How is oil located?

Geologists are key to helping find oil. They are tasked with looking and finding the right conditions for an oil trap. An oil trap constitutes of 5 components.

1.      Source rock

2.      Cap rock

3.      Reservoir rock

4.      Migration

5.      Maturation

If these 5 components are not fulfilled, then there might not be oil. Migration and maturation are key processes within the formation of an oil reservoir.

Even so not all rocks will contain oil. Only a rock with a high organic carbon content, under the right thermal conditions will generate petroleum.

Geologists also use previous historical geological events/occurrences within the rock to determine if there is oil. They examine surface rocks and terrain with the help of satellite images as well as interpret surface features, surface rocks and soil types.  They also incorporate sensitive equipment such as gravity meters and sniffers. Gravity meters measure tiny changes in the earth’s gravitational field which could be an indication of flowing oil. Sniffers are like small electrical noses and are used to detect the smell of hydrocarbons. However, the most commonly used method is seismology. This involves creating shock waves that pass through rock layers and interpreting the waves that are reflected back to the surface.

The following equipments are utilised in seismic surveys to create the shock waves;

-   Thumper trucks – for overland exploration. This involves slamming heavy plates into the ground.

-       Compressed air guns - for overwater exploration. These are used to shoot pulses of air into the water.

-       Explosives – can be used for overland or over water exploration. However, the way in which they are employed is different. For overland exploration, the explosives are detonated after being drilled into the ground. For over water exploration, they are thrown overboard and explodes.

The shock waves emitted travel beneath the surface of the earth and are then reflected back by various rock layers. The reflections are dependent on the type and density of rock layers through which they are passing and hence travel at different speeds. The reflected shock waves are detected then by vibration detectors or sensitive microphones, the results of which are then refined and interpreted by geologists.

Once a prospective oil reservoir is established, geologists mark the location using GPS coordinates for overland exploration or marker buoys for over water exploration.

Stay tuned for the next blog post on the different geoscientists i.e geophysicists and geochemists!