What is a geophysicist?

How is a geophysicist trained?

Geophysicists are trained mathematicians, physicists and computer specialists. They all acquire a good grounding in descriptive geology to enable them to work closely with geologists in order to generate images of petroleum traps from the data collected.

What tools does a geophysicist use?

Geophysicists use a variety of methods, depending on the geological object they wish to visualize. During initial reconnaissance of unexplored terrain, they may detect geological structures that can stretch over several miles, such as a basin's non-visible limits. They use "potential" methods, plotting their measurements on topographical maps.

These include:

  • geomagnetism, which studies the variation of the direction and intensity of the Earth's magnetic field caused by magnetic differences between different rocks. These measurements are carried out on the ground and from the air (in aircraft flying back and forth across the zone to be explored).
  • gravimetry, which employs the same procedures as above, but which analyzes the often infinitesimal variations in the Earth's gravitational field.

Once the contours and depth of the sedimentary basin have been ascertained, seismic refraction, and more often seismic reflection techniques, are used. These methods measure very precisely the travel time of sound waves generated by a shock dropping a heavy weight, a mechanical vibrator, a bubble of high-pressure air; ... or via an explosion applied to the ground or in the sea. The shock wave is reflected by the geological strata back to the surface, where it is picked up by an acoustic sensor called a geophone (or hydrophone at sea). If the point from which the sound wave was generated, and the speed at which it travels through the different rocks are known, then one can deduce the depth of the stratum from which the wave was reflected. By plotting all of the points identified on a grid covering the topographical map, one can map the depths of the main strata.

A geophysicist's tasks

Geophysicists work in the field, which may be onshore or off, or else in the oil company's scientific and technical center. In the field, they record data relating to the depth of geological strata and other features. Powerful computers are needed to record and process the raw data, which contain a mass of extraneous noise inherent in this technique. Geophysical technicians supervise this task, which is painstaking and often expensive, especially when the terrain is covered in dense vegetation.

Geophysical engineers at the company's technical center use mathematical methods to process these numerical data in order to generate seismic sections and maps - to render these data comprehensible to humans. Present-day high-powered computer methods are so precise the resulting seismic section resembles the image produced in a hospital scanner. Like a physician, the geophysicist interprets the image to extrapolate the geometry of the petroleum trap. Interpretation is carried out in constant collaboration with geologists, who are able to identify the type of formation and describe its characteristics.

As in geology, certain geophysicists seek to improve on existing techniques in data acquisition, and mathematical processing, as well as seeking to develop new techniques and methods. In this latter capacity, they contribute to overall improvements in exploration performance.

Additional specialities

Like drilling engineers and geologists, geophysicists work with a variety of other specialists, e.g.:

  • geologists, (their usual partners);
  • reservoir engineers, since modern seismic methods are capable of imaging certain details inside a petroleum reservoir, size permitting;
  • geophysical service companies. In addition to data recording, these firms offer a growing range of data pre-processing services, including interference noise elimination and preliminary data organization.