldn't make the permeability double. At the same time, the effects on the critical velocity of linear and non-linear flow between fracture and fracture, fracture and vug, were respectively analyzed, and the Darcy equation of linear flow and binomial equation, exponential equation and Reynolds equation of non-linear flow were given.Third, the relationships between structure of fractured-vuggy media and the characteristics of oil-water relative permeability curve, water-oil displacement efficiency and water cut variation was respectively analyzed by the experimental results of two-phase flow. Relative permeability curve of water generally shows down concave and it will also show line when the aperture of single fracture is greater than 100μm. The smaller is the fracture aperture and more complex is the net structure, the slower increases the relative permeability of water with water saturation. Water-oil displacement efficiency is low when fractured-vuggy networks are complex, but the structure complexity has smaller effects on the water-oil displacement efficiency with vug porosity increasing. Water-free oil production is high when fractured-vuggy networks are complex, but water cut rises quickly after water breakthrough resulting in low ultimate recovery.The last, the finite element method (FEM) for numerical simulation of linear and non-linear flow of single phase fluid and two-phase flow in fractured-vuggy media were constructed. By the numerical simulation to the typical physical model experiment, it is verified that the developing numerical simulation method is reliable. The variations of pressure, velocity and water saturation in fractured-vuggy media were simulated by FEM,on which influences of correlative parameters were discussed. The results suggest that the existing of vug affects seriously flow law, and gravity has impotent effect on water-oil displacement in vug.The research results lay a solid foundation for well test interpretation, reservoir numerical simulation and development decision of fractured-vuggy reservoirs, and have broad practice value.