A Dynamic Hybrid Model to Simulate Fractured Reservoirs

Abstract

Abstract Fractured reservoirs simulation has long been challenge to reservoir engineers to handle the complex geometry structure of fractured reservoir and fluid flow processes in it which includes viscous, capillary, gravitational and diffusive effect. In traditional reservoirs simulation, the fractured reservoir is usually divided into matrix and fracture interacting continua such as Dual Porosity model or Dual Permeability model. It is assumed in these models that the fracture system is in a steady state which the width, length, density of the fractures in reservoir does not change during the whole production history, therefore, it is not possible to simulate fractures variation effect with these models. In order to simulate the unsteady state of fracture system, a dynamic hybrid model has been developed in the paper which a dynamic transitivity tensor model is overlapped to Dual Porosity model. It is assumed that the fracture network is the primary continuum for fluid flow, the matrix of low permeability, high storability is considered to be a sink or source to the fracture. The matrix and the fracture communicate through an exchange term which describes the fluidflow between matrix and fracture. The fracture network is considered to be in unsteady state in which fracture has possibility to widen, lengthen, and close during oil production. A transitivity tensor is introduced to describe these processes, which is a function of pressure, stress, density of fractures. The paper will detail the dynamic hybrid model such as its assumptions, equations, mechanisms and also its applications in the fractured reservoirs simulation. The simulation results show that the dynamic hybrid model has high potential to accurately simulate the dynamic fracture network as well as the fluid flow with the capillary, gravitational and diffusive effects between matrix and fracture.