Page 18 - The Petroleum System From Source to Trap

10 Magoon and Dow

In a discussion of an IPS as an assessment unit, adds new words where necessary to clarify a petroleum
Ulmishek (1986, p. 62) states that system. The levels of petroleum investigation (Magoon,
1 9 89b) are introduced to distinguish the petroleum
An IPS is purely an assessment unit; its application for other system from the sedimentary basin, play, and prospect.
purposes is limited. As an assessment unit, however, it has
significant advantages over two other such units that are widely
used in practice: the play, or petroleum wne, and the basin. Magoon and Dow's Petroleum System
He later observes (1986, figure 3D, p. 66) that when an The petroleum system is predicated on the synthesis
1
analysis of drilling statistics is carried out by IPS, rather of previous work (Table . 2). The terms sedimentary basin,
than by drilling depth in a basin, it becomes clear that play, and prospect have been informally used by
poorly explored IPSs have potential for undiscovered petroleum geologists prior to the advent of modem-day
commerical oil and gas accumulations. organic geochemistry to explain the habitat of hydrocar­
Ulmishek' s ( 1 986) paper either states or implies bons. Early work in organic geochemistry by Trask and
several points. (1) The IPS is similar to the oil system of Wu (1930), Triebs (1936), Hunt and Jamieson (1956), and
Dow (1974) and the hydrocarbon machine of Meissner et Phillipi (1957) provided ways to measure and map
al. (1984) (although neither is referenced). (2) The major source rocks and associated products. To understand a
f a ctors (source rock, trap, reservoir rock, and seal) are the petroleum system, a working knowledge of petroleum
same as the essential elements of Meissner et al. (1984). geochemistry is essential.
(3) All major factors are stratigraphic in nature except for Dow (1974) distinguished a play from the oil system
trap, which is mainly structural. (4) Major factors are based on geochemistry. Ulrnhek (1986) recognized the
distinguished from processes (generation, accumulation, (independent) petroliferous system as a separate unit
and preservation) when referring to the assessment unit distinct from the sedimentary basin and play. Magoon
(IPS). The process of migration is absent, and preserva­ (1989b) identified the levels of petroleum investigation as
tion is an addition when compared to Meissner et al. basin studies, petroleum systems, plays, and prospects.
(1984). (5) The IPS is only considered an assessment unit. The present volume refers to the sedimentary basin,
(6) The paper points to "two other such units that are petroleum system, prospect, and play.
widely used in practice: the play, or petroleum zone, and The term petroleum system was chosen because
the basin." (7) Breaking out the drilling statistics so that petroleum includes all forms of hydrocarbons (solid,
new IPSs are more clearly identified is a sage observa­ liquid, or gaseous) (Levorsen, 1967) and system accounts
tion. for the interdependence of the essential elements (source
rock, reservoir rock, seal rock, and overburden rock) and
Magoon's Petroleum System processes (trap formation and generation-migration­
accumulation of petroleum). The term has been used
Magoon (1987) first used the term elements to refer to before by Perrodon (1980, 1983a,b) and Perrodon and
source rock, migration path, reservoir rock, seal, and trap Masse (1984) in a way that is consistent with our use. The
and explains that the elements "must be placed in time term essential elements originates from Meissner et al.
and space such that a petroleum deposit can occur." To (1984) and Ulrnishek (1986), and processes are formalized
identify a petroleum system, Magoon (1987) relied on in Meissner et al. (1984) and Ulrnshek (1986).
oil-source rock correlation. The name of the petroleum The uniqueness of a petroleum system is based on
system included the name of the source rock and major petroleum-source rock correlation and is named
reservoir rock followed by the level of certainty. He clas­ according to Dow (1974), whereas the level o f certainty is
sified the systems using certain criteria. according to Magoon (1987, 1 9 88, 1 9 89a,b). The
In Magoon (1988, table 1, p. 3), an attempt was made geographic and stratigraphic distribution as well as the
to put the petroleum system into historical perspective preservation time of the petroleum system is specified by
using a table that summarized the contribution of Dow Magoon (1988). The definition of the petroleum system
(1974), Bois ( 1 975), White (1980), Bois et al. ( 1 982), used in this volume is a refinement of previous work.
Demaison (1984), Meissner et al. (1984), Ulrnshek (1986),
and Magoon (1987). The table specified the geologic
parameters and evaluation criteria discussed by each PETROLEUM SYSTEM DEFINITIONS
author. Magoon (1988, p. 2) states that AND CHARACTERISTICS
The petroleum system emphasizes the genetic relation between A petroleum system is defined here as a natural system
a particular source rock and the resulting petroleum accumula­ that encompasses a pod of active source rock and all
tion; basin studies emphasize structural depressions and the related oil and gas and which includes all the geologic
included sedimentacy rocks regardless of the relation to any
petroleum deposits; and the play or prospect approach empha­ elements and processes that are essential if a hydro­
sizes whether the present-day trap is detectable with available carbon accumulation is to exist. This once-active source
technology or tools. rock may now be inactive or spent (depleted). Petroleum
here includes high concentrations of (1) thermal or
The most recent definition of a petroleum system and biogenic gas found in conventional reservoirs or in gas
classification scheme can be found in Magoon (1989a). hydrate, tight reservoirs, fractured shale, and coal; or (2)
The definition incorporates previous contributions and condensates, crude oils, and asphalts found in nature.