Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Earth and Planetary Science, University of California , Berkeley, Berkeley, California 94720, United States.
Environ Sci Technol. 2016 Jul 19;50(14):7564-71. doi: 10.1021/acs.est.6b02184. Epub 2016 Jul 8.
Understanding fracture alteration resulting from geochemical reactions is critical in predicting fluid migration in the subsurface and is relevant to multiple environmental challenges. Here, we present a novel 2.5D continuum reactive transport model that captures and predicts the spatial pattern of fracture aperture change and the development of an altered layer in the near-fracture region. The model considers permeability heterogeneity in the fracture plane and updates fracture apertures and flow fields based on local reactions. It tracks the reaction front of each mineral phase and calculates the thickness of the altered layer. Given this treatment, the model is able to account for the diffusion limitation on reaction rates associated with the altered layer. The model results are in good agreement with an experimental study in which a CO2-acidified brine was injected into a fracture in the Duperow Dolomite, causing dissolution of calcite and dolomite that result in the formation of a preferential flow channel and an altered layer. With an effective diffusion coefficient consistent with the experimentally observed porosity of the altered layer, the model captures the progressive decrease in the dissolution rate of the fast-reacting mineral in the altered layer.
理解地球化学反应引起的断裂变化对于预测地下流体迁移至关重要，这与多个环境挑战相关。在这里，我们提出了一种新的 2.5D 连续反应传输模型，该模型能够捕捉和预测近断裂区断裂开度变化和变质层发育的空间模式。该模型考虑了断裂面中的渗透率非均质性，并根据局部反应更新断裂开度和流场。它跟踪每个矿物相的反应前沿，并计算变质层的厚度。通过这种处理，模型能够解释与变质层相关的反应速率的扩散限制。模型结果与 Duperow 白云岩中注入 CO2 酸化卤水的实验研究吻合较好，导致方解石和白云石溶解，形成优先流通道和变质层。利用与实验观察到的变质层孔隙度一致的有效扩散系数，模型捕捉到了变质层中快速反应矿物的溶解速率的逐渐降低。
