An important tool in mapping the geology deep in the sub-surface is seismic reflection. This non-invasive technique enables us to obtain an image of the sub-surface structure and stratigraphy to determine the potential for trapping of hydrocarbons in an area.
Seismic reflection surveys use an energy source at the surface (a small explosive charge in a shallow borehole or a vibrator truck) to generate a low-level seismic signal which penetrates deep into the earth. These seismic waves are reflected from different rock layers and a series of sensitive recorders called geophones record these reflections at the surface.
Seismic surveys can be recorded along a single profile for example along a road (2D seismic) or cover a larger surface area to generate a volume of information (3D seismic).
The information in seismic surveys is recorded by reference to the time a sound wave takes to be reflected back to the surface and must be converted into depth using well and rock velocity information.