Alternative Seismic Methods

seismic interferometry and passive methods can be used to construct subsurface images from seismic energy generated by exploration drilling in the mines or by recording energy generated by artificial seismic sources on the surface and recorded by Geophones or fibre optic cables in the boreholes.

Interferometric Seismic Imaging

Fiber optic cables in the borehole record seismic waves generated artificially on the surface. Signal processing and interferometric imaging can generate the subsurface image near the borehole and away from it. In the below example, we successfully imaged the subsurface with interferometry method for a fraction of cost that would have been spent using conventional 2D methods. In this example, the very near surface (0-100m) is clearly identified while this part is often muted and remains a unimaged in conventional 2D methods.

There is a good match between P-wave velocity log variations and the events on interferometric image.

Advanced Seismic Methods

Seismic velocity anisotropy is an advanced topic and complex subject in the realm of exploration seismology. knowledge of velocity anisotropy (variation of velocity of seismic waves with direction) can often improve the results of seismic imaging and depth conversion particularly when dealing with shale dominated formations and stressed/fractured rocks.

This is an example of seismic wave velocity anisotropy observed in terms of Primary wave’s arrival times (dots) that are measured inside a borehole for several sources on the surface. Unless anisotropy effects are considered the complex pattern in variation of measured traveltime is impossible to model. The model is shown by the transparent surface.

Anisotropy parameters estimated in this work provide a direct clue to the direction of the stress in the region and the degree of its effect on rocks (fractures).