Numerical Simulation Of Fracture-cavity Reservoir Based On Finite Volume Method

The reservoir description and numerical simulation of fracture-cavity carbonate reservoirs have been always treated as difficult.The traditional numerical reservoir simulation of fracture-cavity reservoirs can’t truly reflect the complex fluid flow in the fracture-cavity carbonate reservoirs,and it affects the development program preparation and production adjustment guidance.This paper mainly deals with the flow coupling problem between the unfilled part of cave reservoir and filled part of cave reservoir or fractured reservoir.This paper has conducted the following research:The fracture-cavity reservoirs are classified according to the different flow states of the fluids in different media.The understanding of the reservoir characteristics of the fracture-cavity reservoir contains among which:the matrix reservoir has no permeability and storage capacity;the fractured reservoir has no storage capacity and has permeability capacity and the inner fluid flow can be equivalent to seepage according to permeability tensor method;the cave reservoir has permeability and storage capacity,the fluid flow in the no filling part of cave reservoir belongs to pipe flow and the fluid flow in the filling part of cave reservoir belongs to seepage.So the fracture-cavity reservoir is divided into seepage area and pipe flow area.However,there is an interface between the pipe flow area and the seepage area.The flow state near the interface is a coupled flow or transition flow of seepage and pipe flow,and the coupling interface is difficult to describe.This is the next problem to be solved.The mathematical model of the fracture-cavity reservoir based on the new coupling method is established,and the program preparation and example verification are completed.In the establishment of the single-phase flow and two-phase flow mathematical model of the fracture-cavity reservoir,this paper presents two new concepts which contains grid porous medium occupancy coefficient and coupling region.The improved Stokes-Brinkman equation for adding the grid porous medium occupancy coefficient is used to solve the coupling problem.The coupling area is used to simplify the precise description of the coupling interface.This paper presents grid porous medium occupancy coefficient to describe the boundary of the unfilled cavity and simplify its boundary condition.The oil-water interface is described using the elemental oil saturation in the unfilled cave system,saving the computational cost of interface tracking.Based on the establishment of the mathematical model,using MATLAB language to secondary develop the open source computational fluid dynamics software uFVM,using the staggered grid technology and the Semi Implicit Method for Pressure Linked Equations SIMPLE algorithm to solve the pressure field and speed Field.Then this paper forms a new model solver and links the post-processing program and finally compiles into a fracture-cavity reservoir numerical simulation software.The simulation results of the single-phase flow program are compared with the simulation results in the Beavers-Joseph condition and experimental data from Laser Doppler Velocimetry LDA in the same model.The feasibility of the application of the coupling region and grid porous medium occupancy coefficient is verified.The simulation results of the two-phase flow program are compared with the Eclipse simulation results under the same mechanism model.And the results of the two-phase flow program in describing the flow state of the filled cavities are better,thus verifying the feasibility of the two-phase flow program in the fracture-cavity reservoir.The feasibility of applying this procedure to the actual reservoir is verified by the example of Tahe S48 well’s study.This paper uses the case-proven program to numerical simulation study on water cut law of fracture-cavity reservoir.This paper studies water cut rising law in the production of different combinations of fracture reservoir and cavity reservoir and analyzes the influencing factors of different water cut laws.