An Improved Approach to Simulate Low-permeability Fractured Reservoirs with Dynamic Hybrid Dual-Porosity Model

Abstract

Abstract It is a challenging work to simulate fractured reservoir from reservoir description stand point, especially low-permeability reservoir with natural/artificial and water-injection-induced fractures. This type of reservoir has been idealized by a set of disconnected matrix blocks within a network of connected fractures such as Dual Porosity model. It is assumed that fracture network is primary continuum for fluid flow, the matrix of low permeability, high storativity is considered to be a sink/source to the fracture. The matrix and the fracture communicate through an exchange term which describes fluid flow between matrix and fracture. It is assumed that the fracture system is in a steady state which does not change during production history. In the development process of low-permeability reservoir with fractures, some phenomena arose different from the above assumptions. Water injection with high injection pressure will induce new fractures. The distribution of natural/artificial fractures will be complicated. The fractures would be open, get bigger in width/length or closed during the production with the variation of reservoir pressure. The above type of fractured systems could usually experience some abnormal phenomena such as high injection pressure in injectors but low pressure in producers at early stage while serious water channeling and high watercut at the medium stage of development. It is difficult to explain these phenomena by existing principles. A dynamic hybrid dual-porosity model is presented for the serious water-channeling phenomena in the fractured low-permeability reservoirs in which dynamic fracture model and psudo-tenser permeability model are overlapped to Dual Porosity model. The fracture network is considered to be in unsteady state in which fracture has possibility to widen, lengthen, close during oil production. A K-tensor is introduced to describe these processes, which is a function of pressure, stress, density of fractures. The paper will detail dynamic hybrid model such as its assumptions, equations, mechanisms and also its applications in low-permeability fractured reservoirs simulation such as in Changqing and Jilin Oilfield.