GCSP Ray Tracing Dynamic Corrections - Coalfield Example, Western China

In the mountainous area of the western China, coalfield seismic exploration makes the static corrections issue caused by complex near surface to be even more prominent. Compared with oil and gas seismic exploration, the depth of coal seam is often much shallower, even less than 100 m. In this case, the raypaths will not be vertical and static shifting will introduce much more errors if we adopt the surface-consistent assumption. In order to solve the serious static corrections, we develop an effective ray tracing dynamic corrections based on ghost common-source points (GCSP) gather, which differ form different reflection times, source-to-receiver offsets and azimuths. After dynamic corrections applied, a non zero-offset CDP gather is converted to a zero-offset CDP gather, and then stack can be implemented without NMO corrections. This avoids velocity analysis without effective velocity semblance contour plots when seismic data with low signal-to-noise ratio in complex near-surface areas. In addition, NMO stretching of coal seam reflection is usually serious since the depth of coal seam is shallow. Luckily, dynamic corrections can avoid to mute distortion of NMO stretching. Application of the method to real data shows the near-surface anomaly is eliminated effectively and the reflector continuity is enhanced greatly.