Elastic Wave Time-reversal Source Imaging

Seismic source location is a representative research area in seismology. Wavefield can focus on source location automaticly at onset time when backpropagation seismic records using time-reversal modeling. This is called seismic source time-reversal imaging (TRI). The propagation of seismic wave in real earth is very complex, and is often approximate to elastic wave. Time-reversal imaging based on acoustic scalar wave ignore the vector feature of particle motion in elastic wave, and can only utilize waveform information of single wave mode (P or S wave). So, we carry our research on time-reversal imaging based on elastic wave.Utilizing multi-component elastic vector seismic records often generate crosstalks by different wave mode (P and S wave). If only the seismic records are separated into different wave modes, these crosstalks can be eliminated. These wave mode separating methods are based on some approximations, and is very difficult when the seismic records are complex. Separating wave mode on wavefield during forward modeling or backward extrapolation is another choose to eliminate these cross talks. The wave mode separated forward modeling plays an important role to understanding wavefield propagation and is important to seismic imaging and inversion based on elastic wave equation. This study can be divided into following parts.(1) Comparing P and S separated forward modeling methodWe compared different P and S wave separated methods during elastic wave forward modeling, and analysis their differences and similarities. We proposed methods of implementing seismic source on separated wave equation. We apply P S separated forward modeling method to analysis microseismic wavefield propagation and converted wave records in multicomponent seismic data.(2) Proposing the P and S wave interferometric correlation imaging conditionCombining PS correlation imaging condition and interferometric wavefield processing technology, we proposed the PS wave interferometric correlation imaging condition for elastic time-reversal imaging. The new imaging condition utilize the space-time character of source radiation pattern to improve the degree of wavefield focusing thus the resolution of source imaging. It also can eliminate these interferences generated by sparse geometry.(3) Elastic time-reversal imaging using signal well dataDownhole monitoring system is a regular microseismic monitoring geometry. Several multi-component receivers are deployed in monitoring well for receiving P and S wave signal from microseismic source. The traditional workflow is locate microseismic source at 2D vertical plane, then project the 2D location into 3D space using azimuthal angle. The azimuthal angle is usually determined by P wave polarization direction. In this study, We find it is feasible to do 3D elastic time-reversal imaging using signal well records. The imaging result contain source azimuthal angle information. However, the azimuthal angle is of high uncertainty, and is sensitive to the noise in data.