Journal of Petroleum Geology, Vol.6,
No.1, pp.39-54, 1983
©Copyright 2000 Scientific Press,
Ltd.
ABUNDANCE OF SOURCE ROCKS
FOR OIL AND GAS WORLDWIDE
Hans R. Grunau*
*Petroconsultants S. A., 8-IO, rue
Muzy, Case postale 228, 1211 Geneva 6, Switzerland.
Abstract
Source rock abundance through geological
time cannot be measured in absolute quantitative terms. The
source rocks of giant fields, which are known inmost cases, can
serve as an appropriate yardstick for a percentage allocation of
source rocks to geological time intervals, based on ultimately
recoverable reserves. This yardsick is used to relate source rock
percentages per time interval to in situ reserves and resources
of oil and gas worldwide, both conventional and unconventional.
Necessary corrections are made. On this basis it appears that the
Cretaceous is the most important oil-generating period (49%),
while the Tertiary is the most important gas-generating period
(76%). For total hydrocarbons in terms of oil equivalents, the
most important hydrocarbon-generating intervals are the Tertiary
(69%), followed by the Cretaceous (25%), the Jurassic (4%) and
the Triassic to Paleozoic (2%). The percentages refer to
source-rock age and not to time of generation. All estimates have
to be regarded with much caution. They represent an approach to
the problem rather than a solution. Major uncertainties still
exist. It must be stressed that the problem of source rock
abundance should be seen in a wider hydrocarbon habitat context,
especially in the light of retention. The important role of
bacterial gas and gas hydrates is emphasized.
