Carbonate reservoir characterization using seismic diffraction imaging

Ordovician

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Figure 4. Modeled Ordovician zero-offset data: (a) conventional data; (b) separated diffraction data

We begin our experiment on the constant-density Ordovician synthetic velocity model, Figure 1, by calculating reflectivity. We transform this reflectivity to the time domain, convolve it with a 20 Hz ricker wavelet, and transform it back to the depth domain to create an idealized seismic reflectivity image. Zero-offset data is generated by performing time domain low-rank forward modeling on the idealized image (Fomel et al., 2013b), providing us with conventional zero-offset data, Figure 4a.

Data slopes are calculated using PWD, and events conforming with that slope are removed, providing the set of diffraction data shown in Figure 4b. Conventional and diffraction data are migrated using low-rank RTM with a smoothed-slowness velocity field to provide a conventional image, shown in Figure 5a, and a diffraction image, shown in Figure 5b.

To highlight the improvement in horizontal feature resolution using diffraction imaging we take two depth slices from the images, which will be interpreted and discussed in the subsequent section. The depth slices represent the average of a 20 m interval centered around the target depth. Depth slices of the conventional and diffraction images for the first depth, 0.55 km, are visible in Figures 6a and 6b. We zoom in on an interesting region of these slices featuring the karst interface and several superimposed voids to generate Figure 7.

Conventional and diffraction image slices for the second depth, 0.7 km, are shown in Figure 8. We zoom in on an area with several closely spaced voids, creating Figure 9.

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Figure 5. Low-rank RTM smoothed-slowness images for Ordovician model: (a) conventional image; (b) seismic diffraction image

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Figure 6. Ordovician depth slices from 0.55 km: (a) conventional image; (b) seismic diffraction image

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Figure 7. Zoomed Ordovician depth slices from 0.55 km: (a) conventional image; (b) seismic diffraction image

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Figure 8. Ordovician depth slices from 0.7 km: (a) conventional image; (b) seismic diffraction image

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Figure 9. Zoomed Ordovician depth slices from 0.7 km: (a) conventional image; (b) seismic diffraction image

Carbonate reservoir characterization using seismic diffraction imaging