Surface Noise for most Oil & Gas Industry Reflection Seismic Surveys is More Complex than Many Whole Earth Surface Wave Models because the Geology and Frequency Ranges are So Different

Abstract:

For the reflection seismic industry on land, source generated seismic surface noise is a main barrier to improving seismic imaging. The industry’s understanding of this noise is poor and its methods for attenuating the surface noise are often ineffective. The approach of collecting massive data redundancy to reduce noise is reaching its limits. This industry needs new approaches to do better.

To understand the noise generating processes better, we perform unique 3D acquisition tests that record 2D noise patterns over a wide frequency range. Results show that industry surface noise consists much of forward scattered and back scattered high mode Rayleigh and Love waves and guided waves. Very little energy is low order surface waves direct from the source to the receiver. This implies that 1D models of surface noise are limiting. Moreover, Rayleigh waves and Love waves may be coupled enough that they can’t be treated separately.

While the extensive academic expertise with whole earth surface waves offers significant potential to help industry, the surface noise in industry data appears to be more complex than many whole earth surface wave models. The reason for this difference is that reflection industry frequency ranges are in the 5-60Hz range and that sedimentary areas have strong heterogeneity that affect this frequency range. Review of literature suggests that the upper 100 meters in many areas of industry reflection data is a very strong wave guide that is also laterally heterogeneous. Our 3D acquisition tests support this characterization of the upper 100 meters in sedimentary areas. The model that may best suit industry geology and frequency ranges is that of a “scattering, leaky, near surface wave guide.” These strong velocity variations can provide challenges for 3D wavefield inversion (FWI) methods. We probably need to better understand the model and wave propagation effects of a scattering, leaky, near surface wave guide to significantly improve seismic reflection imaging on land.