Graph-based flow and transport model and dataset for fractured granite core

Fractures are a primary feature controlling flow, transport, and coupled processes in geologic systems. To date, experimental image-based observations of these processes have been challenging. Here, we successfully demonstrate the use of a graph-based, laboratory-validated flow and transport model for conservative solute transport in a natural fracture. Pulse-tracer experiments with a conservative radiotracer ([18F]-FDG) spanning multiple flow regimes with simultaneous positron emission tomography (PET) imaging are used to characterize transport in a two-inch fractured Sierra granite core. Model network complexity, determined by the number of nodes and edges, significantly impacts model fit to observed data. Large graphs over-describe a fracture plane and act similarly to a porous medium while small graphs oversimplify the solute transport behavior. This work provides the first validation of graph-based flow and transport models across a range of experimental conditions and sets the groundwork for upscaling to more complex and computationally efficient fracture network models.

裂隙是控制地质系统中流体流动、溶质运移及耦合过程的核心特征。迄今为止，基于成像技术开展上述过程的实验观测仍存在较大挑战。本研究成功验证了一款基于图结构、经实验室验证的流动与运移模型在天然裂隙内保守溶质运移模拟中的应用。研究采用搭载保守性放射性示踪剂[18F]-氟代脱氧葡萄糖（[18F]-FDG）的脉冲示踪实验，结合同步正电子发射断层扫描（positron emission tomography, PET）成像，涵盖多种流动状态，对2英寸塞拉花岗岩裂隙岩心内的溶质运移过程进行表征。模型网络的复杂度由节点与边的数量决定，其对模型拟合观测数据的效果存在显著影响：规模过大的图结构会过度刻画裂隙平面的特征，表现出与多孔介质相似的运移行为；而规模过小的图结构则会过度简化溶质运移的真实规律。本研究首次在多种实验条件下验证了基于图结构的流动与运移模型，为构建更复杂且计算效率更高的裂隙网络模型奠定了基础。