基于高精度可视化测量手段的裂隙岩体渗流传质特性研究

Fluid flow and mass transport properties of fractured rocks are the corner stone subject for many geoscience and geo-engineering disciplines, such as geological disposal of radioactive waste (GDRW), carbon dioxide capture and sequestration (CCS), and geothermal energy development (GED). The inaccuracy in measurement and quantification of geometric characteristics of fractures is the main source of biased assessment of fluid flow and mass transport properties. In the present proposal, we first measure the geometries of fractures involved in prototype rocks by means of X-ray CT. The obtained data are then used to establish high-precision artificial single rock fracture and fractured rock samples based on 3D printing technology using transparent materials. Fluid flow tests along with tracer tests are conducted on these samples with the fluid flow and particle transport inside of fractures being visualized and measured via a PIV system. The numerical simulations of fluid flow through the tested samples are subsequently implemented to verify the testing and the numerical approaches, and to develop a modified constitutive law for fluid flow through rough fractures. Finally, parametric studies on numerical models with changing geometric properties are put forward to establish an expression that can effectively assess the permeability of fractured rocks. The primary aim of this proposal is to establish a high-precision hydraulic testing system and an effective method for estimating fluid flow and mass transport properties of fractured rocks, that could help improve the engineering design of relative projects.

研究裂隙岩体的渗流传质特性对核废料的地质储存、二氧化碳的地下封存、地热利用等与国计民生密切相关的热点课题具有重要的意义。对岩体内裂隙的几何性状测量及描述的不准确性是造成渗流传质特性评估中诸多不确定性的首要因素。针对这个问题，本项目拟采用CT扫描获取样本岩块内部裂隙的几何性状；基于3D打印技术制作单裂隙和多裂隙岩块的高精度透明模拟岩石试件，忠实的表现裂隙表面的细节几何特征；研发渗流示踪测试系统，利用PIV技术精确测量裂隙内流速的三维矢量分布和粒子运移速度及路径的分布，实现裂隙内部流体和粒子运移的可视化；以试验模型为基础建立三维数值模型，与试验结果对比分析提出修正的基础流体方程；在数值模拟中改变裂隙网络几何参数，通过对结果的回归分析提出预测裂隙岩体渗透性的公式。最终建立一套高精度裂隙岩体渗流传质试验系统和评估方法，为与裂隙岩体渗流相关的工程应用提供科学依据和有效的手段。

近年来广受瞩目的高放废物地质处置、二氧化碳地下封存、地热利用、页岩气开采等项目涉及到地下岩体中的热-水-力-化多场耦合问题，其中渗流是化学反应以及传热传质的媒介和基本载体。研究裂隙岩体的渗流传质特性对于能源开发、防灾减灾、核能安全等与国计民生密切相关的重大课题具有重要的意义。本项目针对裂隙复杂的几何特征与通过其中的渗流传质特性之间的关系，开发岩石裂隙渗流传质高精度可视化试验方法，建立裂隙应力-渗流-传质耦合特性理论计算模型，研究三维裂隙交叉口渗流传质规律，分析具有真实几何形貌特征的二维及三维裂隙网络渗流特性。通过所建立的试验测试方法、理论模型以及数值模拟，定量评价了水力耦合条件下裂隙内的渗流传质特性，建立了裂隙几何形貌特征及空腔几何特征与渗透系数及物质运移控制基本参数之间的关系；提炼代表性粗糙度指标，建立了评价三维交叉裂隙混合比等物质运移特性的评价模型，阐明了不同佩克莱数下溶液在交叉口的混合特性；在二维及三维裂隙网络中融合了剪切模块，建立了裂隙几何参数与渗透系数的定量关系，揭示了剪切过程对裂隙渗流特性的作用规律。项目建立的方法和模型阐明了裂隙复杂几何特征对其中渗流传质特性的深刻影响，既在实验室尺度上揭示了其内在机理又在现场裂隙岩体尺度上做了定量的分析，对理解和掌握裂隙岩体的渗流传质特性有积极的推动作用。