The large-scale 3D seismic survey acquired in the first quarter of 2014 proved to be of great importance for characterisation of the SW Hub Project; mapping the main structures and key geological interfaces.
However, small to medium shallow structures were less clearly imaged in this survey, as the recording geometry was adjusted for the regional investigations and greater depths, rather than high resolution and shallower character of the formations.
A high-resolution 3D survey was undertaken to investigate whether the imaging of the shallow structures could be improved. The survey was centred at the Harvey-4 well. The principle objective was to image the complexity of the shallow structures in 3D. Close to 1600 seismic source positions were acquired over 5 days. Seismic receivers utilised single and 3-component geophones arranged into an odd-even receiver line pattern.
Preserved amplitude processing and pre-stack imaging proved to be a very effective processing approach for structural analysis. The same data can be used in the near future for more qualitative studies involving acoustic inversion and AVO studies after calibration to the Harvey-4 well logs. The Nested 3D data cube was inserted into the large, regional scale Harvey 3D survey (see images).
A comparative analysis showed the following:
- Several faults are seen in the Nested 3D data, which were not previously identifiable in the regional 3D cube. This includes faults at different scales.
- All discontinuities (large and small) are of a much higher fidelity in the Nested 3D survey.
- Some faults appear to propagate near to the surface but are of a small-scale throw.
- Faulting in the area is highly complex.
- The Harvey-4 well appears to have drilled through a fault of a large throw (several tens of metres).
- These results demonstrate that high-resolution surveys are important for imaging the top 1,000m of sediments. The Nested 3D survey produced higher fidelity imaging of faults down to at least 1,500m in comparison to the regional 3D data.
- New seismic images allow for the interpretation of faults, previously unidentified in the regional 3D survey.
- Even some deep, large-scale faults are better imaged with the new high-resolution survey than the regional survey.
- The fault complexity revealed by the new data suggests that a much higher data density and resolution is required in order to accurately analyse and characterise the SW Hub reservoir.
- This data can enhance the static models to more accurately characterise the layering of the formations.