Journal of Petroleum Geology, Vol.7,
No.3, pp.303-312, 1984
©Copyright 2000 Scientific Press,
Ltd.
PETROLEUM FORMATION AND
THE THERMAL HISTORY OF THE EARTH'S
SURFACE +
C. E. Melton* and A. A. Giardini**
* Department of Chemistry,
University of Georgia, Athens, Ga. 30602, USA.
**Department of Ceology,
University of Georgia, Athens, Ga. 30602, USA.
Abstract
Petroleum reservoirs are known to depths of
~ 10 km, and their ages extend to ~ 700 m.y. Since temperature is
important to petroleum-forming processes, the thermal history of
this region is analyzed. From the geologic record, average
surface temperature values are derived for recent geologic time
and 2.5 b.y .BP. These data are applied to the Newton cooling law
to obtain a value of 2.63 x 10(-11)yr(-1) for the heat transfer constant of the Earth
surface/space system. This, in turn, yields an approximate
average cooling rate for the surface of 7¡C per b.y. Profiles of
average surface temperature over geologic time are constructed
for high, middle and low latitudes. Respective initial average
surface temperatures at these latitudes were 13.6¡, 41.6¡ and
59.6¡C. Two tests are applied to the cooling curves to check
their validity. First, they are used with the rate constant for
the mantle outgassing of water vapour and the Clausius-Clapeyron
equation to calculate the accumulation and average temperature of
liquid surface water over geologic time. The results are
consistent with the geologic record pertaining to the history of
water-borne sediments, glaciation and life. Second, the
calculated thermal characteristics of the surface are compared
with published date for the mantle. They agree to within 2%. The
surface average cooling-rate, applied to the average geothermal
gradient of the crust, gives a value of <10¡ C. for the
temperature change of a petroleum reservoir buried at a depth of
10 km over the past 700 m.y. The change for reservoirs either
younger or less deep (or both) would be less. These results
indicate that the importance of reservoir age to petroleum
-forming processes lies mainly in the increased opportunity for
geologic change such as depth of burial or igneous activity that
would alter conditions within the reservoir.
