Multi-hole joint acquisition of a 3D-RVSP in a karst area: Case study in the Wulunshan Coal Field, China

Abstract

Conventional surface seismic exploration in areas with complex surfaces such as karst landforms has been faced with the problem of poor excitation and reception conditions. RVSP (reverse vertical seismic profile) seismic exploration adopts a geometry in which the sources are downhole and receivers are on the ground which can reduce the influence of complex surfaces on seismic wave propagation (to some extent). Through numerical simulations and real data analysis, it was noted that in areas with complex surfaces and large numbers of underground karst caves, seismic waves generated in shallow boreholes are easily affected by various surface and multiple waves as well as by scattering from karst bodies. Therefore, the quality of the reflected seismic data is extremely low. Also, it is difficult to improve the signal to noise ratio (SNR) with conventional noise filtering methods. However, when the source depth is increased, the quality of the reflected waves can be improved. This is exactly what the RVSP method accomplishes. Besides, for the RVSP method, due to its particular geometry, the apparent velocities of the reflected waves and most interference waves are quite different, which can help to filter most noise to further improve the SNR of the reflected signals. In this study, a 3D-RVSP exploration study using 8-hole joint acquisition was conducted in a typical karst landform. The results show that the 3D-RVSP method can obtain higher quality seismic data for complex surface conditions that have large numbers of underground karst caves. Furthermore, multi-hole joint acquisition for 3D-RVSP has higher data collection efficiency and better uniformity of underground coverage. Therefore, in this study, 38 faults were accurately revealed and at high resolution based on the 3D-RVSP imaging results.