Seismic waves, the same type of waves used to study earthquakes, are also used to explore deep underground reservoirs of oil and natural gas.

Seismic waves–the same tool used to study earthquakes — are frequently used to search for oil and natural gas deep below Earth’s surface. These waves of energy move through the Earth, just as sound waves move through the air. In oil and gas exploration, seismic waves are sent deep into the Earth and allowed to bounce back. Geophysicists record the waves to learn about oil and gas reservoirs located beneath Earth’s surface. Bob Hardage of the University of Texas Bureau of Economic Geology is an expert in the use of this technology for oil and gas exploration. He spoke to EarthSky’s Mike Brennan.

Two vibroseis sources work in unison to form a seismic source array across a co2 sequestration site.

Q: How are seismic technologies used in finding oil and gas today?

A: What we use in exploring Earth’s energy resources is called reflection seismology. When you use seismic waves in the study of earthquakes, the earthquakes are the source of energy, that is, the source of the waves. But, in using reflection seismic technologies for oil and gas exploration, we have to deploy some kind of an acceptable energy source on the surface of the Earth and then distribute an appropriate number of seismic sensors across the Earth’s surface that will record the waves that are reflected back.

Q: So you’re sending seismic waves down into the Earth, they bounce back, and then you’ve got sensors across the surface of Earth that pick up those reflections?

A: Yes. That is exactly what is done. There are a variety of energy sources used. The most common one that’s used onshore is called vibroseis. They’re very large, heavy vehicles that weigh 60,000 to 70,000 pounds. They apply a base plate to the Earth, and they have a hydraulic system integrated into the vehicle that vibrates that base plate over a predetermined frequency range. So the vibroseis — which is what we would call the source station– becomes the energy source of the seismic waves.

The wavefield generated at the source station radiates away from that point as a three-dimensional wave. It goes down and reflects back. The reflected wavefield from each rock interface that is encountered in the propagation of this down-going wavefield is then recorded at the Earth’s surface by sensors, which we call geophones. They’re distributed in specific geometries on the surface, above the area of interest. We use those sensor responses to image the interior of the Earth, in places where we’re interested in getting a very detailed understanding of geology.

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