Asmari Giant Reservoirs

The Discoverer

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The Asmari Giant ReservoirsMore than one century of exploration and production

The Asmari succession is the young-est and most prolific reservoir hori-zon in Iran. This succession produc-es more than 80% of total Iranian crude oil (85% in some estimation and references). In addition, super-giant and giant oil and gas resource are stored in the Formation equiva-lents in the Kirkuk province, Iraq (for example Bai Hassan field). As well as, Asmari Formation hosts gas associated (gas cap) and non-associ-

Fig. 1) First hydrocarbon well in Middle East (Well No. 1 of Masjid Sulaiman) after one century; in 1908. (upper photo from Anglo-Persian Oil Com-pany) and 2011 (lower photo from Mehrnews agency).

The Asmari Formation (Oligo-Mio-cene) is mainly consists of carbonate (limestone and dolomite) but it also has a mixed siliciclastic/carbonate (Ahwaz member; fluvio-deltaic si-liciclastic deposition in Khuzestan) and evapoitic successions (Lur-estan). Ahwaz member and its equiv-

alent (Ghar sandstone) are major oil reservoirs in the west Persian Gulf sub-basin (such as Forouzan, So-roush, Abuzar, Nowruz, and also Ahwaz fields).Many of giant and supergiant fields in Iran have multiple reservoir hori-zons, commonly involving the As-

The Asmari Formation is very interesting for following characteristics and reasons (Fig. 2):

• The presence of extensive fracturing system, with other pore types (high proper m values, 12 % average porosity).

• Shallow depth of burial for low-priced drilling (ranges from 300 to 3300 meters).• High reservoir pressure (Gas-cap). • High quality crude oil with low sulfur content (mean 1.6 %) and light gravity oil (mean API >30°).• Numerous and giant anticlinal structures that act as trap (with economic closure).• The presence of Oil seeps, good indicators for exploration and survey. • The presence of thick and efficient seal rock (Gachsaran evaporate).• The occurrence of extensive organic rich source rocks.• Good position in stratigraphic framework for lateral migration and trapping of hydrocarbon.

ated with oil pools. The Asmari has gas cap with associated oil pool in more than 22 fields of Dezful Em-bayment area. In this area, large amounts of gas in these fields, inject-ed for effective production from ad-jacent old oil fields. The main sand-stone reservoir layers in Iranian fields are hosted in Asmari formation (with “sand production problem”).The Asmari is well-known as typical fractured carbonates reservoirs. Ex-

ploration and production from this most famous oil-producing forma-tion goes back to the last century. In 26 May 1908, D’Arcy and his asso-ciates struck oil from Asmari forma-tion in southwest Iran (Masjid Su-laiman-1 well in Fig. 1). It was the first commercial oil discovery in the Middle East. So, some of the Asmari fields have been in production for nearly a century.

Geography

mari carbonate (such as Agha Jari, Gachsaran, Ahwaz, Mansuri, Lali, Karanj, Masjide- Suleiman, Marun, Par-e-siah, Dehluran, Cheshmeh Khosh, Hendijan, Bibi-Hakimeh and Paydar).

Issue 4 – Autumn 2011

Fig. 2) Fracturing and presence of oil seep are two main characteristics of the Asmari outcrops in Zagros mountains. Fractured system in Kavar, Iran (Left; photo from M. Mirkazemian) and oil seeps (right; photo from M.T. Barin) in Asmari outcrops.

Reservoirs

Some 59 hydrocarbon fields (51 oil and 8 gas reservoirs) are explored from the succession in the Zagros and Persian Gulf Basins (Fig. 3). A majority of the Asmari oil reservoirs are clustered in Dezful Embayment and western Fars and Persian Gulf provinces. Some Asmari gas fields are located in Bandar Abbas Hinter-

land (Sothern-Gashu, Western Salt, Gavarzin gas fields) and in Persian Gulf (Bahregansar, Thundar, Farur A) area. The Milatun and Kuh-e-As-mari are two other Asmari gas fields in the Dezful Embayment. Except of Gavarzin Field, other gas fields are not developed yet. The dominant trend of the fields is parallel to NW-

SE Zagros structural elements. Ap-parently, the absense of Asmari res-ervoirs north of Balarud and Mountain Front Faults in the Lur-estan and Izeh provinces may ex-plain the lack of Asmari Field in these areas.

One-third of the total proven Asmari reservoirs (7 gas and 10 oil fields in offshore and onshore) are not developed (Ta-ble.1). The Naft Shahr, Dehloran and West Paydar Fields are three common Asmari fields that are shared between Iran and Iraq. The Aghajri, Pazanan, Bibi Hakime, Parsi, Labe Sefid, Rage Sefid, Nafte Sefid are examples of Asmari associated gas reservoirs.

Fig. 3) A map showing distribution of Asmari oil and gas reservoirs in the Zagros and Persian Gulf Basins. In general, most of oil reservoirs are clustered in Dezful Embayment and western Fars and Persian Gulf provinces. Three Asmari gas reservoirs are situated in Bandar Abbas Hinterland.

The Discoverer

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AAPG Corporate Group Memberships Offer Many Benefits

In its on-going effort to reach every geoscientist throughout the world, AAPG has created the Corporate Group Membership Program, initiated specicially with National Oil Companies in mind. This program was designed to streamline the membership application process for busy oil and gas industry professionals, while providing excellent cost savings to the sponsoring company.

AAPG Corporate Group Membership offers cost-saving services with discounted fees for Datapages digi-tal archive and discounted prices on AAPG Educational services. In addition, AAPG waives the annual postal surcharge fee, which can save a company with 200 participants $4,000.00. Minimum enrollment for this program within a company is 50 participants.

This program offers simplified billing, with one statement/invoice for all participants, with annual review. The actual cost for enrollment in these programs is based upon the number of memberships enrolled/paid for by the company, along with any relevant products/services offered by AAPG.

For more information please contact: AAPG Member Services Manager, Vicki Beighle [email protected]

Although the Asmari Formation contains very important reservoir intervals, there remain many questions in geological age, depositional environment history (particularly source of the Ahwaz sands), regional controls on reservoir properties, environmental problems involving oil seepage and unconsolidated sand production, for continuing investigations.

Asmari Reservoirs # #

Total reservoirs 59

Proven oil reserves 51

Proven gas reserves 8

Productive fields 42

Productive oil fields 41

Onshore productive oil fields 37

Offshore productive oil fields 4

Productive gas fields 1

Onshore productive gas reservoirs 0

Offshore productive gas reservoirs 1

Undeveloped reservoirs 17

Undeveloped oil reservoirs 11

Undeveloped gas reservoirs 6

Undeveloped onshore reservoirs 10

Undeveloped offshore reservoirs 4

Behrooz Esrafili-Dizaji ([email protected])Farkhondeh Kiani Harchegani ([email protected])

Reservoirs cont’d

Asmari Giant Reservoirs

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