Abstract
Description:

The interpretation study which is presented has been carried out on the Silurian-Khuff Petroleum System, to verify a hydrocarbon dysmigration and redistribution concept which was developed by some authors in the past for the Fars domain.

Considering that the Silurian source rock layers have probably worked in the Qatar-Iran area as well as in North Africa (Tanezzuft formation) and other places in the Middle East platform (Qusaiba formation), we have tried a qualitative and quantitative approach of the timing of this generative system at a more extended mega-regional scale.

Method and Results:

At first we attempted a reconstitution through time of the geometry of the area extending between the Qatar Arch and the Fars area further to the north.

This work has been performed by using the available seismic in house complete data set.

Different seismic horizons were calibrated, picked and mapped at this mega-regional scale, including a rigourous time-depth conversion because of some significant seismic velocities variations.

Isobath and isopach maps were built after this first interpretation phase and used to determine how have evolved the top Khuff geometries at different times and particularly during what we consider as the critical moment of the Silurian-Permian Petroleum System.

Observations:
Structural Geology:

The first observation which was done during this study is that different wells prove an important local erosion during Hercynian time.

This event was responsible for the absence of the Silurian section below the Khuff play on the so called Gavbendi High in the Fars area.

The Silurian Generative System is therefore completely absent in this area and cannot have contributed to a vertically driven hydrocarbon charge system of the Zagros (Fars) present structures.

The second important point for the Fars petroleum potential comes from the observation of the dynamic structural evolution of the domain extending between the present Qatar Arch structural feature and the Fars area, particularely during the Mesozoic.

It appears clearly from calculated isopach maps at reference levels and also from reconstructed balanced cross sections that the Qatar Arch has been a dominant structural axis and probably a remnent structural closure from the Late Jurassic to the Oligocene times.

Petroleum Timing:

The huge structure that was created at these times was probably also charged with gas that could have migrated in the Khuff carbonate intervals, if we refer to the different basin modelling results that demonstrated a Lower Cretaceous gas pulse timing for the Silurian Hot Shales.

At the time of the Zagros surrection, which occurred from the Miocene to Present times, the initially formed hydrocarbon trap closure was deformed and moved to a more southern location because of the onset of the Zagros foreland and trough.

The huge gas accumulation that has probably existed during the Cretaceous-Lower Tertiary periods with a corresponding drainage area of 150,000 square kilometers, may be one of the largest holding tank never seen in the world (25000 TCF of gas), was remobilized to the south resulting in the present North Dome field.

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