Research in Seismic Processing and Imaging is currently ongoing in the following areas:
- Passive seismic and Seismic Interferometry
- Imaging methods that do not require separate velocity analysis
- Using diffractions for imaging and migration steering
- Modelling and processing of ghost waves
Passive seismic and Seismic Interferometry
Seismic imaging and subsurface characterisation without the use of active sources has gained importance due to the need for both monitoring microseismic events and simplified acquisition of data.
Our focus in the area of passive seismic and interferometry includes: using drilling activities as a seismic source; passive imaging of diffractors and their characterisation and separation from microseismic events; and, generating shear-wave sources at the locations of 3C geophones in VSP type experiments for imaging and anisotropy estimation.
Imaging methods that do not require separate velocity analysis
Seismic migration methods rely on a background velocity model of the subsurface.
Methods that can provide velocity models automatically along with the migrated seismic data can form an important part of the imaging and characterisation workflows.
We are developing various prestack imaging methods that result in subsurface velocity models. Currently, the focus is on time migration algorithms. The methods generally rely on the estimation of extra attributes, such as local slopes or curvatures, or use of stationary phase in a summation over the velocities.
Using diffractions for imaging and migration steering
Seismic diffractors correspond to many important subsurface features that are usually not well imaged using methods developed for reflection seismology.
Specialised methods that focus on imaging of diffractors thus enhance the resolution of the subsurface images. One of the research topics of the Discipline is imaging of the diffractors along with their seismic characterisation using their amplitude response. This approach is closely linked to improving reflection imaging in low signal to noise environments since only small parts of the diffraction hyperbolae used for summation in standard migration algorithms contain the energy from the reflection. Therefore, the inclusion of all the traces from such diffraction hyperbola may not contribute constructively to the final image.
One way of identifying the traces that do not contribute constructively to the final image is by using the amplitude/energy distribution information used in the abovementioned diffraction imaging/characterisation. We use a modified 3D Kirchhoff post-stack migration algorithm that utilises coherency attributes obtained by diffraction imaging algorithm in 3D to weight or steer the main Kirchhoff summation.
Modelling and processing of ghost waves
Reflections from the sea surface play an important role in seismic data analysis.
Temporal and spatial changes in the seismic wavelet caused by the presence of the ghost waves have to be accounted for during processing. Similar issues can also arise in development and application of surface-related multiple elimination techniques. An assumption of a flat sea surface with the reflection coefficient close to -1 has been known to be inadequate for many real-life situations.
A lot of attention has been paid to the topic of rough-sea problems in the recent time, largely because of the development of the deghosting algorithms, where the abovementioned assumption can be violated. Bóna, Egorov et al. (2015) presented a comparison of rough sea surface reflection modelling results with ultra-high resolution field seismic data acquired with deep-towed sources and receivers. The Kirchhoff approximation was used to model the sea surface response. Such a comparison is essential in establishing the validity of the modelling approaches used in data processing, such as deghosting. Deep-towed sources and receivers permit the separation of sea surface reflections from primary events.