Page 17 - The Petroleum System From Source to Trap

1. The Petroleum System 9

accumulated hydrocarbons whose provenance was the hydrocarbon generation, migration, and accumulation
mature source rock is shown to apply for generative are distinguished from essential elements and are
basins worldwide. Second, risk can be reduced by expressed as a single process. Last, the essential elements
staying close to the mature source rock where the drilling are shown in their figure 2 to be the source rock,
success ratio is highest. Three, unlike the oil system, the reservoir rock, seal rock, and trap.
generative basin can have one or more petroleum gener­
ating depressions as well as one or more source rocks. Ulmishek's Independent Petroliferous
System
Meissner's Hydrocarbon Machine
In Ulrnishek (1986), the term independent petroliferous
In Meissner et al. (1984, p. 1), the term hydrocarbon system (IPS) was used to describe the "stratigraphic
machine is defined as follows: aspects of petroleum resource assessment." In the
abstract (p. 59), they state that IPS is
Sequences which contain all of the elements involved in the
process of hydrocarbon generation from source rock to conse­ . . . understood here as a body of rocks separated from
quent migration and accumulation constitute what may be surrounding rocks by regional barriers to lateral and vertical
termed natural geologic hydrocarbon machines. migration of fluids, including oil and gas. Stratigraphically, an
IPS is essentially homogeneous. It includes source rocks,
They go on to say (1984, p. 1) that
reservoir rocks, traps, and a regional seal, and thus, it is a
suitable unit for comparative analysis of the factors and
Use of this conceptual framework will allow the prediction of
petroleum genetic studies. For oil and gas resource assessment
generation/ migration/accumulation cells or hydrocarbon in poorly known regions, an IPS has certain advantages over a
machines operative in certain portions of the stratigraphic basin or play as an assessment unit. The concept of an IPS can
secton. This predictive ability, when used in conjunction with also be used in statistical methods of resource appraisal and can
regional source rock distribution maps, will explain the distribu­ increase reliability of these results.
tion of hydrocarbon accumulations already found and lead to
the further delineation of prospective areas.
In expanding his definition, Ulrnishek (1986, p. 61-62)
Meissner et al. (1984, p. 1-2) expand on their definition goes on to say that
of hydrocarbon machine in the explanation of a figure:
It is evident that three of the four major factors controlling a
region's petroleum riclmess (source, reservoir, and seal) contain
The starting point of the diagram concerns the existence of a
source rock from which the hydrocarbons originate, the factors much more stratigraphic than tectonic information. The fourth,
controlling its deposition and composition, and the types of the trap factor, tends to reflect both stratigraphy and tectonics
depending on the type of trap. It seems reasonable, therefore,
hydrocarbons it may generate under conditions of thermal that a unit chosen for comparative assessment of petroleum
maturity. The following parts of the diagram concern the resources should be more related to the stratigraphy of an area
controls that time, stratigraphy, structure, and fluid dynamics than to the tectonics. The analysis of factors of richness in such a
exert on the processes of hydrocarbon migration and accumula­ unit will be an easier task than the analysis of these factors in
tion. any tectonic unit that is "heterogeneous" from a stratigraphic
All of the factors which affect the processes of hydrocarbon point of view. Because the four listed factors reflect the condi­
generation, migration, and accumulation constitute elements of tions for successive processes of generation, accumulation, and
a total system which may be described as a machine. These preservation of oil and gas, such a unit must meet two major
elements are placed in their interdependent cause-and-effect requirements: (1) it must be a confined system in which these
context in the schematic diagram of Figure 2. The illustration of processes take place independently from surrounding rocks,
a plumbing system involving a typical hydrocarbon machine and (2) it must be the simplest of these systems, to provide
depicts the movement of fluids outward from their site of gener­ maximum internal geologic uniformity and to permit sufficient
ation within an area of thermal maturity to carrier/reservoir depth of analysis. Such an assessment unit is here called an
beds in which they migrate and to sites of accumulation in traps. independent petroliferous system (IPS), which is defined as a
continuous body of rocks separated from surrounding rocks by
Figure 2 of Meissner et al. (1984, p. 3) shows a regional barriers to lateral and vertical migration of liquids and
diagram of the hydrocarbon machine, which is captioned gases (including hydrocarbons) and within which the processes
as follows: of generation, accumulation, and preservation of oil and gas are
essentially independent from those occurring in surrounding
Diagrammatic model of a hydrocarbon machine showing rocks.
geometric arrangement of essential elements and fluid
migration patterns characterizing the internal "plumbing" At the end of this same section, he (1986, p. 62) states the
system. The function of such a machine is to turn organic matter following:
in a source rock (raw material) into a hydrocarbon accumulation
(finihed product). The most important task in developing the proposed approach
is the determination, for analog purposes, of IPSs in well­
Meissner et al. (1984) make the following points. First, explored basins. At present, 40-50 well-explored basins
the "generation/migration/accumulation cells or hydro­ worldwide certainly contain not less than 150-200 IPSs. These
carbon machines" are very similar to the oil systems of could provide an excellent file of analogs with most combina­
Dow (1974) (although they fail to reference his work) and tions of factor types. Volumetric yields of the well-studied IPSs
to the petroleum system of Perrodon (1980, 1983a,b) and could serve as a basis for the evaluation of undiscovered
Perrodon and Masse (1984). Second, the processes of resources of the forecast IPSs.