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The AAPG/Datapages Combined Publications Database

CSPG Special Publications


Facts and Principles of World Petroleum Occurrence — Memoir 6, 1980
Pages 143-152
Geological and Geochemical Principles of Petroleum Occurrence

Principal Factors Controlling the Timing of Petroleum Generation

B. P. Tissot, J. F. Bard, J. Espitalie


Timing of petroleum generation is mainly controlled by burial depth and geothermal gradient. Time and temperature, to a certain degree, can be mutually compensatory in oil and gas formation. The rate of subsidence and the geothermal gradient determine the temperature-time relationship.

Use of a mathematical model of petroleum generation allows us to calculate the amount of oil and gas generated as a function of time. This is done for several geological situations such as constant rate of subsidence or several cycles of sedimentation. The different types of organic matter may also affect, to some extent, the temperature and time threshold of oil generation. A comprehensive study of examples from Europe, Africa, North America and Asia shows that the principal phase of oil generation may follow source rock deposition after a delay of a few millions to 300 Ma. These conclusions are based on geological considerations and geochemical analyses of the organic matter and confirmed by use of the mathematical model. In some instances, the geological setting allows one to check the results of the model.

Finally, it is concluded that most of the present oil fields have been formed during the Cretaceous and Tertiary regardless of the source-rock age.

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