A workflow for processing mono‐channel Chirp and Boomer surveys

Abstract

Acquiring seismic data with multichannel, multiple‐streamer and even multi‐componentsystems at sea provides excellent images of the Earth. However, the cost and complexity of operations prevent their use in busy areas such as ports or in sensitive environments such as lagoons. In the latter cases, mono‐channel Chirp or Boomer systems are the most viable instruments for marine surveys. The lack of multiple offsets prevents the use of standard tools for amplitude‐versus‐offset and velocity analysis, which are necessary for the lithological characterization of rocks, especially for the shallow sediments in offshore engineering. In this paper, we present a few recent techniques that exploit the traveltime and amplitude of multiple reflections to compensate for the offset limitation, including a new algorithm for the joint tomographic inversion of direct arrivals, primaries and multiples. We have developed a cost‐effective workflow for mono‐channel surveys based on a data‐driven, physically consistent philosophy that attempts to approximately extract lithological parameters, such as P velocity, anelastic absorption, acoustic impedance and even density. We applied the proposed workflow to a real field experiment and obtained a semi‐quantitative estimate for shallow sediments that can be used by offshore engineers.

Coupled Inversion of Amplitudes and Traveltimes of Primaries and Multiples for Monochannel Seismic Surveys

“…Other primary effects and diffractions are also visible in the deeper part. Figure 13 shows the seismic section after correcting the spherical divergence only for propagation in seawater by multiplying each sample by the function V w t, i.e., the velocity of the seawater and the sample traveltime [41]. Since we only invert the amplitudes of the reverberations in the water layer, we do not consider propagation effects, such as anelastic absorption in the sediments, which are appropriate when multiples across them are included.…”

“…An overview of its geological setting is provided by [40]. We selected 400 traces in a profile where we could interpret the events necessary for our inversion algorithm: the primary reflections from the seafloor and the base of the sediments, the first and second reverberation in the water layer and the peg-leg multiple of the sedi- Figure 13 shows the seismic section after correcting the spherical divergence only for propagation in seawater by multiplying each sample by the function Vw t, i.e., the velocity of the seawater and the sample traveltime [41]. Since we only invert the amplitudes of the reverberations in the water layer, we do not consider propagation effects, such as anelastic absorption in the sediments, which are appropriate when multiples across them are included.…”