Pore network model simulation (PNM) is an important method to simulate reactive transport processes in porous media and to investigate constitutive relationships between permeability and porosity that can be implemented in continuum-scale reactive-transport modeling. The existing reactive transport pore network models (rtPNMs) assume that the initially cylindrical pore throats maintain their shape and pore throat conductance is updated using a form of Hagen-Poiseuille relation. However, in the context of calcite dissolution, earlier studies have shown that during dissolution, pore throats can attain a spectrum of shapes, depending upon the imposed reactive-flow conditions (Agrawal et al., 2020). In the current study, we derived new constitutive relations for the calculation of conductance as a function of pore throat volume and shape evolution for a range of imposed flow and reaction conditions. These relations were used to build animproved new reactive pore network model (nrtPNM). Using the new model, the porosity-permeability changes were simulated and compared against the existing pore network models.

In order to validate the reactive transport pore network model, we conducted two sets of flow-through experiments on two Ketton limestone samples. Acidic solutions (pH 3.0) were injected at two Darcy velocities i.e., 7.3 × 10⁻⁴ and 1.5 × 10⁻⁴ m.s ^− 1 while performing X-ray micro-CT scanning. Experimental values of the changes in sample permeability were estimated in two independent ways: through PNM flow simulation and through Direct Numerical Simulation. Both approaches used images of the samples from the beginning and the end of experiments. Extracted pore networks, obtained from the micro-CT images of the sample from the beginning of the experiment, were used for reactive transport PNMs (rtPNM and nrtPNM).

We observed that for the experimental conditions, most of the pore throats maintained the initially prescribed cylindrical shape such that both rtPNM and nrtPNM showed a similar evolution of porosity and permeability. This was found to be in reasonable agreement with the porosity and permeability changes observed in the experiment. Next, we have applied a range of flow and reaction regimes to compare permeability evolutions between rtPNM and nrtPNM. We found that for certain dissolution regimes, neglecting the evolution of the pore throat shape in the pore network can lead to an overestimation of up to 27% in the predicted permeability values and an overestimation of over 50% in the fitted exponent for the porosity-permeability relations. In summary, this study showed that while under high flow rate conditions the rtPNM model is accurate enough, it overestimates permeability under lower flow rates.

孔隙网络模型模拟 (PNM) 是模拟多孔介质中反应输运过程和研究渗透率和孔隙度之间的本构关系的重要方法，可在连续尺度反应输运建模中实施。现有的反应输运孔隙网络模型 (rtPNM) 假设最初的圆柱形孔喉保持其形状，并且使用 Hagen-Poiseuille 关系的形式更新孔喉电导率。然而，在方解石溶解的背景下，早期的研究表明，在溶解过程中，孔喉可以形成一系列形状，具体取决于施加的反应流动条件（Agrawal 等，2020）。在目前的研究中，我们推导出了新的本构关系，用于计算作为一系列强加流动和反应条件下孔喉体积和形状演变的函数的电导率。这些关系被用来构建改进的新反应孔网络模型 (nrtPNM)。使用新模型模拟孔隙度-渗透率变化，并与现有孔隙网络模型进行比较。

为了验证反应输运孔隙网络模型，我们对两个 Ketton 石灰石样品进行了两组流通实验。酸性溶液（pH 3.0）以两种达西速度注入，即7.3 × 10 ^-4和1.5 × 10 ^-4  m。s  ^{-  1}同时执行 X 射线显微 CT 扫描。样品渗透率变化的实验值以两种独立的方式估算：通过 PNM 流动模拟和通过直接数值模拟。这两种方法都使用了实验开始和结束时的样本图像。从实验开始时从样品的微 CT 图像中获得的提取的孔隙网络用于反应性运输 PNM（rtPNM 和 nrtPNM）。

我们观察到，在实验条件下，大多数孔喉保持最初规定的圆柱形状，因此 rtPNM 和 nrtPNM 表现出相似的孔隙度和渗透率演变。发现这与实验中观察到的孔隙率和渗透率变化合理一致。接下来，我们应用了一系列流动和反应机制来比较 rtPNM 和 nrtPNM 之间的渗透率演变。我们发现，对于某些溶解状态，忽略孔隙网络中孔喉形状的演变会导致预测渗透率值高估高达 27%，孔隙度拟合指数高估超过 50%。渗透率关系。总之，这项研究表明，虽然在高流速条件下 rtPNM 模型足够准确，