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Impact of the Hercynian Orogeny on Hydrocarbon
Accumulations in
Faqira, Mohammad, Martin Rademakers,
Abulkader Afifi, Saudi Aramco,
Recent well and
seismic data confirm that most Saudi oil and gas accumulations are located in
structures that were initiated during the Carboniferous Hercynian
Orogeny. The widespread Hercynian
deformation formed two kinds of structures (1) a broad regional arch oriented
NNE, and (2) narrow north and Northeast trending basement horsts. These uplifts
underwent erosion of pre-Carboniferous rocks, and syntectonic
deposition of the continental Unayzah Formation clastics along their flanks. The Hercynian
Orogeny exerted significant impact on Paleozoic oil
and gas plays. The extent of the Hercynian
deformation and erosion controlled the hydrocarbon accumulations in the
Devonian Jauf, Permo-Carboniferous
Unayzah and Permian Khuff
reservoirs. The Hercynian contributes to the
Paleozoic oil and gas plays by (1) focusing hydrocarbon migration along the
eastern and southern edges of the Central Arabian Arch, (2) providing top and
lateral seals for the Devonian Jauf truncation play
along the edges of Hercynican uplifts where the
Permian Unayzah is absent, and (3) channeling
hydrocarbons through major Hercynian faults. The
reactivation of Hercynian faults during the first and
second Alpine Orogenies developed migration pathways
from the Silurian source rocks to the Upper Paleozoic reservoirs. Furthermore,
in areas where the Hercynian unconformity has eroded
into the Cambro-Ordovician section, the Unayzah reservoir was subjected to high pressure- brines
from the Cambro- Ordovician, which may have displaced
hydrocarbons from these traps.