4. Application of method in field data: Malaysian basin

The angular stack is calculated to measure the reflectivity of a particular angle, the angle stacked data are used to observe the amplitude over offset (AVO) for the Direct Hydrocarbon Indicators (DHI) and the inversion in the oil and gas industry [33, 34]. The stacking of angles also applies to the overall combination of interceptions and gradients. These angle stacks typically have a near, mid, and far angle, but an angle stack may have more than three angle stacks with a minimum of 1°. Here, for the diffraction studies, a stack of 3 angles has been realized, as shown in Figure 10. For the comparison on the near and far, the stacking is performed with two angles of 4.5 and 31.5 degrees, as shown in Figure 11. A near angle provides the best diffraction amplitude rather than a far angle stack in this study area.

As the stacking angle rises, there is a loss of amplitude in the data, as can be seen in the lower section (Figure 10). A point diffraction that can be observed in the data (2150 ms) shows the behavior of the diffraction change; the diffraction flanks are not wide in the stack of nearly staggered angles, while in the offsets, the flanks of the curves are wider. This diffraction would require a greater migration aperture to stack the energy of the top diffraction flanks (Figure 11).

Figure 10. Angle stack of three different range (a) range limited stack data with 4.5°, (b) 22.5 degrees and (c) 31.5°.

Figure 11.

Partial stack seismic: (a) near angle stack 4.5°, and (b) far angle stack 31.5°.

## 4.1 Influence of offset on diffraction imaging

Figure 12 illustrates the diffraction with different range of offset. Theoretically, the sides of the diffraction curve are influenced by the velocity and time/depth of the point diffractor [35]. However, Figure 13 shows that the diffraction also depends on the data shift because the near offset data has less diffraction response than the far-lag data. The reason for this is that the far-lag data covers more offsets and therefore recorded the wider angle data set.
