Project title: Cancellation of Surface Waves from the Active Seismic Records by Seismic Interferometry
Researcher: Dr Varun Singla
While there are seismic techniques which make use of surface waves in imaging the subsurface, there are also those where these types of waves are considered coherent noise. Important examples where the surface waves may significantly degrade the obtained images include different types of reflection seismic surveys (e.g., shallow surveys for engineering, environmental and groundwater investigations, and deep surveys for imaging hydrocarbon reservoirs). In a strongly heterogeneous medium (encountered typically in onshore surveys), the conventional methods for attenuating these waves (such as f-k "velocity" filtering) often do not give satisfactory results.
Seismic interferometry (initial conjecture by Claerbout, 1968) is a data-driven approach that gives the virtual records, i.e., inter-receiver Green’s function, by the cross-correlation of the traces recorded at two receivers, given that the receivers are completely surrounded by either impulsive or white noise sources (e.g. Wapenaar, 2004; van Manen et al., 2005, 2006; Wapenaar and Fokkema, 2006; Slob and Wapenaar, 2007). In such a (theoretical) case, the recovered Green’s functions contain the complete wavefield, including body waves, surfaces waves and the complex seismogram tail (coda) comprising multiply scattered waves. However, in exploration seismology, the sources are commonly placed at the surface and, as a consequence, the ambient noise field (generated by the field operations) and active shot gathers are dominated by surface waves (Nakata et al., 2015).
Seismic interferometry was first proposed for the surface wave removal in seismic reflection surveys by Dong, et al. (2006) and Halliday, et al. (2007). Although the theory can be considered to be well understood, the application of this method can be challenging. In addition, since the application of this methodology is generally done with confidential data, the limitations of the method are not well addressed in the literature and hence are poorly understood. This study, accordingly, served towards highlighting the limitations of the standard interferometric approaches and developing an alternative method for more effective removal of surface waves.