Reflection Seismic Method

Introduction 

The reflection seismic method is among the most common geophysical methodology used for obtaining subsurface geological information. The method uses the principle of seismology to estimate the properties of the Earth’s subsurface from reflected seismic waves. In terms of signal processing capabilities and data acquisition, the method exhibits the highest degree of technical sophistication. The method provides a 2-dimensional or 3-dimensional imagery of geological structure and stratigraphic boundaries at depths that range from hundreds of meters to several kilometers in depth. 

Why the Reflection Seismic Method is the Tool of Choice for Oil and Gas Exploration 

Reflection seismic method is one of the most preferred techniques for obtaining subsurface geological information. The method has been in existence since 1930 and is widely used today and has had proven capabilities for almost two decades. The reflection seismic method is the tool of choice for oil and gas exploration compared to other geophysical tools. This is because the method has a good signal penetration, which makes the geophysical tool capable of imaging deep targets and structures. This benefit has made the mining industry to take advantage of the reflection seismic method and seek solutions to their prospective problems. Another feature that makes the reflection seismic method the choice for oil and gas exploration is that it can be used to image crystal structures. Understanding the geometry of crystal structure is essential as it can be applied to assess risks of natural hazards and be used to study geodynamical processes. It can also be used to detect mineral deposits associated with geological structures. 

Application of Reflection Seismic Waves

The reflection seismic is widely applied in the oil and gas industry to search for the commercially economic deposit of crude oil, natural gas, and minerals. The oil and gas industry uses this method to record, process, as well as interpret the artificially induced waves in the earth. Vibratory mechanisms mounted on specialized trucks are used to generate artificial seismic energy. “Seismic waves reflect and refract off subsurface rock formations and travel back to acoustic receivers called geophones” (BNK Petroleum, N.d). The reflection seismic method consists of determining the travel time of seismic energy from surficial shots through the surface to an array of ground motion sensors. 

“Each stratigraphic layer within the Earth reflects a portion of the energy and allows the rest to pass through” (BNK Petroleum, N.d). Figure 1 shows an illustration of how acoustic waves travel and recorded. The reflected energy waves recorded by the geophones at the surface can be used to analyse the structure of the rocks hidden beneath the surface. After the geophones record the reflected energy waves, they are subjected to further processing before being interpreted. 

Fig. 1: Illustration of how the oil and gas industry uses the reflection seismic method to analyze the structure of the rocks hidden beneath the surface. Retrieved from: BNK Petroleum. 

Once the processing is complete, a 2-dimensional profile, such as the one shown in Figure 2, is produced. 

Figure 2: Seismic Profile. Retrieved from: BNK Petroleum. 

Geoscientists use the seismic profile produced together with other available information to generate maps of the rocks and subsurface structures available beneath the earth. Geoscientists can then use these maps to accurately position the exploration wells to determine the location of the oil and gas deposits. Figure 3 is an illustration of the maps produced from the seismic profile. 

Figure 3: Maps. Retrieved from: BNK Petroleum. 

References

BNK Petroleum. (N.d). Seismic Exploration. [Online]. Available at: https://www.bnkpetroleum.com/operations/technical-description/seismic-exploration . Accessed 24 th April 2019.