The development of naturally fractured reservoirs, especially shale gas and tight oil reservoirs, exploded in recent years due to advanced drilling and fracturing techniques. However, complex fracture geometries such as irregular fracture networks and non-planar fractures are often generated, especially in the presence of natural fractures. Accurate modelling of production from reservoirs with such geometries is challenging. Therefore, Embedded Discrete Fracture Modeling and Application in Reservoir Simulation demonstrates how production from reservoirs with complex fracture geometries can be modelled efficiently and effectively. This volume presents a conventional numerical model to handle simple and complex fractures using local grid refinement (LGR) and unstructured gridding. Moreover, it introduces an Embedded Discrete Fracture Model (EDFM) to efficiently deal with complex fractures by dividing the fractures into segments using matrix cell boundaries and creating non-neighboring connections (NNCs). A basic EDFM approach using Cartesian grids and advanced EDFM approach using Corner point and unstructured grids will be covered. Embedded Discrete Fracture Modeling and Application in Reservoir Simulation is an essential reference for anyone interested in performing reservoir simulation of conventional and unconventional fractured reservoirs. Highlights the current state-of-the-art in reservoir simulation of unconventional reservoirs Offers understanding of the impacts of key reservoir properties and complex fractures on well performance Provides case studies to show how to use the EDFM method for different needs

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

Naturally fractured reservoirs (NFRs) hold a significant amount of the world's hydrocarbon reserves. Compared to conventional reservoirs, NFRs exhibit a higher degree of heterogeneity and complexity created by fractures. The importance of fractures in production of oil and gas is not limited to naturally fractured reservoirs. The economic exploitation of unconventional reservoirs, which is increasingly a major source of short- and long-term energy in the United States, hinges in part on effective stimulation of low-permeability rock through multi-stage hydraulic fracturing of horizontal wells. Accurate modeling and simulation of fractured media is still challenging owing to permeability anisotropies and contrasts. Non-physical abstractions inherent in conventional dual porosity and dual permeability models make these methods inadequate for solving different fluid-flow problems in fractured reservoirs. Also, recent approaches for discrete fracture modeling may require large computational times and hence the oil industry has not widely used such approaches, even though they give more accurate representations of fractured reservoirs than dual continuum models. We developed an embedded discrete fracture model (EDFM) for an in-house fully-implicit compositional reservoir simulator. EDFM borrows the dual-medium concept from conventional dual continuum models and also incorporates the effect of each fracture explicitly. In contrast to dual continuum models, fractures have arbitrary orientations and can be oblique or vertical, honoring the complexity and heterogeneity of a typical fractured reservoir. EDFM employs a structured grid to remediate challenges associated with unstructured gridding required for other discrete fracture models. Also, the EDFM approach can be easily incorporated in existing finite difference reservoir simulators. The accuracy of the EDFM approach was confirmed by comparing the results with analytical solutions and fine-grid, explicit-fracture simulations. Comparison of our results using the EDFM approach with fine-grid simulations showed that accurate results can be achieved using moderate grid refinements. This was further verified in a mesh sensitivity study that the EDFM approach with moderate grid refinement can obtain a converged solution. Hence, EDFM offers a computationally-efficient approach for simulating fluid flow in NFRs. Furthermore, several case studies presented in this study demonstrate the applicability, robustness, and efficiency of the EDFM approach for modeling fluid flow in fractured porous media. Another advantage of EDFM is its extensibility for various applications by incorporating different physics in the model. In order to examine the effect of pressure-dependent fracture properties on production, we incorporated the dynamic behavior of fractures into EDFM by employing empirical fracture deformation models. Our simulations showed that fracture deformation, caused by effective stress changes, substantially affects pressure depletion and hydrocarbon recovery. Based on the examples presented in this study, implementation of fracture geomechanical effects in EDFM did not degrade the computational performance of EDFM. Many unconventional reservoirs comprise well-developed natural fracture networks with multiple orientations and complex hydraulic fracture patterns suggested by microseismic data. We developed a coupled dual continuum and discrete fracture model to efficiently simulate production from these reservoirs. Large-scale hydraulic fractures were modeled explicitly using the EDFM approach and numerous small-scale natural fractures were modeled using a dual continuum approach. The transport parameters for dual continuum modeling of numerous natural fractures were derived by upscaling the EDFM equations. Comparison of the results using the coupled model with that of using the EDFM approach to represent all natural and hydraulic fractures explicitly showed that reasonably accurate results can be obtained at much lower computational cost by using the coupled approach with moderate grid refinements.

Fractured reservoirs have gained continuous attention from oil and gas industry. A huge amount of hydrocarbon are trapped in naturally fractured carbonate reservoirs. Besides, the advanced technology of multi-stage hydraulic fracturing have gained a great success in economic development of unconventional oil and gas reservoirs. Fractures add complexity into reservoir flow and significantly impact the ultimate recovery. Therefore, it is important yet challenging to accurately and effectively predict the recovery from fractured reservoirs. Conventional dual-continuum approaches, although effective in the simulation of naturally fractured reservoirs, may fail in some cases due to the highly idealized reservoir model. The unstructured-grid discrete fracture models, although flexible in representing complex fracture geometries, are restricted by the high complexity in gridding and high computational cost. An Embedded Discrete Fracture Model (EDFM) was recently developed to honor the accuracy of discrete fracture models while keeping the efficiency offered by structured gridding. By dividing the fractures into segments using matrix cell boundaries and creating non-neighboring connections (NNCs), the flow influence of fractures can be efficiently modeled through transport indices. In this work, the EDFM was implemented in UTCHEM, a chemical flooding in-house reservoir simulator developed at The University of Texas, to study complex recovery processes in fractured reservoirs. In addition, the model was applied in commercial simulators by making use of the non-intrusive property of the EDFM and the NNC functionality offered by the simulators. The accuracy of the EDFM in the modeling of orthogonal, non-orthogonal, and inclined fractures was verified against fine-grid explicit fracture simulations. Furthermore, case studies were performed to investigate the influence of hydraulic fracture orientations on primary depletion and the impact of large-scale natural fractures on water flooding processes. The influence of matrix grid size and fracture relative permeability was also studied. Finally, with modifications in NNC transmissibility calculation, the EDFM was applied to the modeling of a multi-lateral well stimulation technology. The accuracy of the modified formulations was verified through comparison with a multi-branch well method. The simulations carried out in this work confirmed the flexibility, applicability, and extensiveness of the EDFM.

As unconventional reservoir activity grows in demand, reservoir engineers relying on history matching are challenged with this time-consuming task in order to characterize hydraulic fracture and reservoir properties, which are expensive and difficult to obtain. Assisted History Matching for Unconventional Reservoirs delivers a critical tool for today's engineers proposing an Assisted History Matching (AHM) workflow. The AHM workflow has benefits of quantifying uncertainty without bias or being trapped in any local minima and this reference helps the engineer integrate an efficient and non-intrusive model for fractures that work with any commercial simulator. Additional benefits include various applications of field case studies such as the Marcellus shale play and visuals on the advantages and disadvantages of alternative models. Rounding out with additional references for deeper learning, Assisted History Matching for Unconventional Reservoirs gives reservoir engineers a holistic view on how to model today's fractures and unconventional reservoirs. Provides understanding on simulations for hydraulic fractures, natural fractures, and shale reservoirs using embedded discrete fracture model (EDFM) Reviews automatic and assisted history matching algorithms including visuals on advantages and limitations of each model Captures data on uncertainties of fractures and reservoir properties for better probabilistic production forecasting and well placement

Recent advances in fracture network characterization have identified high degrees of heterogeneity and permeability anisotropy in conventional reservoirs and complex fracture network generation after well stimulation in unconventional reservoirs. Traditional methods to model such complex systems may not capture the key role of fracture network geometry, spatial distribution, and connectivity on well performance. Because of the ubiquitous presence of natural fractures in conventional and unconventional reservoirs, it is key to provide efficient tools to model them accurately. We extend the application of the embedded discrete fracture model (EDFM) to study the influence of natural fractures represented by discrete fracture network (DFN) models on well performance. Current state-of-the-art modeling technologies have been able to describe natural fracture systems as a whole, without providing flexibility to extract, vary, and group fracture network properties. Our developed implementations analyze fracture network topology and provide advanced mechanisms to model and understand fracture network properties. The first application features a numerical model in combination with EDFM to study water intrusion in a naturally fractured carbonate reservoir. We developed a workflow that overcomes conventional methods limitations by modeling the fracture network as a graph. This representation allowed to identify the shortest paths that connect the nearby water zone with the well perforations, providing the mechanisms to obtain a satisfactory history match of the reservoir. Additionally, we modeled a critically-stressed carbonate field by modeling faults interactions with natural fractures. Our workflow allowed to discretize the hydraulic backbone of the field and assess its influence on the entire field gas production. Our next application applies a connectivity analysis using an efficient and robust collision detection algorithm capable of identifying groups of connected or isolated natural fractures in an unconventional reservoir. This study uses numerical models in combination with EDFM to analyze the effect of fracture network connectivity on well production using fractal DFN models. We concluded that fracture network connectivity plays a key role on the behavior of fractured reservoirs with negligible effect of non-connected fractures. Finally, we performed assisted history matching (AHM) using fractal methods to characterize in a probabilistic manner the reservoir properties and to offer key insights regarding spatial distribution, number, and geometry of both hydraulic and natural fractures in unconventional reservoirs. In this work, we provided computational tools that constitute the foundations to conduct advanced modeling using DFN models in conjunction with EDFM in several reservoir engineering areas such as well-interference, water intrusion, water breakthrough, enhanced oil recovery (EOR) efficiency characterization, and fracture network connectivity assessments. The benefits of our work extend to conventional, unconventional, and geothermal reservoirs

With the recent progress in technologies such as hydraulic fracturing and horizontal drilling, unconventional resource development has exploded in recent years. Nevertheless, significant challenges remain for shale reservoirs because of the extensive number of uncertainties. Without proper characterization processes, extracting economic values from these projects will be difficult, and optimizations for future plans will also be challenging. Therefore, efficient models in production mechanism, management and optimization have gradually become hot topics among the petroleum industry. This study aims to address various crucial challenges during the production process of shale reservoirs, including unconventional well gas oil ratio (GOR) characterization, choke management, and well spacing optimization. Due to the ultra-low permeability and porosity, the fluid phase behavior in shale reservoirs significantly differs from the conventional fluid behavior and increases the production forecasting complexity. A substantial effort to better understand the mechanism is to characterize the unconventional well GOR, which always plays as a critical indicator to help predict long-term oil/gas production trends and develop appropriate production strategies. In this research, GOR behavior was first evaluated by a set of comprehensive sensitivity studies in a tight oil well model, which helped to investigate the key drivers that can impact the GOR response in unconventional resources. Then, a parent-child well-set case in Eagle Ford was presented. Through detailed characterization of the producing GOR, an improved understanding of the parent-child well behavior and the fracture hit impact can be obtained. In order to improve the efficiency of field operation, seeking for proper operation plan has been the focusing topic among the oil and gas industry. Choke management strategy selection is one of the essential measures to regulate fluid flow and control downstream system pressure, which could significantly impact the well production rate and estimated ultimate recovery (EUR). In this study, we utilized the non-intrusive embedded discrete fracture model (EDFM) method to handle complicated fracture designs and predicted the long-term EUR from conservative to aggressive choke strategy. Meanwhile, a series of sensitivity studies were presented to evaluate the impacts of various factors on shale gas production, including fracture permeability modulus, fracture closure level, and natural fractures network. The model becomes a valuable stencil to design fracture closure and complex fracture networks, which is a significant improvement for a more reliable choke management model in unconventional area. Another crucial part for well performance improvement is well spacing optimization. Consistent estimates of well spacing help reduce the impact of complex uncertainties from unconventional reservoirs, thereby improving the EUR and enhancing economic growth. We demonstrated a case study on well spacing optimization in a shale gas reservoir located in the Sichuan Basin in China. By using the advanced EDFM technology, complex natural fractures can be effectively captured and simulated. In this study, five different well spacing scenarios ranging from 300 m to 500 m were simulated individually to find the optimum well spacing that maximizes the economic revenue. As the practicability and the convenience showed in this workflow, it becomes feasible to be utilized in any other shale gas well