Enhanced seismic imaging
The effective management of exploration, development, and production assets requires an accurate picture of the subsurface structures and properties. Seismic imaging is the process that positions reflections in their proper locations with their proper amplitudes and phase. Historically, imaging includes a number of processes that include signal enhancement, deconvolution, statics, velocity analysis and velocity model building, migration, and inversion. Although seismic imaging technology has seen significant advances in recent years, there remain challenges, especially in geological environments such as sub-salt, overthrust, and carbonate settings, or onshore in rugged terrains. In order to meet these challenges, researchers have focused on more accurate wave-equation-based migration algorithms such as reverse time migration (RTM). Because these advanced migration algorithms require more detailed and accurate velocity models, another area of active research is to improve velocity models that include anisotropy using tomography and full waveform inversion.
Most of these recent developments in seismic imaging come at a significant computing cost. In addition, most applications of seismic imaging are focused on specular reflections associated with continuous surfaces. Current imaging methods generally ignore discontinuous seismic events such as diffractions, which are associated with faults, fractures, terminations, and other small-scale subsurface features. Diffraction imaging can resolve these features below the typical seismic wavelength. This is particularly useful for geologically complex carbonate systems. Carbonates can be strongly heterogeneous, making them difficult to image using conventional methods.
Conventional seismic imaging also relies on data acquired using active sources and large surface receiver arrays. However, there are places where the use of active sources is not possible. For these areas, one can produce subsurface structural images by recording ambient noise like that arising from drilling. In other areas, large surface arrays may not be practical. Borehole seismic methods such as offset vertical seismic profiles, walk-away VSP, and 3D VSP provide alternatives to, or are complementary with surface seismic data. Although borehole imaging is more targeted compared to surface seismic, the data are often of much higher resolution. In addition, the acquisition of borehole seismic data is facilitated by the development of distributed acoustic sensing (DAS), which turns standard fibre-optic cable into a continuous seismic receiver.
To support the application of enhanced seismic imaging, CRGC is working in the following areas:
- imaging methods that do not require separate velocity analysis
- using diffractions for imaging and migration steering
- passive seismic and seismic interferometry
- modelling and processing of ghost waves
- full waveform inversion of vertical seismic profiles
- seismic anisotropy from VSP and surface seismic data
- distributed acoustic sensing field applications