Page 11 - The Petroleum System From Source to Trap

�la g oon, L B, and W. G. Dow, eds., 199-!, The petroleum
svstem-from source to trap: AAPG Memoir 60.

Chapter 1

i The Petroleum System

Leslie B. Magoon Wall ace G. Dow
Bm11Ch of Pctrolcu111 Gcologrt OGSI
U.S. Geological Sun•Clf The Woodla11d,, Tc.ra,, U.S.A.
Mc11lo Park, California, U.S.A.

Abstract
Sedimentary basins, petroleum systems, plays, and prospects can be viewed as separate levels of
investigation, all of which are needed to better understand the genesis and habitat of hydrocarbons.
Sedimentary basin investigations emphasize the stratigraphic sequence and structural style of sedi­
mentary rocks. Petroleum system studies describe the genetic relationship between a pod of active
source rock and the resulting oil and gas accumulations. Investigations of plays describe the
present-day geologic similarity of a series of present-day traps, and studies of prospects descrbe the
individual present-day trap. Except for the petroleum system, these terms are widely used by
petroleum geologists. l11e procedure to identify, characterize, name, and determine its level of
certainty is discsed.
A petroleum system encompasses a pod of active source rock and all related oil and gas and
includes all the essential elements and processes needed for oil and gas accumulations to exist. The
essential elements are the source rock, reservoir rock, seal rock, and overburden rock, and the
processes include trap formation and the generation-migration-accumulation of petroleum. All
essential elements must be placed in time and space such that the processes required to form a
petroleum accumulation can occur.
The petroleum system has a stratigraphic, geographic, and temporal extent. Its name combines
the names of the source rock and the major reservoir rock and also expresses a level of certainty­
known, hypothetical, or specutive. Four figures and a table that best depict the geographic, strati­
graphic, and temporal evolution of a petroleum system include a burial history chart to establish
the age and critical moment of the system, a map and a cross section drawn at the critical moment,
an events chart to summarize the formation of the petroleum system, and a table of related accumu­
lations. The petroleum system can be used as an effective model to investigate discovered hydro­
carbon accumulations.

INTRODUCTION on! y in the past 10-15 years. Second, the petroleum
system approach is a way of organizing information that
uniquely lends itself to efficient investigations for
New ideas are constantly being developed and put to purposes of exploration, resource appraisal, and
use in oil and gas exploration. Even more common than research. Third, the role of petroleum system investiga­
the development of new ideas is the revival of older tions in basin analysis, play analysis, and prospect
concepts, which are then put to use in new ways. The appraisal has never been adequately clarified.
concept of the petroleum system is one that many geolo­ In addition to providing an introduction to this
gists are intuitively familiar with and may feel that they volume, the purposes of this paper are as follows: (1) to
have been using all along. There are several reasons why define, compare, and contrast the different levels of
we are now proposing to revive, expand, define, and petroleum investigations; (2) to describe the history of the
formalize this concept. First, the ability to identify a petroleum system model; (3) to identify, name, and
petroleum system uniquely depends on geochemical determine the level of certainty of a petroleum system; (4)
techniques needed to map organic facies, to understand to describe those figures that best depict the geographic,
and map hydrocarbon shows, and to carry out stratigraphic, and temporal extent of a petroleum system;
petroleum-petroleum and petroleum-source rock corre­ and (5) to describe how a petroleum system study is
lations, some of which were put into widespread use implemented.

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