Basin Modeling Study of the Anaran Block, Iran — Pre-Drill Predictions and Post-Drill Results

Balazs Badics¹, Arne Sigurd Steen¹, and James Efstathiou^2
1Hydro Oil & Energy, Research Centre Bergen, Sandsliveien 90, N-5020 Bergen, Norway
phone: ++47-41576257, e-mail: [email protected]
²Hydro Oil & Energy, Global Exploration, Kjørbo, Oslo, Norway

The petroleum system of the Anaran exploration block in Iran was investigated using basin-modeling techniques between 2004 and 2006. The study focused on the potential source rocks, their maturity and timing of hydrocarbon generation. The emphasis of the study was to match the predicted and observed fluid properties in known accumulations, in order to predict hydrocarbon properties in undrilled prospects.

Before drilling the main source rock units were studied in outcrop sections during extensive field work. The thermal and maturity evolution of the area was investigated with PetroMod software package. A detailed 3-D basin model was built using seismic maps as initial input.

The most likely source rock in the area is the Tithonian-Berriasian Garau Formation, which increases in thickness towards the north. The formation is only penetrated by few wells but forms good outcrop sections at Kabir Kuh and Tang-e-Haft. The Albian Kazhdumi Formation forms an organic-lean platform facies under most of the area. The Kazhdumi becomes more basinal again towards the west in Iraq, and towards the southeast in the Paydar area. Additional source rock potential exists in the Cenomanian Ahmadi and Coniacian Surgah shales. Good source rock intervals occur also in the Upper Cretaceous Gurpi and Paleogene Pabdeh Formations, but these are immature in the area.

Modeling results indicate that the maturation of the Garau, Kazhdumi and Ahmadi source rocks started in the Middle Miocene, and peak-oil expulsion occurred between 7 and 4 million years ago (Ma) in the main synclines. The main trap-formation event was during the late Miocene folding and uplift of the Zagros, between 8 and 2 Ma before present. Trap formation was coeval with the main oil charge resulting in large under-saturated oil fields. Hydrocarbon migration modeling, which includes multi-component source rock kinetics and PVT analysis, matched all known fields and their fluid types, and correctly predicted the gas/oil ratio (GOR) and oil gravity (API) of the Azar structure before drilling.

After drilling, extensive geochemical analyses were carried out, which verified the pre-drill predictions. The Pabdeh and Gurpi formations were found to be immature, the section below is oil-mature in the new wells. The main oil charge of the Azar field has been probably sourced from the Garau Formation, with additional early mature oil mixing from the Kazhdumi and Ahmadi Formations.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands