Science & Technology in Action

8th Edition

Finding Oil & Gas: Hydrocarbons & Seismic Prospecting


Jnr Science Cert
This lesson looks at some aspects of hydrocarbon exploration. It describes how hydrocarbons take the form of oil and gas, the conditions under which they become trapped in subsurface formations, and the use of reflection seismology and other technological developments in their discovery.
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Lesson excerpt

A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. The majority of hydrocarbons found naturally occur in crude oil (petroleum), where decomposed organic matter provides an abundance of carbon and hydrogen which, when bonded, can catenate to form seemingly limitless chains. Hydrocarbons can be gases (e.g. methane and propane), liquids (e.g. hexane and benzene), waxes or low melting solids (e.g. paraffin wax and naphthalene) or polymers (e.g. polyethylene, polypropylene and polystyrene). They can be saturated (alkanes) having no double or triple bonds or unsaturated with double (alkenes) or triple (alkynes) bonds between some of the carbon atoms. Most petroleum fuels are saturated hydrocarbons.

Countless micro-organisms live in the upper layers of the ocean, including algae, such as diatoms, and zooplankton such as copepods and other small crustaceans. When these organisms die their remains accumulate on the ocean floor along with those of other marine organisms. In this anoxic environment the organic matter decomposes and new polymers are formed and eventually become kerogen. Under the right conditions planktonic kerogen leads to the formation of petroleum, which may or may not be recoverable.

Sedimentary Basins
A sedimentary basin is any geological feature exhibiting subsidence and consequent infilling by a process known as sedimentation. Sedimentation causes mineral and/or organic particles to settle and accumulate, or minerals to precipitate from solution. With time (millions of years) and pressure (increased burial depths), organic matter within these sediments lead to the formation of hydrocarbons in the form of oil and gas.

True or False?

  1. A hydrocarbon compound consists entirely of hydrogen and carbon atoms. true
  2. Hydrocarbons form very long chains of molecules. true
  3. Petroleum is composed of unsaturated molecules. false
  4. Hydrocarbons are formed from aquatic forms of life. true
  5. Permeability is a measure of how much liquid a solid can hold. false
  6. A seal must not be porous. false
  7. A seal can be formed by chalk. true
  8. An anticline is a depression that can hold a residue of oil. false
  9. Geologists use explosions to generate seismic waves. true
  10. A seismic wave is completely reflected when it meets a change of rock type. false
  11. The reflected seismic wave is picked up by a geocomputer false
  12. “Bright Spot Analysis” shows bright spots where gas may be present. true
  13. A “wildcat well” is one drilled by an independent prospector. false
  14. After positive seismic testing there is at least a 50% chance of successful drilling. false

Glossary of terms

are photosynthetic organisms that occur in most habitats.
a saturated hydrocarbon
an unsaturated hydrocarbon which has at least one carbon—carbon triple bond between two carbon atoms.
a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen".
is a fold that is convex up and has its oldest beds at its core.