Geology Reference
In-Depth Information
The Zagros Foredeep is the richest in the world in terms of the appraised
hydrocarbon reserves and the individual fields belong to the giant and
unique ones. The largest among them are Ahvaz, Marun, Agha-Djari,
Gachsaran and Bibi-Hakime. Most accumulations are found at depth shal-
lower than 2,500 m. The region includes the upper oil-gas and lower gas-
condensate zones.
The following conclusions may be derived by evaluating geology and
hydrocarbon potential of the Alpine folded belts based on general geo-
fluid-dynamic approach:
In the present-day structure, the Alpine fold belts represent the areas
of intense earth crust subsidence with the deposition of thick sedi-
mentary sequences (up to 28
−
30 km).Their tectonics include the fol-
lowing features:
t
Commonality of deep-seated faults.
t
Commonality of step-block structure with sequential subsid-
ence of individual fault-blocks toward centers of depressions and
troughs.
t
Juxtaposition of Stratigraphically and lithologically different inter-
vals across the deep-seated faults.
t
Diversion in structure plans between the competent and incom-
petent complexes.
t
Substantial neotectonic activity.
t
Local structures within individual regions usually form anticlinal
belts (zones) spatially associated with the deep-seated fault areas.
They are usually intensely deformed, often with diapir and mud
volcanoes manifestations.
t
Sedimentary sections in all regions are subjected to lithofacies
rhythmicity, which manifests itself in the periodic replacement in
vertical direction of clay varieties by permeable ones. Very com-
mon are pinch-outs of individual lithological intervals up the
regional dip and down in the direction of folding subsidence.
t
Oil ans gas occurrences in the section are regionally controlled by
the deep-seated faults and their spatial distribution corresponds
with the fault zones. Commercial oil and gas accumulations are
localized in the faulted volumes of traps genetically associated
with the deep-seated faults.
The data of the geologic structure and hydrocarbon occurrence param-
eters for all described Alpine folded belt areas are summarized in Table 1.1.
