An Advanced Discrete Fracture Methodology for Fast, Robust, and Accurate Simulation of Energy Production From Complex Fracture Networks. Issue 5 (27th April 2022)

• Record Type: Journal Article
• Authors: de Hoop, S.; Voskov, D. V.; Bertotti, G.; Barnhoorn, A.
• Is Part Of: Water resources research. Volume 58:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-04-27
• Subjects: efficient discrete fracture methodology -- complex fracture networks -- geothermal energy -- two‐phase flow -- uncertainty -- topology; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2021WR030743
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Fracture networks are abundant in subsurface applications (e.g., geothermal energy production, CO2 sequestration). Fractured reservoirs often have a very complex structure, making modeling flow and transport in such networks slow and unstable. Consequently, this limits our ability to perform uncertainty quantification and increases development costs and environmental risks. This study provides an advanced methodology for simulation based on Discrete Fracture Model approach. The preprocessing framework results in a fully conformal, uniformly distributed grid for realistic 2D fracture networks at a required level of precision. The simplified geometry and topology of the resulting network are compared with input (i.e., unchanged) data to evaluate the preprocessing influence. The resulting mesh‐related parameters, such as volume distributions and orthogonality of control volume connections, are analyzed. Furthermore, changes in fluid‐flow response related to preprocessing are evaluated using a high‐enthalpy two‐phase flow geothermal simulator. The simplified topology directly improves meshing results and, consequently, the accuracy and efficiency of numerical simulation. The main novelty of this work is the introduction of an automatic preprocessing framework allowing us to simplify the fracture network down to required level of complexity and addition of a fracture aperture correction capable of handling heterogeneous aperture distributions, low connectivity fracture networks, and sealing fractures. The graph‐based framework is fully open‐source and explicitly resolves small‐angle intersections within the fracture network. A rigorous analysis of changes in the static and dynamic impact of the preprocessing algorithm demonstrates that explicit fracture representation can be computationally efficient, enabling their use in large‐scale uncertainty quantification studies. Plain Language Summary: Fractured rocks occur naturally and are abundant in the Earth's subsurface, especially in rocks that host a variety of resources, from geothermal energy to clean water. Modeling fluid flow in such systems is complex and time‐consuming, increasing environmental and economic risks. We attempt to tackle this problem by introducing an advanced modeling technique that simplifies the fractures' representation while maintaining the main characteristics. The method's performance is analyzed based on changes in the geometry of the fractures and fluid‐flow patterns. The framework manages to significantly speed up the required time for fluid flow calculations while remaining close to the high‐fidelity solution (i.e., solution of unchanged fracture configuration). Because most of the parameters in subsurface‐related energy applications are uncertain, many simulations have to be carried out to quantify these uncertainties. Since our framework reduces the computational time, more simulations could be executed, reducing the risks associated with the development of subsurface energy resources. Key Points: An open‐source preprocessing tool that creates a fully conformal uniform grid for realistic fracture network with variable apertures The methodology allows us to use accurate Discrete Fracture Model (DFM) models with similar computational complexity as the embedded DFM approach The simplified DFM representations of fracture networks still capture characteristics and flow response of real complex networks