Background of Seismic Processing

Seismic data takes a long journey from being sound vibrations in the ground to meaningful information on a computer screen in a conference room. The process involves a large amount of equipment, skilled people and time. It's a delicate process, requiring sound judgment and attention to the smallest details.

The first step involves generating sound waves in the ground and listening for their return as they bounce back from various rock layers below the surface - comparable to what you could see in a two dimensional water ripple. The returning waves contain information in various forms -- frequencies, phase relationships, amplitudes, and more -- but even after they are recorded, the waves must be processed before any real meaning can be extracted. For example, geoscientists must calculate the depth location of each reflected wave.  This, of course, requires an understanding of how the strength and speed of the wave is impacted as it propagates through the unique rocks and subsurface features it encounters.

The output of such calculations is called pre-stack data.

Once the initial waves are processed, all the different waves that reflected from a common depth point (CDP) are combined into a single wave. This process is called stacking, and is usually accomplished by averaging the wave information together for a single Common Depth Point. The end result provides a one-to-one relationship between individual waves and surface locations.

The output of stacking the data is called post-stack data. This is where most oil people begin their analysis.

Unprocessed seismic waves contain information that does not immediately compute in the human mind--it may not have that familiar look, like "sliced bread" (for example, would you have guessed that this is what you are looking at in the picture to your left?).   In addition, there's SO MUCH data that our minds can't absorb and process it without some help. So the system must process a great deal of data to begin to create relationships that make sense to humans.

Next: Overcoming Challenges in Seismic Interpretation