Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
J Contam Hydrol. 2013 Nov;154:42-52. doi: 10.1016/j.jconhyd.2013.08.008. Epub 2013 Sep 6.
In this paper, we investigate the impact of chemical interactions, in the form of mineral precipitation and dissolution reactions, on tracer transport in fractured rocks. When a tracer is introduced in fractured rocks, it moves through the fracture primarily by advection and it also enters the stagnant water of the surrounding rock matrix through diffusion. Inside the porous rock matrix, the tracer chemically interacts with the solid materials of the rock, where it can precipitate depending on the local equilibrium conditions. Alternatively, it can be dissolved from the solid phase of the rock matrix into the matrix pore water, diffuse into the flowing fluids of the fracture and is advected out of it. We show that such chemical interactions between the fluid and solid phases have significant impact on tracer transport in fractured rocks. We invoke the dual-porosity conceptualization to represent the fractured rocks and develop a semi-analytical solution to describe the transient transport of tracers in interacting fluid-rock systems. To test the accuracy and stability of the semi-analytical solution, we compare it with simulation results obtained with the TOUGHREACT simulator. We observe that, in a chemically interacting system, the tracer breakthrough curve exhibits a pseudo-steady state, where the tracer concentration remains more or less constant over a finite period of time. Such a pseudo-steady condition is not observed in a non-reactive fluid-rock system. We show that the duration of the pseudo-state depends on the physical and chemical parameters of the system, and can be exploited to extract information about the fractured rock system, such as the fracture spacing and fracture-matrix interface area.
本文研究了化学相互作用（以矿物沉淀和溶解反应的形式）对裂隙岩石中示踪剂运移的影响。当示踪剂被引入裂隙岩石中时，它主要通过对流作用在裂隙中移动，同时也通过扩散作用进入周围岩石基质的停滞水中。在多孔岩石基质中，示踪剂与岩石的固体材料发生化学反应，根据局部平衡条件，示踪剂可以沉淀。或者，它可以从岩石基质的固相中溶解到基质孔隙水中，扩散到裂隙中的流动流体中，并随其被带出。我们表明，这种流体和固体相之间的化学相互作用对裂隙岩石中的示踪剂运移有重大影响。我们采用双重孔隙度概念来表示裂隙岩石，并开发半解析解来描述相互作用的流固系统中示踪剂的瞬态传输。为了测试半解析解的准确性和稳定性，我们将其与使用 TOUGHREACT 模拟器获得的模拟结果进行了比较。我们观察到，在化学相互作用系统中，示踪剂突破曲线表现出伪稳态，其中示踪剂浓度在有限的时间段内保持或多或少的恒定。在非反应性流固系统中不会观察到这种准稳态。我们表明，伪稳态的持续时间取决于系统的物理和化学参数，并可用于提取有关裂隙岩石系统的信息，例如裂隙间距和裂隙-基质界面面积。
