Where to find oil
Oil is usually accumulated in an oil traps called reservoirs. The oil is normally accompanied by natural gas and both are confined in a porous and permeable rock, which is usually composed of sedimentary rock. The gas, being lightest, occupies the top of the reservoir.
To find oil is not a trivial task and requires the collective work of different specialists: geologists, geophysicists, chemists, engineers. To find the specific geologic elements necessary to form an oil or gas trap under the subsurface requires a blend of science and art. In the past it was done by geologists who interpreted surface features and predicted locations of potential oil traps. Today geologists work closely with geophysicists and use different physical fields such as gravity, magnetics, electrical, seismic measurements to obtain information about the subsurface properties.
The most efficient and useful way for finding oil is the seismic exploration method. It consists in generating and injecting into the subsurface seismic/sound energy by seismic sources such as vibrators (land) or air guns (marine). Seismic waves reflect from subsurface rock formations and travel back to receivers called geophones (land) or hydrophones (marine). The wavefield information (travel times and amplitudes) of the returned seismic energy, integrated with existing borehole well information, aid geoscientists in estimating the structure, rock type and fluid content of subsurface formations, and allows them to determine the location of prospective drilling targets.