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Modeling and imaging marine vibrator data
Almuteri, Khalid
Almuteri, Khalid
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2023
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Abstract
Marine vibrators are an emerging alternative technology to conventional air guns in ocean-bottom seismic acquisition. They promise to deliver greater low-frequency information about the subsurface while minimizing the adverse impact on marine wildlife. However, using marine vibrators introduces challenges not found in conventional air-gun-based acquisition. Even though marine vibrators move at a much slower velocity than the acoustic wave subsurface speed, source motion introduces a noticeable offset and time-dependent frequency shift to the data. Phase distortions also occur in seismic signals and are proportional to the source velocity and moveout of seismic events. The time-varying nature of the sea surface and the long duration of the seismic sweep present an additional set of modeling, processing, and imaging challenges. A dynamic sea surface significantly affects the phase and amplitude of seismic data, posing challenges for time-lapse studies, seismic deghosting, and surface-related multiple elimination. Conventional seismic data processing assumes a horizontal sea surface for simplification. However, characterizing the sea surface state and accurately modeling seismic data under such conditions is important for investigating the implications of realistic acquisition and for proper processing and imaging workflow design.
In this thesis, I develop a numerical approach to model long-emitting non-impulsive sources in the presence of a time-varying sea surface using the tensorial acoustic wave equation. I also derive analytical expressions to predict the frequency shifts in the seismic signal due to source motion (Doppler effect) and predict the seismic wavefield in homogeneous media triggered by a moving source (Green’s function), which I use to validate the developed modeling approach. Furthermore, I use the developed tools to account for the source motion effects in reverse-time migration, mitigating the need for pre-processing steps to remove such effects from the seismic data. I present numerical examples that demonstrate the accuracy, stability, and robustness of the tensorial formulation of the acoustic wave equation in modeling and imaging marine vibrator data, even for typically unincorporated high source velocities in field data acquisition.
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