What Is Seismic Exploration

Oil rigs offshore use seismic exploration to find deposits for drilling.

Seismic exploration is the use of seismic waves to find natural oil and coal deposits. This technique works because sound waves travel at different speeds through different densities in the Earth’s crust. The differences in speed allows geologists to determine which layers are at which depths and drill accordingly. This can be done on or offshore, and is one of the first steps in finding viable deposits for drilling.

History

In 1855, Luigi Palmieri developed the first seismograph, but it wasn’t used for exploratory seismology until John C. Karcher and a team of scientists including Dr. D. W. Ohern, Dr. W. P. Haseman, William C. Kite and Dr. Irving Perrine, conducted the first experiments in 1921, in the areas outlying Oklahoma City. The tests confirmed that the subsurface below could contain oil. Eight years later, they were the first team to strike crude oil via reflective seismology.

Equipment

The equipment used in exploratory seismology has evolved over the years, becoming more sophisticated. Palmieri’s seismograph used mercury and electricity to detect seismic activity. Landside seismology once involved creating waves in the ground via explosives, which would then cause the earth to shake and give wave readings geologists could use for drilling purposes. However, this was very destructive to the land. Today, special trucks are used to generate the vibrations needed to detect oil deposits. Similarly, offshore drilling uses a large air gun to create the measured vibrations.

Types of Imaging

With more sophisticated technology came the ability to make better images, and today geologists can make two-dimensional (2D), three-dimensional (3D) and four-dimensional (4D) renderings of drilling locations. The 2D seismic data is used to map out a location and develop a cross-section of the underground landscape. A 3D image is a much more realistic rendering of the seismic data, but it is also more costly, and 4D images build on the 3D picture, and add the ability to track changes to an area over time. These images would not be possible without computer-assisted exploration, or CAEX, which is used to organize the data into meaningful patterns.

Controversy

Even with the more environmentally friendly drilling exploratory practices, seismic exploration is not without its controversy. Much of debate centers on the use of air guns in offshore exploration. The guns are said to disrupt the migratory patterns of numerous species, particularly whales. Some studies have shown damage to the nervous systems of fish as well.