Abstract
We present a multi-level discrete fracture model (MLDFM) to guarantee a robust and efficient solution for naturally fractured reservoir simulation. In MLDFM, we apply a triple continuum model using structured grid for forward simulation where large-scale fractures are represented with numerical embedded discrete fracture model (EDFM) and the secondary fractures are upscaled as third continuum. What makes the triple continuum model different from the previous work is that both the numerical EDFM and the third continuum are treated in a dynamic approach by considering the effect of flow direction on the complex local-scale flow response. For that purpose, we construct a finer unstructured discrete fracture matrix (DFM) grid which represents all fractures explicitly and is conformal to the boundary of coarse structured grid. During a simulation run, we apply a basis function to generate the local boundary conditions at fine scale using the global solution. Benefit from that, we can use a more accurate flow-based approach in the extended local upscaling to re-compute the transmissibility in triple continuum model. Moreover, we apply a local-global upscaling formalism to guarantee dynamically updated local boundary conditions for upscaling. Besides, we present several cases using synthetic and realistic fractured networks to demonstrate the performance of MLDFM. The results prove that the proposed MLDFM approach more accurately captures the flow in complex fractured systems than EDFM solutions by comparing against fine-scale DFM. At the same time, MLDFM is more computationally efficient in comparison with fine scale DFM. • An advanced hybrid model for multiphase flow fractured systems is presented. • The model compared with state-of-the-art Discrete Fracture Model (DFM) and Embedded DFM. • The model provides a better accuracy than EDFM with Equivalent Continuum Model used for complex multi-scale fractures. • A set of benchmarks includes complex synthetic and realistic fractured networks.
Highlights
The field management is always challenging for a naturally fractured reservoir due to the complex structure of the fracture network
A new triple con tinuum model will be introduced where the large-scale fractures are represented with numerical embedded discrete fracture model (EDFM), the middle-scale fractures are rep resented with a third continuum, and the small-scale fractures are ho mogenized into the matrix
Since the length of small-scale fractures is much smaller than the grid-block size, we apply the idea of the hierar chical fracture model (HFM) in the comparison instead of EDFM
Summary
The field management is always challenging for a naturally fractured reservoir due to the complex structure of the fracture network. The DFM utilization usually introduces a significant number of control volumes which reduces the efficiency of the simula tion To address this issue, the Multiple Sub-Region approach (Gong, 2007; Karimi-Fard et al, 2006; Karimi-Fard and Durlofsky, 2012, 2016; Awadalla and Voskov, 2018) was proposed where the matrix elements are aggregated as multiple sub-regions and the fracture elements are upscaled as an integrate fracture network in each coarse block. We propose a novel hybrid model named multi-level discrete fracture model (MLDFM) to improve the modelling capabil ities of considering the effect of flow direction on the complex local-scale flow response For this purpose, we integrate a two-scale flow hierarchy within the naturally fractured reservoir simulation. We test a realistic fracture network to investigate the performance of MLDFM in applied field cases
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