Geologists look for 4 main points in the rock formations.

Source rocks: Sedimentary rocks containing organic material that over time forms the hydrocarbons.

Trapping structures / cap rocks: Hydrocarbons will migrate upwards molecule by molecule as they are formed. They travel upwards through permeable rock until they come against a are trapped against a non permeable rock, often shaped in such a way as to act like an upside down container.

Reservoir Rocks: This is the section of permeable rock below the trapping structure where the hydrocarbons have collected after ending their journey upwards from the source rock.

Geological techniques include looking at the actual surface of the area under consideration if on land. his can be done by actually visiting the area, using aerial photographs or satellite images. The main source of information is the seismic survey.

On water, a survey ship tows hydrophones on long lines out the back of the ship. Loud sounds are produced from the ship, directed towards the sea bed. These sound waves, penetrate the Earth, bounce back off the sea bed and various rock layers. The data received can be interpreted by computers to give a picture of rock formations.

All this information is accumulated and petroleum geologists can estimate the likelihood of hydrocarbons being present in viable quantities at the location being examined. They can not see oil or gas, rather they can see rock formation patterns that can suggest the possibility of oil and gas being present. Even today, they do not always get it right. With all the information and technology at the disposal of oil companies, there is no way to be 100% sure that there is oil or gas in a location, other than to drill.

As computer power has improved and seismic tools are able to send more complex sound patterns in to the Earth's crust, the images have improved the accuracy.

Once everyone concerned has decided to invest in a location, a drilling rig is hired to find out if they were right.

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Pablo Manente
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Pablo writes about Africa, oil, politics, human rights and many other subjects. He is a full time... »

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