## 5 Forward Simulation Results of Different Salt Cavity Shapes  
### Influence of Cavity Spacing  
The distance between two wells utilized in salt mining operations is determined through a comprehensive assessment of ground morphology and the salt extraction range. During the interactive process of water injection and brine extraction, the salt rock dissolves, causing the cavities on either side to expand alternately. Consequently, the spacing between these cavities gradually diminishes. However, due to the production conditions associated with interactive water injection, the expansion of the cavities is not uniform but rather asymmetrically distributed. Wells that undergo longer water injection durations experience greater cavity expansion, resulting in varied spacing between the two cavities. To facilitate a thorough analysis of the impact of cavity spacing on seismic reflection, a model featuring symmetrically distributed cavities on both sides is employed for forward simulation research.  
Figure 12 shows the seismic record profiles of variable density at different cavity spacings. The figure reveals that the cavities on either side are distinguishable at various  
Figure 11: Seism acquisition model: an example of different spacing model.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Group** & **Factor** & **Value (m)** & **Selected Value (m)** \\ \hline
1 & Spacing & 100, 150, 200, 250, 300, 350 & 300 \\
2 & Cavern Diameter & 20, 40, 60, 80, 100 & 80 \\
3 & Cavern Height & 50, 100, 150, 200, 250, 300 & 200 \\
4 & Sediment Height & 60, 100, 140, 180 & 140 \\
5 & Channel Height & 10, 40, 90, 130 & 10 \\ \hline \end{tabular}
\end{table}
Table 3: Simulation plan for various factors.  
spacings. A prominent feature observed is the strong trough reflection at the top surface of the cavity, which is characterized by a distinct law of \"a strong wave trough sandwiched by two wave peaks\". Notably, the amplitude energy of the upper peak surpasses that of the lower peak. Within the cavity, there is a chaotic and weak reflection pattern. The overall circular nature of the cavity is evident, and as the cavity spacing increases, the annular shapes of the two cavities from the butted well gradually separates, forming an eyeglasses-like shape. As the distance between the two cavities widens beyond 200 m, the reflection characteristics of the horizontal connection channel emerge and become more discernible. This channel exhibits a medium-strong amplitude reflection feature, described as \"one valley and one peak\". This pattern provides valuable insights into the seismic behavior of the cavity and its surrounding structures.  
Figure 13 presents a superposition diagram that combines waveform data with salt cavern models with different cavern spacings. The diagram reveals that the cavity's top surface exhibits a strong trough reflection feature in the vertical direction, with the trough's position closely aligning with the cavity's top. In the horizontal direction, the trough's width is notably wider than the cavity roof and remains consistent across different cavity spacings. Inside the cavity, the sediment's top surface displays a peak reflection pattern resembling an \"upward-opening arc\", accompanied by a noticeable downward offset. This peak appears as the first one beneath the two peaks of the cavity's top surface. Additionally, the reflection characteristics of the salt cavern bottom surface are not clearly defined. Moreover, as the cavity spacing increases, the seismic reflection features of the horizontal channel become more pronounced. The channel's top surface shows a wave valley feature, with its relative position remaining consistent and unaffected by increasing cavity spacing.