Abstract
Abstract Water injection is often used to supply formation energy in low permeability reservoirs. A lot of field data shows that fractures nearby the wellbores may extend hundreds of meters because of the poor injectability which is called water-induced fractures. The presence of these fractures significantly changes the flow of injected water thus affecting the development effects. However, few studies of reservoir numerical simulation methods have been presented to simulate the dynamic changes of fractures in the long-term waterflooding process. This study is based on the embedded discrete fracture model (EDFM) in which the fracture system has less dependence on the grid system. By improving the preprocessing algorithm, fracture growth can be considered in EDFM which is called the dynamic embedded discrete model (dEDFM). This new method provides an innovative idea for fracture propagation simulation by attaching new fracture elements to the original fractures once the failure criterion is satisfied. Meanwhile, there is no need to calculate the stress field once the in situ stress is provided, so the computational efficiency is greatly improved compared with the fluid-solid coupling method. Besides, dEDFM has a flexible way of handling fracture elements, so it is suitable for water-induced fracture simulation. Results show that fracture propagation speed is significantly influenced by matrix permeability, in situ stress, and injection intensity, and if the water-induced fractures propagate faster than the original waterfront movement velocity, changing law of the water content rate rising of production wells in different directions will be different. The contribution of this work lies in that it provides a suitable and efficient way for reservoir engineers to deal with water-induced fractures since the propagation of fractures can be considered when it comes to reservoir numerical simulation, and it is helpful for production data prediction and development adjustment in low permeability reservoirs.
Highlights
Low and ultralow permeability reservoirs play an important role in Ordos Basin where water injection development is one of the most commonly used methods to enhance oil recovery
Traditional reservoir numerical simulation methods cannot satisfy the dynamic changes of fractures in low permeability reservoirs when it comes to water injection development
The model we proposed is based on the framework of embedded discrete fracture model (EDFM) in which each fracture is explicitly characterized
Summary
Low and ultralow permeability reservoirs play an important role in Ordos Basin where water injection development is one of the most commonly used methods to enhance oil recovery. Traditional reservoir numerical simulation methods cannot satisfy the dynamic changes of fractures in low permeability reservoirs when it comes to water injection development. The discrete fracture model (DFM) was used to realize the dynamic changes of fractures [14, 15] but was limited to the complexity of grid division. Analytical fracture models coupling with traditional reservoir numerical simulator were used to simulate water-induced fractures by most scholars; some innovative solutions such as dynamic DFM and dynamic fracture model were proposed in recent years, but shortcomings exist when dealing with fracture propagation. Our work is aimed at efficiently simulating waterinduced fractures during the waterflooding development process in ultralow permeability reservoirs; the dynamic embedded discrete fracture model (dEDFM) is established by improving the preprocessing algorithm of EDFM. We will give an evaluation of the dEDFM and a summary of the main results
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