Crude oil and natural gas can rarely come to the surface of their own accord, with only a few historical examples including St. Quirinus’s oil at Tegernsee in Bavaria or the Burning Springs in North America. Most deposits of the two resources are located at depths of between 500 and 5000 meters and therefore hidden from sight below the surface of the earth. This makes discovering oil and gas a difficult challenge that can only be mastered by using state-of-the-art technology and at great cost. The development and exploration of new oil and gas fields require the cooperation of scientists from various disciplines, such as geologists, geophysicists, petrophysicists and engineers. 

First indications of possible deposits are found by analyzing aerial photographs taken from airplanes or satellites. Anticlinal domes are especially easy to make out from a bird’s eye perspective (this is where oil and gas are trapped under the dome of an impermeable layer of rock) and recently satellites have even been able to detect the presence of hydrocarbons, underground, i.e., oil or gas.  The satellites analyze the light reflected by the surface at different wavelengths (remote sensing direct detection of hydrocarbons, RSDD-H).

Magnetic fields help us look below the surface of the earth whereby these fields are weaker around a reservoir, as the sedimentary rock where oil and gas is trapped is less magnetic than rock of volcanic origin. These magnetic anomalies are also searched for using airplanes that are fitted with magnetometers, which are essentially long cables in which the fluctuations in the magnetic field create electric tension. Another method used is an indicator which measures the variation in the earth’s gravitational pull, a gravimeter.  These extremely sensitive scales on board an airplane measure any changes in gravity and provide important clues to geologists about the composition of the earth’s crust.

Seismology is the most important exploration technique revealing the different layers of rock that are below the surface. Scientists generate vibrations and use “earth microphones” (geophones) to measure the reflections of the sound waves at the interfaces between the layers of underground rock. The speed at which the waves propagate varies according to the type of rock and as a result, they hit the evenly distributed geophones at different times. Based on the pattern of delays, computers can generate two or three dimensional images of the layers of underground rock.

How are the vibrations generated? In the past, small explosive charges were used but today this task is performed by special trucks.  Underneath the truck there is a hydraulic vibration system which shakes the ground between five and eighty times a second. In 2010, Wintershall used the “vibrotrucks” to investigate the two Taoudeni exploration blocks in the Mauritanian desert. At distances of every 25 meters, the scientists inserted twelve geophones at each of a total of 61,400 points to capture the reflected sound waves. This was achieved by 180 people within a specialist expedition having for months to camp out in the Sahara.

If the seismic surveys produce promising results, the last exploration step that follows is a test well.  The test is the only way to establish with certainty that the investigated area has oil or gas deposits. Scientists drive drill bits deep into the ground and analyze the rock brought up to the surface. Drill cores are cut into wafer-thin slices and examined under the microscope. These thin sections provide important information, such as the composition of the rock and its storage properties. Yet, in spite of all the preparations with the latest measurement techniques as this stage oil and gas explorers can often be disappointed as  only every third to fourth test well will produce the desired result.