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.