Streamline tracing and applications in embedded discrete fracture models

Equivalent fracture models are widely used for simulations of groundwater exploitation, geothermal reservoir production, and solute transport in groundwater systems. Equivalent permeability has a great impact on such processes. In this study, equivalent permeability distributions are investigated based on a state-of-the-art numerical upscaling method (i.e., the multiple boundary method) for fractured porous rocks. An ensemble of discrete fracture models is created based on power law length distributions. The equivalent permeability is upscaled from discrete fracture models based on the multiple boundary method. The results show that the statistical distributions of equivalent permeability tensor components are highly related to fracture geometry and differ from each other. For the histograms of the equivalent permeability, the shapes of k x x and k y y change from a power law-like distribution to a lognormal-like distribution when the fracture length and the number of fractures increase. For the off-diagonal component k x y , it is a normal-like distribution and its range expands when the fracture length and the number of fractures increase. The mean of diagonal equivalent permeability tensor components increases linearly with the fracture density. The analysis helps in generating stochastic equivalent permeability models in fractured porous rocks and reduces uncertainties when applying equivalent fracture models.

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Comparison of Flow Solutions for Naturally Fractured Reservoirs Using Complex Analysis Methods (CAM) and Embedded Discrete Fracture Models (EDFM): Fundamental Design Differences and Improved Scaling Method

Geofluids ◽

10.1155/2020/8838540 ◽

2020 ◽

Vol 2020 ◽

pp. 1-20

Author(s):

Aaditya Khanal ◽

Ruud Weijermars

Keyword(s):

Complex Analysis ◽

Fractured Reservoirs ◽

Fluid Velocity ◽

Naturally Fractured Reservoirs ◽

Natural Fractures ◽

Flow Distortion ◽

Cubic Equation ◽

Analysis Methods ◽

Discrete Fracture ◽

Fracture Models

The present study compares flow paths in reservoirs with natural fractures, solved with Complex Analysis Methods (CAM), to those solved with Embedded Discrete Fracture Models (EDFM). One aim is to define scaling rules for the strength (flux) of the discrete natural fractures used in CAM models, which was previously theoretically defined based on the expected flow distortion. A major hurdle for quantitative benchmarks of CAM with EDFM results is that each of the two methods accounts for natural fractures with different assumptions and input parameters. For example, EDFM scales the permeability of the natural fractures based on a cubic equation, while CAM uses a flux strength. The results from CAM and EDFM are used to scale the flux strength of the natural fractures and improve the equivalent permeability contrast estimation for CAM. The permeability contrast for CAM is calculated from the ratio of the enhanced velocity inside natural fractures to the unperturbed matrix fluid velocity. A significant advantage of flow and pressure models based on CAM is the high resolution without complex gridding. Particle tracking results are presented for fractures with different hydraulic conductivity ranging from highly permeable to impervious.

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Discrete-Fracture Modeling of Thermal-Hydrological Processes at Yucca Mountain and the Llnl G-Tunnel Heater Test

MRS Proceedings ◽

10.1557/proc-412-747 ◽

1995 ◽

Vol 412 ◽

Author(s):

John J. Nitao ◽

Thomas A. Buscheck

Keyword(s):

Test Site ◽

Yucca Mountain ◽

Fracture Flow ◽

Transport Code ◽

Fracture Modeling ◽

Discrete Fracture ◽

The Matrix ◽

Fracture Models ◽

Equivalent Continuum

AbstractAn in situ heater test was performed at G-Tunnel, Nevada Nuclear Test Site, to investigate the thermal-hydrological response of unsaturated, fractured volcanic tuff under conditions similar to those at Yucca Mountain. The NUFT flow and transport code was used to model the test using discrete-fracture and equivalent-continuum approaches. Nonequilibrium fracture flow and thermal buoyant gas-phase convection were found to be the likely causes for observed lack of condensate imbibition into the matrix. The potential repository at Yucca Mountain was also modeled. Disequilibrium fracture flow is predicted to occur for less than a hundred years after emplacement followed by a period of fracture-matrix equilibrium, during which the equivalent-continuum and discrete-fracture models give almost identical results.

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Integrating discrete fracture network models and pressure transient data for testing conceptual fracture models of the Valhall chalk reservoir, Norwegian North Sea

Geological Society London Special Publications ◽

10.1144/gsl.sp.2007.270.01.13 ◽

2007 ◽

Vol 270 (1) ◽

pp. 193-204 ◽

Cited By ~ 5

Author(s):

S. Rogers ◽

C. Enachescu ◽

R. Trice ◽

K. Buer

Keyword(s):

North Sea ◽

Network Models ◽

Fracture Network ◽

Discrete Fracture Network ◽

Pressure Transient ◽

Discrete Fracture ◽

Fracture Models ◽

Transient Data

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Numerical Simulation of a Horizontal Well With Multi-Stage Oval Hydraulic Fractures in Tight Oil Reservoir Based on an Embedded Discrete Fracture Model

Frontiers in Energy Research ◽

10.3389/fenrg.2020.601107 ◽

2020 ◽

Vol 8 ◽

Author(s):

Zhi-dong Yang ◽

Yong Wang ◽

Xu-yang Zhang ◽

Ming Qin ◽

Shao-wen Su ◽

...

Keyword(s):

Oil Reservoirs ◽

Hydraulic Fractures ◽

Tight Oil ◽

Fine Grid ◽

Hole Pressure ◽

Bottom Hole Pressure ◽

Bottom Hole ◽

Discrete Fracture ◽

Fracture Models ◽

Tight Oil Reservoirs

Tight oil is a kind of unconventional oil and gas resource with great development potential. Due to the unconventional characteristics of low porosity and low permeability in tight oil reservoirs, single wells generally have no natural productivity, and industrial development is usually conducted in combination with horizontal wells and hydraulic fracturing techniques. To capture the flow behavior affected by fractures with complex geometry and interaction, we adopted embedded discrete fracture models (EDFMs) to simulate the development of fractured reservoirs. Compared with the traditional discrete fracture models (DFMs), the embedded discrete fracture models (EDFMs) can not only accurately represent the fracture geometry but also do not generate a large number of refine grids around fractures and intersections of fractures, which shows the high computational efficiency. To be more consistent with the real characteristic of the reservoir and reflect the advantage of EDFMs on modeling complex fractures, in this work, the hydraulic fractures are set as oval shape, and we adopted 3-dimensional oil–gas two-phase model considering capillary forces and gravity effects. We developed an EDFM simulator, which is verified by using the fine grid method (FGM). Finally, we simulated and studied the development of tight oil without and with random natural fractures (NFs). In our simulation, the pressure varies widely from the beginning to the end of the development. In real situation, tight oil reservoirs have high initial pressure and adopt step-down bottom hole pressure development strategy where the bottom hole pressure of the last stage is below the bubble point pressure and the free gas appears in the reservoir. Modeling studies indicate that the geometry of fracture has a great influence on the pressure and saturation profiles in the area near the fractures, and dissolved gas flooding contributes to the development of tight oil, and NFs can significantly improve production, while the effect of the stress sensitivity coefficient of NFs on production is more significant in the later stage of production with lower reservoir pressure.

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