Tehran Berkeley’s R&D has been active since 1982. Our first research was on   computer software for marine and offshore projects. For the times being our research are more business oriented with more emphasize on Iran and Middle East. Our Colleagues have presented several papers in international conferences, which you will see the summary of the latest being presented here below.

 IMPORTANCE OF PRIMARY MIGRATION OF HYDROCARBONS IN THE FORMATION OF GIANT OIL AND GAS FIELDS OF PERSIAN GULF GEOSYNCLINORIUM

 BY:  GHOLAM- ALI  MOHAJER^*


 ABSTRACT

Primary migration plays a very important part in the formation of giant oil and gas reserves. Citing, for example, the biggest oil and gas region of the world and investigating its geographical setting, that is, the sedimentary basin of the Persian Gulf during the different geologic periods.

Continuous subsidence and sedimentation from the close of the Paleozoic to late Tertiary has deposited over 10,000 meters of sediments on the northern side of the Persian Gulf namely Lurestan, Khuzestan and Bandar Abbas areas. Isopach maps of different geologic perids of this huge area show the thinnest sedimentary deposits on the Arabian Platform situated on the southern side of the geosynclinorium.

Published proven reserves up to the middle of 1995 is over 677 billion barrels of oil of this, nearly 555 billion barrels or 82% lies on the southern side of the Persian Gulf. And, the proven gas reserve is over 1400 trillion cubic feet, of which nearly 690 trillion cubic feet or 49% is located in Iran.

The Cretaceous isopach map of the region shows the least thickness in the area of Kangan, pirogeny together with salt diapirism persisted in the region from late Jurassic to early Cretaceous times resulting in geologic structures and the rising of salt plugs. These structures with over 1000 meters thickness of the Permian Limestone and dolomite (Khuff Formation) with the anhydride seal have resulted in the prolific accumulation of hydrocarbons.

To date, no commercial gas reserves form exploratory drilling have been discovered on the northern side of the gosyclionorium(Kabir Kuh, Dashtak, Finu). But giant gas fields on the Iranian Platform in the area of kangan, Persain Gulf and part of northern Arabia (Kangan –C, D, F Anticlines in Iranian water; Bahrain, Qatar and Barqan in Arabia) have been discovered.

This is attributed to the huge sedimentary thickness and the resultant over burden pressure on the source rocks on the northern and south eastern side of the geosynclinorium. The organic material was transformed into hydrocarbons and the excessive pressure pushed the generated oil to migrate into the present paleogeographic high structures on the southern side (platform area) and to the north in the Sarvestan and Kuh-e-Rig area.

In the case of gas, however, it migrated towards the Kangan high at the end of the Cretaceous to early Tertiary. This primary migration of hydrocarbons entered the porous limestones and sandstones. According to dunnington the primary migration was responsible for filling all the available pore spaces of the reservoir rocks by the hydrocarbons before compaction and has preserved the primary porosity. Consequently, this primary porosity has with-stood later digenesis and pressures from the overlaying sedimentary cover. This is one of the reasons for the creation of giant oil fields due to the primary migration, I fully agree with this idea.
If we accept primary migration in the formation of giant oil and gas fields the subject of source rock  (in the region of the Persian Gulf and especially the Arabian Peninsula) can  be resolved which has been named in books and periodicals as the extraordinary geological from the presence of mainly continental and evaporitic depositis on the Arabian Perninsula and the large scale shaly and limy favorable source rocks on the northern sides of the geosynclinorium.
For instance, the Silurian carbonaceous shales can be very good source rock for the Permian (Khuff Formation) limestones and dolomite or the Khuff Formation being marly towards the north west of the region can itself be good source rock. The generated hydrocarbons from these source rocks can migrate to the limestone, dolomite and the sandstone reservoirs of the paleogeographic structures to the southern part of the region. Likewise, the khasdhumi, Gadhvan and  Garau shales and marls can be the source rocks for the Burgan sandstone, the Bangestan and the Khami formations respectively. From the above mentioned points it is clear that primary migration has played a very important role in the formation of Khuff gas reserves of the Persian Gulf region, the Jurassic oil reserves of Arabia and the Cretaceous oil of Kuwait, southern Iraq and offshore Persian Gulf.
It should be pointed out that in the Zagros foot-hill structures secondary migration played a more important role in the creation of the prolific Asmari reservoirs from the oil generated in the underlying Pabdeh and Gurpi source rocks by upward migration of oil and gas due to the Alpine Orogeny towards the end of the Pliocene and the formation of huge anticlines in the folded Zagros belt. However, in the high Zagros region, wherever the structures are broken down to the Asmari or the Bangestan and Khami the oil has been destroyed and the remnants are left as asphalt seen in the Asmari or the Bangestan and the Khami fractures.     

* Exploration manager - Tehran Berkeley