This chapter defines petroleum systems and provides examples of the geology, stratigraphy, and geochemistry of source rocks and crude oils through geologic time. Gas chromatograms, sterane and terpane mass chromatograms, stable isotope compositions, and other geochemical data are provided for representative crude oils generated from many worldwide source rocks.
PETROLEUM SYSTEM NOMENCLATURE
Traditional exploration focuses on subsurface traps and the play concept in sedimentary basins that are described according to tectonic style. A play consists of prospects and fields with similar geology (e.g. reservoir, cap rock, trap type). Plays use the characteristics of discovered accumulations to predict similar undiscovered accumulations. Focus by interpreters on a particular play type, as in anticline or pinnacle reef trends, may limit creative ideas on other potential play types. Furthermore, although generalizations can be made about many variables affecting basins of a given tectonic style, such as field size, heat flow, and the effectiveness of traps for retaining petroleum, source-rock richness and volumes are related only weakly to tectonic style. Therefore, tectonic classifications are of little value in order to forecast petroleum volumes (Demaison and Huizinga, 1994). The key elements needed to forecast petroleum volumes, such as source, reservoir, and seal rock, and adequate generation, migration, and accumulation factors, were incorporated into the petroleum system concept, as discussed below.
The petroleum system concept was first expressed in terms of oil—source rock correlation (Dow, 1974), as petroleum systems (Perrodon, 1980), generative basins (Demaison, 1984), hydrocarbon machines (Meissner et al., 1984), and independent petroliferous systems (Ulmishek, 1986).