Development and application of embedded discrete fracture model for conventional and unconventional reservoir simulation

Xu, Yifei (Research engineer)
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The simulation of fractured reservoirs is a challenging topic in reservoir simulation owing to the complexity of fracture geometry and recovery processes related to fractured reservoirs. Reliable and efficient numerical models are required for the representation of hydraulic and natural fractures in conventional and unconventional reservoirs. The objective of this work is to develop a numerical approach for simulating complex fractures and complex recovery processes in fractured reservoirs using various types of computational grids. This research is an extension of the Embedded Discrete Fracture Model (EDFM). In this work, methodologies were developed to model various types of 2D and 3D complex fracture geometries. The EDFM was also extended to handle several types of computational grids, including corner-point grids, locally-refined grids, and unstructured grids with mixed elements. Geometrical algorithms were developed and implemented in a general-purpose preprocessing code for the calculation of EDFM connection factors in such grids. The use of the EDFM with matrix grids using various numerical approximation schemes, such as finite-volume method and element-based finite-volume method, was also studied. Furthermore, the model was improved regarding modeling fracture transient flow and dynamic fracture behaviors. For the simulation of hydraulically fractured unconventional reservoirs, various important flow mechanisms were implemented in a compositional simulator. The simulator was used to investigate the relative importance of these mechanisms. The developed methodology was applied to a series of synthetic and realistic case studies. The accuracy of the model was confirmed through comparison with other models for simulating various types of fracture geometries in different hydrocarbon recovery processes. A high computational performance was also achieved using the model. Furthermore, based on the results of this research, for long-term production forecasting, the accuracy of the EDFM is not sensitive to the type of grid, the detailed gridding around fractures, or the numerical approximation scheme, if a similar gridblock size is used in the simulations. For the simulation of short-term flow, the combination of the EDFM with nested grid refinement greatly improves the simulation accuracy for various flow regimes. The modeling of dynamic fracture behaviors and unconventional reservoir flow mechanisms demonstrates the flexibility of the proposed approach in incorporating different physics