Page 93 - The Petroleum System From Source to Trap

84 Demaison and Huizinga

V e rtically Drained, Laterally Drained,
I
I
..
� High Impedance -� ... � -iooll � - - - - Low Impedance -------1�

L....-----'1 Shale seal
f.s_-=s=- �1 Shale (source rock)

Figure 4.9. Example of a supercharged, vertically drained, high-impedance petroleum system, patterned after the
Campeche-Reforma area, Mexico). The petroliferous part of the basin fill is vertically drained and has high impedance (left
side). ln contrast, the right side of the basin fill is laterally drained and shows low impedance but is petroleum poor.

O c e a n i c
T o p Oil Window

Figure 4.10. Example of a normally charged, vertically drained, high-impedance petroleum system, patterned after the Niger
delta, Nigeria. Sedimentary rocks in Tertiary deltas are usually vertically drained, due primarily to the presence of listric
faults.

Petroliferous basin fill in wrench-fault basins is also Magdalena Valley of Colombia, and the Carpathians).
characterized by multiple reservoir rocks charged by Prolific thrust belt plays are typically constrained by
deeply buried source rocks, with vertical redistribution effective top seals, such as the Fars salt in the Zagros fold
of the same type of petroleum through faults, as occurs belt, the highly overpressured shales in the eastern
in the Los Angeles and Ventura basins of California Venezuela thrust belt, and several thin evaporites in the
(Figure 4.11). overthrt belt of Wyoming.
Thrust belt provinces are also typical habitats for In summary, vertically drained petroleum systems
petroleum transfer by mostly vertical migration through share several common features:
breached seals, until a seal capable of containing the
accumulation is encountered (Figure 4.12). Most of the 1. Nearly all of the petroleum accumulations occur
world's prolific thrust belt plays are charged by a source over the pod of mature source rock or in close
rock that is significantly older and/or deeper than the proximity to it. Lateral migration distances are
reservoir rocks (e.g., Zagros fold belt, eastern Venezuela short (generally less than 30 km) (Sluijk and
thrust belt, overthrust belt of Wyoming, middle Nederlof, 1984).