Abstract

The common image gather (CIG) method enables qualitative and quantitative evaluation of the velocity model through the image. The most common such methods are offset-domain common image gather (ODCIG) and angle-domain common image gather (ADCIG). The challenge is that it requires a great deal of additional computation besides migration. We, therefore, introduce a new CIG method that has low computational cost: frequency-domain common image gather (FDCIG). FDCIG simply rearranges data using a gradient (partial image) calculated in the process of obtaining a migration image to represent it in the frequency-depth domain. We apply the FDCIG method to the layered model to show how FDCIGs behave when the velocity model is inaccurate. We also introduced the 3-D SEG/EAGE salt model to show how to apply the FDCIG method in the hybrid domain. Last, we applied 2-D real data. These sample field data also indicate that even in a complex velocity model, deviant behavior by FDCIG appears intuitively if the background velocity is inaccurate.

Highlights

  • Reverse time migration (RTM) produces a high-fidelity subsurface image from seismic data for identification of complex subsurface structures (Baysal et al, 1983; McMechan, 1983; Whitmore, 1983)

  • We briefly summarize the theory of frequencydomain RTM, a means of calculating frequencydomain common image gather (FDCIG), and related postprocessing flow

  • We examined how FDCIGs appear in the true velocity model through the first example and examined how the behavior of the FDCIGs changes when the background velocity is slightly changed

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Summary

Introduction

Reverse time migration (RTM) produces a high-fidelity subsurface image from seismic data for identification of complex subsurface structures (Baysal et al, 1983; McMechan, 1983; Whitmore, 1983). The RTM implementation in the time domain is often preferred due to its lower memory consumption than the frequency domain, and this is a critical factor in handling 3-D problems. Calculating both wavefields and imaging conditions in the frequency domain has advantages over time-domain implementation (Pratt, 1999; Wu and Alkhalifah, 2018).

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