A Polarization Migration Velocity Model Building Method for Geological Prediction Ahead of the Tunnel Face

Bo Wang,Lanying Huang

doi:10.3389/feart.2022.857984

Abstract

It has been difficult to establish velocity models that use reflected seismic signals with advanced prediction ahead of the tunnel face. The accurate establishment of advanced velocity models face issues including artifacts in migration results and incorrect calculation of velocity. This study presents a polarization migration velocity model building method to solve these issues. First, the artifacts in migration interfaces were eliminated by the polarization characteristics of three-component reflected signals. Second, the optimum velocity ahead of the tunnel face was determined according to the energy stack characteristics of common interface points. Finally, the velocity model was established based on optimum velocity parameters and corresponding polarization migration interfaces using a three-dimensional and three-component numerical simulation conducted on faults with high dip and different inclinations. The results indicate that the velocity errors in the advanced velocity model were 1 and 2% for each of the two layers, and the position errors of the two interfaces were smaller than 3 and 2%. The experimental results of the Maanshan tunnel verified the effectiveness of the polarization migration velocity model building method.

Highlights

Abnormal geological structures, such as faults and fracture zones, are the principal sources of disasters (Li et al, 2017; Fan et al, 2021; Huang et al, 2021)
This study demonstrates the polarization migration velocity model building (PMVMB) method in theory and introduces the calculation principle by which Hilbert polarization migration is used to eliminate the symmetric interface artifact
We introduced a method for determining the optimum velocity based on the energy stack characteristics of common interface point (CIP) gather

Summary

INTRODUCTION

Abnormal geological structures, such as faults and fracture zones, are the principal sources of disasters (Li et al, 2017; Fan et al, 2021; Huang et al, 2021). To solve a key scientific problem for geological prediction, a reflected seismic signal should be used to build an accurate velocity model for the unexcavated area ahead of a tunnel face. The corresponding optimum migration velocity can be obtained by calculating the maximum value of stacked energy: FIGURE 3 | Calculation flowchart of the polarization migration velocity model building method for geological prediction ahead of the tunnel face. With regard to three-component reflected signals, the velocity and the position of reflection interfaces can be accurately calculated with the PMVMB method This method has a competitive edge over other velocity model building methods because it has relatively low observation system requirements. The PMVMB method automatically combines the velocity analysis and migration imaging, and the velocity value and reflection interface are completed at one time, which has better efficiency and more accurate results. The velocity model building method of S-wave is the same, and the premise is the separation of P-wave and S-wave (Liu et al, 2020)

CONCLUSION

DATA AVAILABILITY STATEMENT