## 4 Results
### The Porosity
#### 4.1.1 The Influence of Hydrochemistry  
When \(k_{w}\) is 2, T is 75 \({}^{\circ}\)C, the distribution of porosity at different pH values and time is shown in Figures 4 and 5. In order to observe and analyze the porosity distribution conveniently, the porosity values at 692 points at each time step are sorted according to the ascending order in Figure 5. In these figures, the porosity values at most points increase with increasing time and pH value. Meanwhile, the difference between the minimum and maximum values of porosity at the 692 points increases with increasing time, which indicates that the heterogeneity of porosity increases with increasing time. \begin{table}
\begin{tabular}{c c} \hline
**Parameter Name** & **Value** \\ \hline Confining pressure & 5 MPa \\ Axial pressure & 20 MPa \\ Initial average porosity \(\overline{\phi}_{in}\) & 0.11 \\ Solid density \(\rho_{s}\) & 2660 m\({}^{3}\)/kg \\ Bulk modulus & \(9.896\times 10^{9}\) N/m\({}^{2}\) \\ Shear modulus & \(8.051\times 10^{9}\) N/m\({}^{2}\) \\ Fluid density \(\rho_{f}\) & 1000 m\({}^{3}\)/kg \\ Dynamic viscosity \(\mu\) & \(1\times 10^{-3}\) Pa-s \\ Thermal conductivity of fluid \(k_{f}\) & 0.6 W/(m-K) \\ Heat capacity of fluid \(c_{f}\) & \(4.2\times 10^{3}\) J/(kg-K) \\ Thermal conductivity of solid matrix \(k_{s}\) & 2.8 W/(m-K) \\ Heat capacity of solid matrix \(c_{s}\) & \(9.21\times 10^{2}\) J/(kg-K) \\ Permeability parameter \(k_{c}\) & \(1.1\times 10^{-10}\) m\({}^{2}\) \\ Porosity diffusivity coefficient \(\lambda\) & \(1\times 10^{-11}\) m\({}^{2}\)/s \\ Scale parameter \(\lambda_{w}\) & 0.12 \\ \hline \end{tabular}
\end{table} 
Table 1: The model parameters. The average and variance of porosity and fluid velocity at the 692 points are shown in Figure 6. Figure 6a-c show the average porosity and porosity variance at different shape parameters. The variance change can reflect the porosity heterogeneity change. In this figure, the curves between average porosity and time are approximately straight lines, and their slopes increase with the increase of the pH value, which indicates that the increase of the pH value can increase the porosity growth rate. At different shape parameters, the curves have little change, which indicates that the heterogeneity of the initial porosity has little influence on porosity change. The porosity variance firstly experiences a slight then rapid increase, and approximately shows exponential growth with increasing time. Therefore, the rock heterogeneity increases with increasing time. In addition, by increasing the shape parameter, the increased range of the variance decreases. Specifically, after \(5\times 10^{6}\) s, when the pH value was 6.6, and \(k_{w}\) was 2, the variance increased from \(2.09\times 10^{-4}\) to \(3.49\times 10^{-3}\) (increased by \(3.28\times 10^{-3}\)); when \(k_{w}\) was 5, the variance increased from \(4.12\times 10^{-5}\) to \(1.35\times 10^{-3}\) (increased by \(1.31\times 10^{-3}\)); when \(k_{w}\) was 8, the variance increased from \(1.77\times 10^{-5}\) to \(4.37\times 10^{-4}\) (increased by \(4.20\times 10^{-4}\)). The porosity variance values at different pH values are listed in Table 2. As illustrated in this table, the pH value has little influence on the porosity variance change, which indicates that the pH value has little influence on rock heterogeneity change. Figure 5: The porosity values at 692 points at different times and pH values (\(k_{w}\) = 2): (a) pH = 6.6; (b) pH = 6; (c) pH = 5; (d) pH = 4. Figure 6: The average porosity and porosity variance: (**a**) \(k_{w}\) = 2; (**b**) \(k_{w}\) = 5; (**c**) \(k_{w}\) = 8; (**d**) pH = 6.6; (**e**) pH = 6; (**f**) pH = 5; (**g**) \(k_{w}\) = 2; (**h**) \(k_{w}\) = 5; (**i**) \(k_{w}\) = 8; (**j**) pH = 6.6; (**k**) pH = 6; (**l**) pH = 5. The porosity heterogeneity growth indicates that the porosity has an evolution of the polarity between 0 and 1. In order to better observe the cracks, it is assumed that the points with over 0.5 of porosity value can form the cracks.