July 5, 2024

Seismic Survey; a Widely Used Method of Investigating Subterranean Structures

Seismic Survey is a method of investigating subterranean structure, particularly to locate minerals and petroleum. It involves sending seismic waves through the ground, causing them to reflect off of underground formations and return to the surface. By analyzing the reflected waves and their speed of travel, a geologist or geophysicist can construct a map of the Earth’s shallow structure. It can also determine what kind of rocks are in the area and whether they might contain valuable resources.

The technique is not new; it was first developed by seismologists in the late 19th century. Since then, it has become the dominant exploration method used by oil and gas companies to locate underground deposits. It is also used in the search for waste-disposal sites, to determine the stability of land for industrial facilities, and to explore archaeological sites.

In the case of oil and gas exploration, it is hoped that by knowing what kind of rock layers are in an area, a company can estimate how much crude or natural gas is trapped beneath the surface and where the best place to drill would be. The method has a number of advantages over other techniques, such as core drilling and sampling, however, is very expensive. Due to this, it is important to get the data as quickly and accurately as possible, so that a company can make an informed decision.

The worldwide Seismic Survey Market is expanding due to benefits of seismic surveys include a decreased risk of drilling dry wells, which would preclude future drilling, and a reduction in the environmental consequences of oil and gas development.

To obtain seismic data, energy sources are placed in a grid over the area to be surveyed and receiver points – to record the reflected waves – are positioned a short distance away. The energy sources can be small explosive charges set off in holes in the ground (shot holes), electric vibrators (known as thumpers), or vehicles equipped with metal plates that vibrate the body of the truck (Vibroseis trucks). The signals received at the receiver points are transmitted along cables to recording trucks that control the firing of the energy source and then record the resulting wave information on magnetic tapes.

The key to a good Seismic Survey is to use the right type of source. A vibration source produces pressure waves that will propagate much further than an impact type such as a hammer or weight drop. The optimum frequency signature is also important. A high frequency wave will provide greater detail, whereas a low frequency wave will provide excellent depth penetration but may be attenuated too quickly to give good resolution.

This information is interpreted by geologists or geophysicists using complex computer software to produce 3D images of the shallow structure of the earth’s subsurface. These images can be viewed on a computer screen and can reveal details that would otherwise be hidden from view. The process is time consuming and labor-intensive, and the results are not guaranteed to be successful. However, even a single misstep can be costly, as resurveying the area must often be done from scratch.

Reflection surveys are the most common form of exploration Seismic Survey. They provide good quality data and are suitable for a wide range of applications, including 2D seismic section mapping and establishment of basement faults (e.g. Zeegt lignite coal basin, India) and massive metallic mineral deposits (Munni Munni platinum-group element deposit, Australia, Kevitsa nickel-copper and gold deposit, Finland, Bathurst zinc-gold mining camp, Canada).

Currently, offshore oil and gas exploration uses deafening seismic testing that involves powerful airguns blasting the seas at 10-second intervals to map offshore oil and natural gas reserves. The blasts cause significant noise pollution, disrupting whales and dolphins’ ability to communicate, disturb critical behaviors such as mating and foraging, and mask their hearing. They also harm and kill marine wildlife every day around the clock for years at a time.