GeoDFN - A Flexible, Open-Source Software for Generating Geologically Consistent Discrete Fracture Networks

GeoDFN is an open-source software that provides comprehensive control over fracture properties and allows us to explore how a broad range of geological uncertainties impact the geometry and connectivity of fracture networks. GeoDFN employs a hybrid approach, combining the advantages of mechanical and statistical methods in generating DFNs, which ensures geological consistency in fracture placement while maintaining computational efficiency. At the core of this hybrid approach is the consideration of stress shadow, as buffer zone around fractures, which impose a minimum spacing between fractures and prevent them from being placed in geologically unrealistic locations. Considering stress shadow also imposes a natural limit on the maximum fracture intensity of the network, reflecting the network saturation observed in real geological formations. Various models for calculating fracture apertures are provided in GeoDFN, including models that account for external stress conditions, such as the Barton-Bandis model. This capability enables detailed analysis of how fracture apertures influence fluid flow and network permeability under different geological conditions.<br>GeoDFN can be linked to any flow simulator capable of modeling fluid flow in fractured geological formations, providing a versatile tool for subsurface flow analysis. Here, we demonstrate its integration with the MATLAB Reservoir Simulation Toolbox (MRST), an open-source simulator widely used for modeling flow and transport processes. The integration with MRST enables users to easily import generated DFNs and conduct a variety of simulations, including single-phase and multiphase flow, heat transfer, and solute transport. By utilizing MRST’s Embedded Discrete Fracture Model (EDFM) approach, the complex interactions between fractures and the surrounding rock matrix are accurately represented. This connection facilitates the evaluation of how different uncertainties in fracture properties affect subsurface flow behavior, making it a powerful tool for uncertainty quantification and sensitivity analysis in diverse geological settings.<br>

GeoDFN是一款开源软件，可对裂缝属性实现全方位调控，助力研究者探究各类地质不确定性因素如何影响裂缝网络的几何形态与连通性。GeoDFN采用混合建模思路，融合了力学方法与统计方法在生成离散裂缝网络（DFN，Discrete Fracture Network）时的优势，既能保障裂缝布设的地质合理性，又能兼顾计算效率。该混合方法的核心在于考量应力阴影效应：将其作为裂缝周边的缓冲区域，以此限定裂缝间的最小间距，避免裂缝被布置在不符合地质实际的位置。同时，应力阴影效应还会自然限定裂缝网络的最大裂缝密度，这一特性契合真实地质构造中观测到的网络饱和现象。GeoDFN内置多种裂缝开度计算模型，其中包含考虑外部应力条件的巴顿-班迪斯（Barton-Bandis）模型。借助该功能，可开展精细化分析，探究不同地质条件下裂缝开度如何影响流体运移与网络渗透率。<br>GeoDFN可与任意可模拟裂缝性地质构造内流体运移的流动模拟器对接，为地下流体分析提供通用工具。本文以其与MATLAB油藏模拟工具箱（MRST，MATLAB Reservoir Simulation Toolbox）的集成为例展开演示——MRST是一款广泛应用于流动与输运过程模拟的开源模拟器。与MRST的集成可使用户便捷导入生成的离散裂缝网络，并开展多类模拟工作，包括单相流、多相流、传热以及溶质运移等。通过利用MRST的嵌入式离散裂缝模型（EDFM，Embedded Discrete Fracture Model）方法，能够精准表征裂缝与周围岩石基质间的复杂相互作用。该集成方案有助于评估裂缝属性的各类不确定性如何影响地下流体运移特性，使其成为不同地质场景下不确定性量化与敏感性分析的强有力工具。