5 - Thermal Maturity
Published online by Cambridge University Press: 10 May 2010
Summary
Do not the vast masses of basalt, the general appearances of mountain-ranges, the violent distortions and fractures of strata, the great prevalence of metamorphic action (which must have taken place at depths of not many miles, if so much), all agree in demonstrating that the rate of increase of temperature downwards must have been more rapid … in geological antiquity than in present age?
On the Secular Cooling of the Earth – Prof. William Thomson, 1862.The usual objective of thermal modelling is to identify the time and depth of hydrocarbon generation. Hydrocarbons are by-products of the metamorphism of organic material (kerogen) within sediments – a gradual process involving the expulsion of volatiles, gases, liquids and oils during the chemical alteration of buried organic matter. The thermal maturity of a rock is a measure of the degree to which this metamorphism has progressed.
Before we can make predictions about the timing of petroleum generation, we need to know two things. We need to understand the precise response of organic detritus to changes in thermal conditions, and we also need to know the thermal history of potential petroleum source beds. This chapter addresses those two requirements.
The Generation of Hydrocarbons from Organic Matter
The chemistry of converting organic matter into hydrocarbons is a whole separate field of expertise and is far too complex to investigate in great detail here. But a few words are necessary to illustrate the importance of temperature on the organic metamorphic process.
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- Crustal Heat FlowA Guide to Measurement and Modelling, pp. 146 - 204Publisher: Cambridge University PressPrint publication year: 2001