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3D reverse-time migration using the acoustic wave equation

An experience with the SEG/EAGE data set

University of Houston, Texas, U.S.

Changsoo Shin and Sangyong Suh

Seoul National University

Larry R. Lines

University of Calgary, Alberta, Canada

Soonduk Hong

KIGAM, Seoul, Korea

Corresponding author: lines@geo.ucalgary.ca

The first 20% of the full text of this article appears below.

Kirchhoff is the most commonly used 3D prestack migration algorithm because of its speed and other economic advantages, but it uses a high-frequency ray approximation to the wave equation and, therefore, has difficulties in imaging complex geologic structures where multipathing occurs (e.g., beneath rugose horizons such as faulted salt domes where traveltime calculations become difficult).

In contrast to Kirchhoff migration, reverse-time migration computes numerical solutions to the complete wave equation and, therefore, is potentially more accurate. But this technique is not popular in the industry because it is computationally intensive and expensive. However, we felt some recent developments would allow 3D reverse-time migration to be done relatively inexpensively on PC-based distributed memory clusters.

In order to examine this hypothesis, we implemented reverse-time migration on a PC cluster by using higher-order accuracy finite difference algorithms (Wu et al., 1996), an excitation time approach (Chang and McMechan, 1994), and variable grids (Mufti et al., 1996) to reduce memory and CPU time. We then used the pseudo-spectral method—following Gazdag (1981), Kosloff and Baysal (1982), and Fornberg (1987)—to further reduce CPU time and core memory requirements.

In this article, we compare our reverse-time migration images with first-arrival Kirchhoff migration images to demonstrate that 3D reverse-time migration can produce high fidelity images under the PC-based distributed memory cluster machine.

	Application to the SEG/EAGE salt model data

 
The SEG/EAGE salt model has a complicated structural nature, which is representative of salt intrusions in the Gulf of Mexico. It is a challenging standardized test for 3D prestack depth migration algorithms and thus well suited for our comparison of reverse-time migration and Kirchhoff migration (using first-arrival traveltimes). Figure 1 shows the velocity model for inline 490 or x = 9.78 km. Figures 2 and 3 show the 3D reverse-time and Kirchhoff migrations, respectively, for this line. Figure 4 shows the velocity model for crossline 360 . . . [Full Text of this Article]