Figure1:Display of goaf in seismic time profile
Goaf interpretation is one of the main geological tasks in 3D seismic exploration. There are small coal kilns around the exploration area, a small number of coal pillars remain after coal seam mining, and weak reflected waves or continuous reflected waves are obtained after exploration. There are three phenomena shown in the time profile. First, the reflected waves of coal seam become weak, the frequency and occurrence of the reflection wave in phase axis at the boundary of the goaf change suddenly, and the reflected wave in phase axis inside the goaf is discontinuous and disorganized. Second, through the room and pillar mining, the reflection wave of coal seam becomes weaker in the same phase axis, with great changes in frequency and occurrence, which is significantly different from the reflection wave of surrounding non-goaf coal seam. Moreover, the reflection wave of layer under the reflection wave of coal seam is enhanced in the same phase axis, with sudden change in frequency and occurrence. From the whole section, it can be seen that the reflection wave of coal seam without goaf is stronger, while the reflection wave of overlying layer is weak. In the section with goaf, the reflection wave of coal seam is weak in the in-phase axis, while the reflection wave of the underlying overlying layer is strong in the in-phase axis, forming an obvious contrast. The third is that the coal seam is completely mined out, and there are a few residual coal pillars, so the reflection wave of the coal seam is missing in the seismic time profile.
Figure 1 shows the seismic data of 3D seismic goaf detection in a mine in northern Shaanxi. The goaf is shown to be weak or even missing in the same phase axis in the time profile. Through verification, the interpretation of 3D seismic goaf is consistent with the actual geological disclosure.
