Abstract:

Laboratory-scale physical simulation experiments of hydraulic fracturing make it possible to reproduce fracture initiation, propagation, and closure under controllable conditions. By representing these sequential stages in a controlled experimental environment, such experiments provide an important means of investigating the evolution of fracture geometry, the redistribution of stress associated with fracture growth, and the mechanisms governing interactions between fractures. However, conventional monitoring approaches used in physical simulation experiments rely largely on point sensors, particularly acoustic-emission transducers and strain gauges. Because the number of measuring points is limited and their spatial distribution is discrete, the resulting monitoring signals are spatially sparse and discontinuous. It is therefore difficult to continuously capture the spatiotemporal evolution of the strain field during fracture propagation or to identify the corresponding response patterns throughout the fracturing process. Distributed fiber-optic sensing provides high-density spatial sampling, continuous measurement along the sensing fiber, and real-time response. These capabilities offer a new technical route for refined monitoring and mechanism-oriented interpretation in physical simulation experiments of hydraulic fracturing. Focusing on laboratory-scale physical modeling of hydraulic fracturing, this paper systematically reviews three categories of fiber-optic sensing technology: quasi-distributed fiber Bragg grating sensing (FBG), distributed strain sensing based on optical frequency-domain reflectometry (DSS-OFDR), and distributed acoustic sensing based on optical time-domain reflectometry (DAS-OTDR). For each category, the sensing mechanism, characteristic signal responses, and principal interpretation methods are summarized. Representative studies conducted in China and abroad are further compared with respect to their experimental systems and key observational indicators, thereby clarifying how different fiber-optic techniques have been incorporated into laboratory hydraulic-fracturing experiments. At the level of experimental methodology, typical fiber-deployment approaches and experimental paradigms under different specimen materials and loading conditions are reviewed. These include embedded fiber arrangements in transparent-medium visualization experiments, where fracture development can be observed directly and compared with the measured fiber-optic responses. The review also covers fiber anchoring and bonding in cement-based rock-like specimens under true-triaxial loading, together with equivalent multiwell deployment concepts designed to represent the spatial relationships among different wells in a controlled physical model. These experimental arrangements demonstrate how fiber-optic monitoring can be adapted to different materials, loading systems, and observation objectives. With further emphasis on advances in interpretation techniques, this paper summarizes methods for characterizing fracture geometry from offset-well strain monitoring and analyzes the characteristic fiber-optic strain responses associated with fracture evolution in true-triaxial physical models. It also outlines the identification of microseismic events from fiber-optic measurements and the application of these events to monitoring the dynamic hydraulic-fracturing process. The reviewed studies show that distributed fiber-optic monitoring is progressing from the recognition of basic fracture responses toward refined characterization of fracture geometry and interpretation of dynamic fracture evolution. Future research should strengthen experimental calibration and methodological standardization, promote the joint interpretation of strain and acoustic responses, and advance the quantitative inversion of fracture parameters. These developments will provide support for the design of physical simulation experiments, the interpretation of monitoring data, and the validation of related models.

Key words: hydraulic fracturing, physical modeling experiments, distributed fiber-optic sensing, strain monitoring, microseismic monitoring

摘要：

水力压裂物理模拟实验能够在可控条件下复现裂缝起裂、扩展与闭合过程，是研究裂缝形态演化、应力重分布及裂缝相互作用机理的重要手段。然而，传统监测方法多依赖声发射、应变片等点式传感器，测点稀疏且监测信号离散，难以连续捕捉裂缝扩展过程中应变场的时空演化特征及其响应规律。分布式光纤传感技术凭借其高空间采样密度、连续测量与实时响应能力，为物理模拟实验的精细监测与机理解析提供了新的技术路径。本文面向实验室尺度水力压裂物理模拟，系统梳理准分布式光纤布拉格光栅(FBG)、基于光频域反射的分布式应变传感(DSS-OFDR)以及基于光时域反射的分布式声波传感(DAS-OTDR)的传感机理、信号特征与解释方法，并对比国内外代表性研究的实验体系与关键观测指标。在实验方法层面，总结不同试样材料与加载条件下的典型光纤布设方式与实验范式，包括透明介质可视化实验的嵌入式布设与直观观测优势，以及真三轴条件下水泥类岩试样的光纤固结与多井等效布设思路。进一步围绕解释技术进展，重点归纳基于邻井应变监测的裂缝形态刻画方法及其在真三轴物模中的光纤应变响应特征，并概述基于光纤监测的微震事件识别及其在压裂动态过程监测中的应用。研究表明，分布式光纤监测正由裂缝响应识别向裂缝形态精细表征与动态演化过程解析发展。未来应加强实验标定与方法规范化，推进应变与声学响应联合解释及裂缝参数定量反演，为物理模拟实验设计、监测数据解释与模型校核提供支撑。

关键词: 水力压裂, 物模实验, 分布式光纤传感, 应变监测, 微震监测