Text 7 Seismic Exploration
The practice of natural gas and oil deposits has been transformed dramatically in the last 15 years with the advent of extremely advanced, ingenious technology. Unarguably the biggest breakthrough in petroleum and natural gas exploration came through the use of basic seismology. Seismology refers to the study of how energy, in the form of seismic waves, moves through the Earth's crust and interacts differently with various types of underground formations. In 1855, L. Palmiere developed the first 'seismograph', an instrument used to detect and record earthquakes. This device was able to pick up and record the vibrations of the earth that occur during an earthquake. However, it wasn't until 1921 that this technology was applied to the petroleum industry and used to help locate underground oil formations.
The basic concept of seismology is quite simple. As the Earth's crust is composed of different layers, each with its own properties, energy (in the form of seismic waves) traveling underground interacts differently with each of these layers. These seismic waves, emitted from a source, will travel through the earth, but also be reflected back towards the source by the different underground layers. It is this reflection that allows for the use of seismology in discovering the properties of underground geology. Geophysicists are able to artificially create vibrations on the surface and record how these vibrations are reflected back to the surface.
An analogy that makes intuitive sense is that of bouncing a rubber ball. A rubber ball that is dropped on concrete will bounce in a much different way than a rubber ball dropped on sand. In the same manner, seismic waves sent underground will reflect off of dense layers of rock much differently than extremely porous layers of rock, allowing the geologist to infer from seismic data exactly what layers exist underground and at what depth. While the actual use of seismology in practice is quite a bit more complicated and technical, this basic concept still holds.
Ex 1 Answer the questions:
When was seismic exploration used for the first time?
Who invented the seismograph?
For what purposes can it be used?
Can you explain the basic concept of seismology to a six year-old child?
Text 8 Onshore and Offshore Seismology
Ex.1 Read the text “Onshore and Offshore Seismology” and ask the questions you might ask about.
onshore, adj. –береговой
offshore, adj- морской, на некотором расстоянии от берега
log, v – производить каротаж
In practice, using seismology for exploring onshore areas involves artificially creating seismic waves, the reflection of which are then picked up by sensitive pieces of equipment called 'geophones', imbedded in the ground. The data picked up by these geophones are then transmitted to a seismic recording truck, which records the data for further interpretation by geophysicists and petroleum reservoir engineers. The drawing shows the basic components of a seismic crew. The source of seismic waves (in this case an underground explosion) creates vibrations which reflect off of the different layers of the earth, to be picked up by geophones on the surface and relayed to a seismic recording truck to be interpreted and logged. Although the seismograph was originally developed to measure earthquakes, it was discovered that much the same sort of vibrations and seismic waves could be produced artificially and used to map underground geologic formations. In the early days of seismic exploration, seismic waves were created using dynamite. These carefully planned, small explosions created the requisite seismic waves, which were then picked up by the geophones, generating data to be interpreted by geophysicists, geologists, and petroleum engineers.
