Accurate and efficient simulation of multi-phase flow in naturally fractured reservoirs with complex natural fractures is very important for economic development. There are several key methods to perform reservoir simulation with natural fractures such as dual porosity dual permeability (DPDK), embedded discrete fracture model (EDFM) and the combination of EDFM and DPDK. However, each method has its advantages and disadvantages. DPDK cannot model natural fractures explicitly and accurately. However, DPDK is usually more efficient than EDFM. EDFM is more accurate for fracture modeling and simulation. However, the EDFM needs to generate more additional fracture cells than DPDK when modeling large number of fractures, leading to lower computational efficiency than DPDK. In this study, we benchmarked four different methods using the actual field data including EDFM, DPDK, EDFM used to model large fractures and small fractures are upscaled to single porosity model, and EDFM used to model large fractures and small fractures are upscaled to DPDK. The accuracy and efficiency were systematically compared. This study provides key insights for naturally fractured reservoir simulation.

1. Introduction

The presence of a large number of three-dimensional complex natural fractures plays an important role in economic development of naturally fractured oil and gas reservoirs. An efficient reservoir simulation method to model the effect of such complex fractures effectively and accurately on well performance is needed.

Traditionally, the method of dual porosity and dual permeability (DPDK) is often used to model complex natural fractures with high fracture density (Warren and Root, 1963; Kazemi et al, 1976; Blaskovich et al., 1983; Hill and Thomas, 1985). However, this method cannot handle natural fractures explicitly and accurately. In order to properly model any complex natural fractures, we have developed a non-intrusive embedded discrete fracture model (EDFM) method (Xu et al., 2017, 2019; Xu and Sepehrnoori, 2019; Sepehrnoori et al., 2020). It works with both in-house and third-party reservoir simulators with the capability of non-neighboring connections (NNCs) to model fractures using structured grids without the need of unstructured grids. The comparison between EDFM and DPDK methods with the real field data has not been well investigated.

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