## 5 Forward Simulation Results of Different Salt Cavity Shapes
### Influence of Sediment Height Inside Cavity  
According to the analysis of sonar measurement of the old cavity shape and drilling trajectory, there is a significant difference in the height of the insoluble residue in the salt cavity, as indicated in Table 2. These height differences are observed across different regions and even at different well locations in the same region. The composition of salt rock in saline strata varies among different salt mines, leading to differences in the height of the residue formed by the sedimentation and accumulation of insoluble matter during the brine production process. Additionally, in the same region, factors such as production methods and time can also impact the accumulation height of the residue within the cavity. Consequently, investigating the seismic reflection characteristics of varying residue heights is crucial for gaining insights into the morphology of salt cavities.  
Figure 19 shows the seismic record profile of variable density with different residual height. Notably, the reflection feature of the cavity's top surface remains consistent, featuring a strong wave trough that is unaffected by the sediment height. The entire cavity presents a \"ring-shaped\" reflection pattern, with scattered, weak reflections within its confines. As the residue height increases, the lower boundary of this \"ring-shaped\" waveform shifts gradually upward. When the residue height in the cavity reaches 90% of the cavity's total height, the lower boundary of the circular reflection wave vanishes.  
Figure 17: Seismic record profiles of variable density at different cavity height. The blue dashed line is employed to enhance the visualization of the relative positions of the reflected waveforms originating from the horizontal channels across the various models.  
Figure 18: Congruent diagrams of waveform seismic record profiles and cavity models with different cavity height. The blue dashed line is employed to enhance the visualization of the relative positions of the reflected waveforms originating from the horizontal channels across the various models.  
Figure 20 shows the superposition of seismic records' waveforms and salt cavern models with different residue heights. The distinct reflection feature--a strong trough at the cavity top and the \"one valley, one peak\" pattern of the connecting channel--remains consistent regardless of the sediment height. Apparently, the reflection characteristics of the residue's top surface in the cavity undergo significant changes. As the residue height increases, the downward shift of the reflection peak on the residue's top surface gradually diminishes, as depicted in Figure 21. Meanwhile, the bottom of the salt cavity continues to display chaotic reflection characteristics. Additionally, regardless of how the sediment height changes, the top surface of the residue always remains in the upper half of the circular waveform of the cavity.  
Figure 21: Relationship between sediment height inside cavity and downward shift of its reflection peak.  
Figure 19: Seismic record profiles of variable density at different sediment height.