[Quiz] How We Find Crude Oil Reservoirs

The search for crude oil begins with geologists who study the structure and history of rock layers below the earth's surface to locate areas that may contain deposits of oil and natural gas. 

Major surveys to locate oil

Magnetometric surveys: Magnetometers hung from airplanes measure variations in the earth’s magnetic field in order to locate sedimentary rock formations which generally have low magnetic properties when compared to other rocks.

Aerial photogrammetric surveys: Photographs taken with special cameras in airplanes, provide three-dimensional views of the earth which are used to determine land formations with potential oil and gas deposits.

Gravimetric surveys: Large masses of dense rock increase the pull of gravity, gravimeters are used to provide information regarding underlying formations by measuring minute differences in gravity.

Seismic surveys: Seismic studies provide information on the general characteristics of the subsurface structure. Measurements are obtained from shock waves generated by setting off explosive charges in small-diameter holes, from the use of vibrating or percussion devices on both land and in water, and from underwater blasts of compressed air. The elapsed time between the beginning of the shock wave and the return of the echo is used to determine the depth of the reflecting substrata. The recent use of super-computers to generate three-dimensional images greatly improves the evaluation of seismic test results.

Radiographic surveys: Radiography is the use of radio waves to provide information similar to that obtained from seismic surveys.

Stratigraphic surveys:  Stratigraphic sampling is the analysis of cores of subsurface rock strata for traces of gas and oil. A cylindrical length of rock, called a core, is cut by a hollow bit and pushed up into a tube (core barrel) attached to the bit. The core barrel is brought to the surface and the core is removed for analysis.

If a site seems promising, an exploratory well is drilled and tested. If enough oil is found to make it financially worthwhile to pursue, development wells are drilled. The type of well that is drilled depends on the location, geology, and oil resource.