Seismic Basics

• Sound waves are generated at the surface of the ground or water using sources such as dynamite, air cannons (in water), and heavy-duty vibrators. The sound waves reflect off the subsurface layers and return to an array of receivers. The data is combined and processed to create an approximate image of the layers of rock below the surface.
  
  

3D Seismic

• The first seismic surveys were two-dimensional records, recorded along a single line of shot points. As technology improved, three-dimensional seismic surveys have become more common. A 3D survey is an array of many closely-spaced 2D lines.
  
  

4D Seismic

• In 4D seismic, the fourth dimension is time. This 4D seismic is the comparison of 3D seismic surveys taken at different points in time over the same area, typically a producing field. If processed correctly, such surveys can be compared to evaluate the effects of hydrocarbon production and injection of fluids in secondary recovery operations.