Iran's Crude Oil Reserves and Production

GeoArabia, Vol. 12, No. 2, 2007 Iran’s oil reserves and production Gulf PetroLink, Bahrain

Iran’s crude oil reserves and production

Moujahed I. Al-Husseini

ABSTRACT

The Government of Iran estimates the country’s initial-oil-in-place and condensate- in-place are about 600 and 32 billion barrels (Gb), respectively. In 2004, the official estimate of the proved remaining recoverable oil and condensate reserves was about 132.5 Gb, of which crude oil accounted for about 108 Gb. Cumulative crude oil production is expected to cross the 60 Gb mark in 2007, implying that the estimated ultimate recoverable reserves of crude oil are about 168 Gb (cumulative production plus remaining reserves) and the total recovery factor is about 28%. The main Oligocene-Miocene Asmari and Cretaceous Bangestan (Ilam and Sarvak) reservoirs contain about 43% and 25%, respectively, of the total crude oil- in-place. Recovery factors for the Asmari range between about 10–60%, and for the Bangestan between 20–30%. Between 1974 and 2004 remaining recoverable reserves have increased from about 66 to 108 Gb, while the ultimate recoverable reserves have increased from 86 to 168 Gb.

In contrast to 1974 when Iran’s production peaked at 6.0 Mb/d, production in 2005 averaged about 4.1 Mb/d. The 1974 peak occurred when production from most of the giant fields was ramped-up to very high but unsustainable levels. Current plans are to increase the crude oil production rate to 4.6 Mb/d by 2009. This is a significant challenge because this production capacity has to offset a reported total annual decline rate of 300–500,000 barrels/day (Kb/d). This high decline rate is attributed to the maturity of the giant fields, many of which attained their peaks in the 1970s and have produced about half or more of their estimated ultimate recoverable reserves. Therefore to achieve the 2009 production target within the next three years, Iran has to add about 680 Kb/d of capacity per year from its developed fields (infill drilling, recompletions, enhanced and improved oil recovery), while also adding net new surface facilities and well capacity from undeveloped fields and reservoirs.

INTRODUCTION

Iran is a major producer in the Organization of Petroleum Exporting Countries (OPEC) and was one of its founding members when it was formed in 1960. With an average production of about 4.1 million barrels of crude oil per day (Mb/d) in 2005 (Figure 1 and Table 1), Iran supplies approximately 5% of the world’s oil production of 81.1 Mb/d, and 12% of OPEC’s production of 33.8 Mb/d (BP, 2006; quantities include natural gas liquids – NGL and oil from unconventional sources). In mid-2004, the country reported that its proved remaining recoverable crude oil and condensate reserves were about 132.5 billion barrels (Gb) or about 11.3% of the world’s reported proved oil reserves of 1,200 Gb for end-2005 (BP, 2006). The estimated proved remaining crude oil reserves are about 108 Gb, and consist of both primary and secondary reserves (Table 2).

At the June 2006 OPEC meeting in Caracas, Venezuela, Iran’s Petroleum Minister, K. Vaziri-Hamaneh, stated that the country planned to raise oil production to 4.6 Mb/d by 2009 (Middle East Economic Survey - MEES, 5 June 2006). It should be recognized, however, that such an increase represents a significant challenge because it has to overcome a production decline rate in the maturing fields of 300–400,000 (Kb/d) according to former Iranian Petroleum Minister, B. Zanganeh (MEES, 1 August 2005), or as much as 500 Kb/d according to the current Petroleum Minister Vaziri-Hamaneh (MEES, 18 September 2006). The production decline rate is not irreversible and is being overcome with infill drilling, recompletions, enhanced and improved oil recovery (e.g. gas injection programs) in many mature fields. Moreover, to achieve this 12% production capacity expansion, Iran is bringing on- stream several undeveloped fields and reservoirs.

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Iran’s Production History 7

6 80

5 1979 Revolution 60

3 40

1951 Revolution

2 Oil price/barrel (2006 US dollars) Production rate (Million barrel/day)

World War II 20

1 Masjid-e-Sulayman production started (1913) 1980-1988 Iran-Iraq War 0 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2006 Year Figure 1: Iran’s daily production of crude oil from 1913 to end-2006. Also shown is the average price of a barrel of oil in 2006 dollars.

Table 1 lists Iran’s estimated crude oil production capacity by field (Figure 2) for:

• April 2004 (Arab Petroleum Research Centre – APRC, 2005); • end of 2005 (MEES, 13 February 2006); • end of 2010 and end-2015 (assuming current production rates).

The planned production capacity increases are compiled from various sources and assume no delays in completing the projects (MEES, 13 February and 19 June 2006; McDonald, 2006; Petroleum Review, 2006; OPEC website). Production from the undeveloped Azadegan field (260 Kb/d after 2008, McDonald, 2006) and Kushk Hosseinieh field (300 Kb/d after 2008; McDonald, 2006) are shown as completed by 2010. The 100 Kb/d from the Azar field (announced as commercial in 2006, MEES, 19 June 2006) and 300 Kb/d from Yadvaran field (planned for 2012 or later, but may only be 180 Kb/d, Associated Press in Gulf News, 18 February, 2006) are shown in 2015. Also listed in Table 1 are the specific gravities for the oils in API units (as reconciled between various sources including: Beydoun, 1988; Alsharhan and Nairn, 1997; APRC, 2005; MEES, 13 February 2006; McDonald, 2006).

This article reviews the crude oil and condensate reserves (Tables 2 and 3) and oil production capacities in the main fields and reservoirs of Iran (Table 1), and the country’s overall production history (Figure 1). It first clarifies the nomenclature and stratigraphy of Iran’s fields (Figures 3 and 4), and then explains the sources of the database (Tables 1 –16). One objective of this article is to provide a quantitative data base of Iran’s reserves and production that illustrates the relationships between initial-oil-in-place (IOIP), estimated ultimate recoverable reserves (EURR), remaining primary and secondary reserves (PRR, SRR), total remaining reserves (TRR), reserves growth, cumulative production (CP), recovery factor (RF), decline rates and production. A second objective is to show the relative importance of the reserves and production from the Asmari reservoir in Iran’s four supergiant fields (Agha Jari, Ahwaz, Gachsaran and Marun; Figure 2).

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Table 1 Iran’s Crude Oil Production by Field for 2004 to 2015. MAIN CRUDE OIL x 1,000 barrels/day RESERVOIRS OF IRAN Field API Apr-04 end-05 2010 2015 Ab-Teymour 43 43 43 43 32.6° The onshore reservoirs in Iran are Abuzar 200 190 220 220 26.0° named after formations and groups in Agha Jari (Aghajari) 190 200 200 200 34.6° which they occur, as shown in Figure 3 Ahwaz-Asmari 800 700 700 700 32.6° (Stöcklin and Setudehnia, 1972; Szabo Ahwaz-Bangestan 160 155 220 220 25.5° and Kheradpir, 1978; NIOC, 1998). The Azadegan 0 0 260 260 Heavy offshore reservoirs are named after Azar 0 0 0 100 NR either Iranian or Arabian formations Bahregansar 65 65 65 65 29.8° (Figure 4). Alsharhan and Nairn (1997) Balal 40 40 40 40 42.0° provide a comprehensive review of Bibi Hakimeh 150 130 130 130 29.9° the petroleum systems covering the Binak 50 50 50 50 29.9° reservoirs, seals, source rocks and oil Cheshmeh Khosh 37 36 80 80 28.0° types. Chillinger 10 10 10 10 36.6° Darquain 0 50 160 160 38.5° Tables 2 and 3 provide an overview of Dehluran 9 9 25 25 35.5° the distribution of oil and condensate Doroud (Darius) 150 130 220 220 34.0° by field and reservoir, indicating Forouzan (Fereidoon) 35 35 100 100 28.5° a total crude oil in-place (IOIP) of Gachsaran 650 560 560 560 31.1° Haft Kel 40 40 40 40 31.1° about 600 Gb and condensate in-place Hendjian 8 8 8 8 23.0° (ICP) of about 32 Gb. The Asmari Karangan 5 0 0 0 NR and Bangestan reservoirs are found Karanj 125 150 150 150 34.4° in many fields and account for about Kilur Karim 10 0 0 0 NR 260 Gb and 150 Gb, respectively, Kupal 55 60 60 60 32.0° representing approximately 43% and Kushk Hosseinieh 0 0 300 300 Heavy 25% of initial-oil-in-place. The main Lab-e-Safid 40 40 40 40 35.3° reservoirs are briefly discussed in the Mansouri 60 50 100 100 27.5° following sections. Marun (Maroun) 570 520 520 520 33.0° Masjid-e-Sulayman 6 4.5 20 20 40.0° Oligocene-Miocene Asmari Nargesi 50 0 0 0 NR Reservoir Neft-e-Safid 25 25 25 25 44.5° Neft-e-Shar 15 0 0 0 43.0° Nowruz 90 90 90 90 21.0° The Asmari Formation contains the Par-e-Siah 2 0 0 0 31.7° most prolific and productive reservoir, Parsi (Paris/Faris) 200 100 150 150 33.9° holding some 43% of IOIP. Table 4 shows Pazanan 80 70 150 150 35.0° the relative importance of the Asmari Rag-e-Safid 100 190 250 250 28.6° reservoir in those fields having IOIP of Ramin 2 2 2 2 32.9° in excess of one billion barrels. The four Ramshir 30 25 25 25 27.6° supergiant fields, namely Gachsaran, Resalat + Reshadat 60 13 135 135 34.0° Marun, Agha Jari and Ahwaz, contain Salman (Sassan) 85 85 135 135 35.0° about 152 Gb, or 60% of the Asmari- Shadegan 20 45 45 45 35.6° reservoired IOIP, and about 25% of the Shour 5 0 0 0 NR country’s total. Nine more giant fields, Sirri A and E 102 102 102 102 32.0° each containing more than 5 Gb initial- Sirri C and D 25 25 25 25 31.0° oil-in-place, represent another 30% of Soroush (Cyrus) 100 100 100 100 18.0° Asmari-reservoired IOIP; namely Bibi Yadvaran 0 0 0 300 NR Hakimeh, Parsi, Rag-e-Safid, Ramin, Zaregheh 10 0 0 0 12.0° Karanj, Haft Kel, Pazanan, Masjid-e- Total Oil 4,509 4,148 5,555 5,955 Sulayman and Kupal. Crude oil production capacity listed by field as reported for April 2004 (Arab Petroleum Research Centre – APRC, 2005) and end of 2005 (MEES, 13 February 2006). The quantities for 2010 and 2015 include The recovery factor (RF = EURR/IOIP) planned expansions or assume uniform production after 2005 (sources: for the Asmari reservoir varies from MEES, 13 February 2006; McDonald, 2006; OPEC website). Specific 64% in Ahwaz field to 8% in Kilur gravities for the oils in API units are from MEES (13 February 2006) field (Table 4). Very high recovery except for: Azadegan and Kushk Hosseinieh reported as “heavy” (less than 26° API) by McDonald (2006); Agha Jari, Hendjian, Gachsaran, factors are also noted in Agha Jari (58% Marun, Neft-e-Shar, Nowruz, Par-e-Siah and Zaregheh by Beydoun (1988) and APRC (2005).

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Al-Husseini

26°N 27°N 25°N 22°N 24°N

58°E 57°E 56°E 55°E 54°E 23°N 53°E 52°E OMAN

200 28°N 1 Dubai UAE 1 HD 58°E Khuzestan,

22°N

Hengam Bandar-e-'Abbas Sar Khoon N km Sirri

51°E restan, D Suru Mobarak C

Lu 29°N A of 0 Sirri 57°E Salman Gavarzin Resalat (Rakhsh)

Bastak Namak West Gashu South 23°N

E Salakh (Qeshm) Alpha 50° Sea Arabian provinces Tabnak

Balal 30°N Assaluyeh 3H-2 Varvavi the Shanul QATAR

56°E Doha Bandubast

Kangan of 24°N Pars South Coastal Fars Homa

Nar 49°E Taheri Aghar Bandar

Ghawar

Daryaie 31°N Sarvestan G3 Gardan F-Structure BAHRAIN Zireh Pars North formations 55°E Dalan

Manama 25°N advaran fields are not shown. and Saadat Abad Kuh-e-Mond B-Structure

Bushgan 48°E

Kuh-e-Kaki

Sulabedar Khesht Milatun Rudak Chahar Bisheh 32°N Bushire Nargesi Bushco groups Shiraz Kharj Island Hasbah 54°E Golkhari

SAUDI ARABIA

Doroud Forouzan Shur 26°N Chillinger Mokhtar Siah Makan Bibi Hakimeh Garangan Binak Kilur Karim Interior Fars Esfandiar

Soroush 47°E 33°N Bahregansar Hendijan Rag-e-Safid stratigraphic

Zaqeh Gachsaran

IRAN 500 500

53°E Abuzar , Kushk Hosseinieh and Y Location Map of Iran The Khaviz

Pazanan Nowruz 27°N Mansurabad Kheir Abad Bandar-e- Mahshahr Shuroum Kuwait City Agha Jari

46°E Iran. Bangestan Dudrou Parsi

Kuh-e-Rig 34°N in Marun Ramshir Mamatain

E Darquain 52° Karanj Kilometers KUWAIT Shadegan

Siba Mansouri 28°N Sarajeh Ab-Teymour Zeloi 45°E refineries Ahwaz Lali Kupal Karoon

Jufeyr

Haft Kel 35°N Paydar Susangerd and Papileh Neft-e-Safid Par-e-Siah Khuzestan

51°E Shakeh

Alborz Ramin (Mulla Sani)

0 0 Azadegan Masjid-e-Sulayman 29°N fields

Huwaiza Kabud

30°N Dalpari 31°N 44°E gas

Danan 36°N Haloosh Palangan Dehluran Qaleh Nar N and 300 Lab-e-Safid Lurestan

Cheshmeh Khosh N OMA 50°E km 0 Arabian Sea oil

Samand 32°N UA of QATAR IRAN BAHRAIN Sea Velzenhar Badrah

IRAQ f

Caspian Arabian

Gul 43°EYEMEN d Huleylan Sarkan d

SAUDI ARABIA 37°N Maleh Kuh

KUWAIT Tang-e-Bijar Oil fiel Gas fiel Refinery d Kabirkuh Location 49°E IRAQ Legend Shiel Arabian Neft-e-Shar

Baghdad 2: d 33°N Sea Re N

SYRIA N JORDA TURKEY ERITREA N 42°E

E d

37° 36°N 35°N 34°N Sea Me

48°E 47°E 46°E 45° 44°E 43°E SUDA EGYPT Figure Interior and Coastal Fars are shown in Figure 3. Locations of Azar

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Stratigraphy of Iran

Period Epoch/ Lurestan Khuzestan Coastal Fars Interior Fars Era Pliocene Bakhtyari Lahbari Lahbari Agha Jari Agha Jari FARS GROUP Mishan Miocene Gachsaran Guri Asmari Kalhur Ahwaz Razak Oligocene Asmari Upper Shahbazan Middle Jahrum Pabdeh Pabdeh Pabdeh Jahrum Eocene Lower Kashkan Aleh Zang CENOZOIC (TERTIARY) Paleocene Gurpi Amiran Sachun Maastrichtian Emam Hasan Tarbur Lopha Gurpi Campanian

Upper Santonian Ilam Ilam Senonian Coniacian Surgah BANGESTAN GROUP Turonian Sarvak Ahmadi Sarvak Cenomanian Mauddud

Middle Garau Kazhdumi CRETACEOUS Dariyan Aptian Gadvan Gadvan Fahliyan

Lower Neocomian Fahliyan Garau Hith Gotnia Gotnia Upper KHAMI GROUP Najmah Najmah Surmeh Surmeh Middle Sargelu Sargelu

Alan Alan

JURASSIC Mus MusAdaiyah Adaiyah Lower Neyriz Neyriz

Dashtak Khaneh Kat TRIASSIC Dashtak Aghar Kangan Kangan

Nar PERMIAN Dalan DEH RAM GROUP Chatishen Faraghan

CARBONIFEROUS DEVONIAN SILURIAN Gahkum ORDOVICIAN Zardkuh Zardkuh Zardkuh Ilebeyk Upper C B Middle Mila A

CAMBRIAN Lower Lalun Zaigun UPPER Barut PROTEROZOIC Hormuz

Limestone Shaly Limestone Dolomite Shale Sandstone Anhydrite Shaly Anhydrite Salt Figure 3: Stratigraphy and petroleum systems of Southwest Onshore Iran (after Stöcklin and Setudehnia, 1972; Szabo and Kheradpir, 1978; Ala et al., 1980; and National Iran Oil Company, 1998). The four provinces Lurestan, Khuzestan, Coastal and Interior Fars are shown in Figure 2.

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Table 2 EURR IOIP Field Reservoir IOIP IOIP EURR EURR PRRSRR TRRCP RF Prod Prod Iran’s official estimates in million barrels of crude oil Initial-Oil-In-Place (IOIP), Estimated 1999 2002 1999 2002 1999 1999 1999 1999 % 1999 1999 Ultimate Recoverable Reserves (EURR), Primary, Secondary and Total Remaining Reserves Kushk NR NR NR NR NR NR NR NR NR NR NR NR (PRR, SRR, TRR), Cumulative Production (CP), Recovery Factor (RF in %), EURR Produced Hosseinieh (EURR Prod in %) and IOIP Produced (IOIP Prod in %). Lab-e-Safid Asmari 1,556.0 1,556.0 462.0 508.0 170.4 69.3 239.7 222.3 32.6 43.8 16.8 Lali Bangestan 736.5 2,465.5 32.5 153.5 NRNR 50.0 NC 6.2 NC NC EURR IOIP Maleh Kuh Bangestan 1,331.0 NR NR NR 132.7 0.0 132.7 NCNCNCNC IOIP IOIP EURR EURR PRRSRR TRRCPRF Prod Prod Field Reservoir Asmari 2,499.0 3,731.5 778.0 1,747.1 516.7 0.0 516.7 261.3 46.8 15.0 7.0 1999 2002 1999 2002 1999 1999 1999 1999 % 1999 1999 Ilam 2,443.5 NR NR NR 199.2 50.7 249.9 NC NC NC NC Ilam 7,934.0 NR NR NR 697.4 171.9 869.3 NCNCNCNC Mansouri Upper Sarvak 6,816.5 NR NR NR 585.0 140.6 725.6 NCNCNCNC Ab-Teymour Sarvak 7,983.5 NR NR NR 703.9 172.8 876.7 NCNCNCNC Lower Sarvak 9,271.0 NR NR NR 784.5 193.3 977.8 NCNCNCNC Ilam + Sarvak 15,917.5 8,965.5 1,859.7 2,600.0 1,401.3 344.7 1,746.0 113.7 29.0 4.4 1.3 Ilam + Sarvak 18,531.0 18,531.0 2,075.1 3,259.5 1,568.7 384.6 1,953.3 121.8 17.6 3.7 0.1 Ghar 3,275.0 3,275.0 1,046.0 1,197.0 663.2 0.0 663.2 382.8 36.5 32.0 11.7 Abuzar Asmari 46,665.0 46,665.0 15,996.0 21,962.0 5,322.6 2,654.0 7,976.6 8,019.4 47.1 36.5 17.2 Asmari 893.0 893.0 134.5 134.5 134.5 0.0 134.5 0.0 15.1 0.0 0.0 Marun Bangestan 3,057.5 NR NR NR 177.8 53.0 230.8 NC NC NC NC Asmari 27,942.0 NR NR NR 1,502.4 NRNRNCNCNCNC M-e-Sulayman Asmari and Pabdeh 6,628.0 6,628.0 1,169.0 1,329.0 NRNR 50.0 NC 20.1 NCNC Agha Jari Bangestan 2,260.0 NR NR NR 115.5 NRNRNCNCNCNC Nargesi Asmari + Jahrum 2,044.0 NR NR NR 316.5 74.1 390.6 NC NC NC NC Asmari + Bangestan 30,202.0 30,202.0 15,611.0 17,377.0 1,617.9 5,085.0 6,702.9 8,908.1 57.5 51.3 29.5 Asmari 2,388.0 NR NR NR NR NR NR NC NC NC NC Asmari 27,914.0 27,913.0 14,335.5 17,922.8 6,169.3 0.0 6,169.3 8,166.2 64.2 45.6 29.3 Bangestan 599.0 NR NR NR NR NR NR NC NC NC NC Ilam 12,802.0 12,802.0 NR NR 1,521.7 357.9 1,879.6 NCNCNCNC Neft-e-Safid Asmari + Sarvak 24,753.0 24,753.0 NR NR 2,200.5 626.9 2,827.4 NCNCNCNC 2,987.0 3,118.2 485.5 667.1 NRNR 38.8 446.7 21.4 67 14.3 Ahwaz Bangestan Ilam + Sarvak 37,555.0 37,555.0 5,313.3 7,667.9 3,722.2 984.8 4,707.0 606.3 20.4 7.9 1.6 Nahr-e-Umr 2,020.0 2,555.7 767.0 971.2 658.9 0.0 658.9 108.1 38.0 11.1 4.2 Khami 486.0 486.0 93.3 93.3 76.0 17.3 93.3 0.0 19.2 0.0 0.0 Shu'aiba 500.0 500.0 100.3 100.3 100.3 0.0 100.3 0.0 20.1 0.0 0.0 Gurpi 1,560.0 1,560.0 191.5 191.5 156.0 35.5 191.5 0.0 12.3 0.0 0.0 Nowruz Dictioconous + Sarvak 22,271.0 22,271.0 4,099.9 4,099.9 3,340.0 759.9 4,099.9 0.0 18.4 0.0 0.0 147.0 902.0 14.7 107.7 NR NR NR NC NC NC NC Azadegan Yamama Kazhdumi 560.0 560.0 68.7 68.7 56.0 12.7 68.7 0.0 12.3 0.0 0.0 Mishrif, Sarvak + Gadvan 710.0 710.0 200.1 200.1 163.0 37.1 200.1 0.0 28.2 0.0 0.0 Nosrat 192.0 192.0 80.2 96.0 54.0 0.0 54.0 26.2 50.0 27.3 13.6 Fahliyan Azar* NR NR 2,000.0 NR 400.0 NRNR 400.0 0.0 20.0 0.0 0.0 Parsi Asmari 12,292.5 12,650.8 3,289.0 3,811.2 1,199.3 680.0 1,879.3 1,409.7 30.1 37.0 11.1 Ghar 256 NR NR NR 81.0 0.0 81.0 NCNCNCNC Paydar Asmari 939.0 NR NR NR 113.7 0.0 113.7 NCNCNCNC Bahregansar Asmari A 28.0 NR NR NR 0.0 0.0 0.0 NCNCNCNC Pazanan Asmari 6,929.0 7,555.0 879.0 1,854.6 NRNR 225.6 653.4 24.5 35.0 8.6 Sarvak 390.0 360.5 105.5 187.5 NRNR <50 NC NC NC NC Balal Hith + Arab 530.0 530.0 167.1 167.1 111.4 55.7 167.1 0.0 31.5 0.0 0.0 Asmari 12,068.5 12,068.5 NR NR 1,627.7 0.0 1,627.7 NCNCNCNC Asmari 14,890.0 NR NR NR 692.6 NRNRNCNCNCNC Rag-e-Safid Bangestan 6,674.5 6,674.5 NR NR 891.0 0.0 891.0 NCNCNCNC Bibi Hakimeh Bangestan 2,142.0 NR NR NR 74.0 NR NR NC NC NC NC Asmari + Bangestan 18,743.0 18,743.0 3,975.5 4,995.5 2,518.7 0.0 2,518.7 1,456.8 26.7 29.1 7.8 Asmari + Bangestan 17,032.0 17,032.0 3,851.5 5,670.6 766.6 792.9 1,559.5 2,292.0 33.3 40.4 13.5 Ramin* Asmari 1,905.0 5,700.0 NR NR ** 855.0 NCNCNCNC Binak Bangestan 3,280.0 3,511.0 940.0 1,012.0 226.1 341.0 567.1 372.9 28.8 36.8 10.6 Asmari 1,762.5 1,762.5 397.1 591.7 179.6 73.6 253.2 143.9 33.6 24.3 8.1 Ramshir Changuleh Dariyan + Sarvak 944.0 944.0 173.8 173.8 141.6 32.2 173.8 0.0 18.4 0.0 0.0 Bangestan 480.5 NR NR NR 56.7 13.1 69.8 NC NC NC NC Cheshmeh K. Asmari 2,075.5 2,255.0 494.1 840.0 256.8 91.6 348.4 145.7 37.3 17.3 6.5 Shu'aiba 703.6 NR NR NR 76.3 20.6 96.9 NC NC NC NC Dariyan + Fahliyan 992.5 NR NR NR 97.5 23.1 120.6 NCNCNCNC Resalat Chillinger Arab C 756.7 NR NR NR 131.8 15.9 147.7 NC NC NC NC Surmeh 1,184.5 NR NR NR 79.0 27.9 106.9 NCNCNCNC Reshadat Mishrif 600.3 NR NR NR 93.4 0.0 93.4 NCNCNCNC Asmari 1,061.0 NR NR NR 91.7 22.3 114.0 NCNCNCNC (Rostam) Shu'aiba 2,458.5 NR NR NR 118.9 295.0 413.9 NCNCNCNC Danan Bangestan 2,195.5 NR NR NR 134.8 30.7 165.6 NC NC NC NC Rig Dariyan 404.0 404.0 155.9 155.9 127.0 28.9 155.9 0.0 38.6 0.0 0.0 Sarvak 707.5 707.5 130.2 130.2 106.1 24.1 130.2 0.0 18.4 0.0 0.0 Rudak Khalij + Fahliyan 670.0 670.0 109.3 109.3 89.0 20.3 109.3 0.0 16.3 0.0 0.0 Darquain Fahliyan 3,497.0 6,507.0 437.6 2,642.0 356.5 81.1 437.6 0.0 40.6 0.0 0.0 Buwaib 538.0 NR NR NR 87.9 192.0 279.9 NC NC NC NC Dehluran Sarvak 4,401.7 NR NR NR 628.8 150.5 779.3 NCNCNCNC Salman Upper Arab 1,662.5 NR NR NR 359.7 90.2 449.9 NC NC NC NC Yamama, Manifa 6,773.0 10,797.3 3,222.0 3,409.8 1,171.0 933.0 2,104.0 1,118.0 31.6 32.8 10.4 Lower Arab 2,533.5 NR NR NR 331.8 0.0 331.8 NCNCNCNC Doroud Ratawi 3,307.0 3,307.0 329.0 329.0 329.0 0.0 329.0 0.0 9.9 0.0 0.0 Sarkan Bangestan 1,146.0 NR NR NR 50.1 12.7 62.8 NC NC NC NC Esfandiar Lower Ratawi 532.0 532.0 169.7 169.7 169.7 0.0 169.7 0.0 31.9 0.0 0.0 Sarvestan Bangestan 1,021.5 1,021.5 203.8 203.8 166.0 37.8 203.8 0.0 20.0 0.0 0.0 Ferdous L. Cretaceous + Arab 30,610.0 30,610.0 3,061.0 3,061.0 0.0 3,061.0 3,061.0 0.0 10.0 0.0 0.0 Upper Asmari 1,376.0 NR NR NR 338.0 95.2 433.2 NCNCNCNC Shadegan Burgan A +B 511.0 NRNRNR 74.9 0.0 74.9 NC NC NC NC Lower Asmari 1,722.5 NR NR NR 265.8 82.0 347.8 NC NC NC NC Burgan C + D 903.0 NR NR NR 175.1 0.0 175.1 NCNCNCNC Shoroum Sarvak 984.0 984.0 229.5 229.5 187.0 42.5 229.5 0.0 23.3 0.0 0.0 Foroozan Shu'aiba 378.0 NR NR NR 70.7 0.0 70.7 NCNCNCNC Siah Makan Bangestan 1,338.0 1,338.0 83.5 83.5 68.0 15.5 83.5 0.0 6.2 0.0 0.0 All formations? 2,495.0 3,095.4 938.5 1,067.6 NRNRNRNCNCNCNC Sirri A Ilam 2,383.0 NR NR NR 53.0 0.0 53.0 NCNCNCNC Asmari 49,342.5 49,342.5 NR NR NR NR NR NC NC NC NC Sirri C Mishrif 551.0 NR NR NR 41.9 55.2 97.1 NC NC NC NC Bangestan 3,617.5 3,617.5 NR NR NR NR NR NC NC NC NC Sirri D Mishrif 728.0 NR NR NR 173.3 39.1 212.4 NC NC NC NC Gachsaran Asmari + Bangestan 52,960.0 52,960.0 14,561.5 16,246.5 4,166.2 2,232.7 6,398.9 8,162.6 30.7 50.2 15.4 Sirri E Mishrif 2,267.0 NR NR NR 176.8 739.9 916.7 NCNCNCNC Khami 438.0 NR NR NR 69.0 15.9 84.9 NC NC NC NC Burgan A 3,020.0 NR NR NR NR NR NR NC NC NC NC Ghalehnar Asmari 1,915.0 2,597.4 230.2 464.5 161.7 42.7 204.4 25.8 17.9 5.6 1.0 Burgan B 6,902.0 NR NR NR NR NR NR NC NC NC NC Golkhari Asmari + Jahrum 1,770.5 NR NR NR 104.1 28.7 132.8 NC NC NC NC Burgan A + B 9,922.0 9,878.8 598.0 1,327.4 536.0 0.0 536.0 62.0 13.4 4.6 0.6 Soroush Haft Kel Asmari 8,575.0 8,575.0 1,926.0 1,946.0 NRNR 50.0 1,876.0 22.7 96.4 21.8 Burgan C 1,838.0 1,838.0 81.9 81.9 0.0 81.9 81.9 0.0 4.5 0.0 0.0 Jufeyr Bangestan 3,524.0 3,524.0 169.4 169.4 138.0 31.4 169.4 0.0 4.8 0.0 0.0 Dictioconous + 3,362.2 3,362.2 293.0 293.0 NR 293.0 293.0 0.0 8.6 0.0 0.0 Asmari 8,822.5 NR NR NR 1,750.0 NRNRNCNCNCNC Yamama Karanj Pabdeh 1,583.0 NR NR NR 351.0 NRNRNCNCNCNC South Pars Dariyan C 6,005.00 6,005.00 1,313.00 1,313.00 340 973 1,313.00 0 21.9 0 0 Asmari + Pabdeh 10,405.5 11,167.6 4,578.0 5,731.5 2,101.0 822.8 2,923.8 1,654.2 51.3 28.9 14.8 Sulabedar Khami 1,749.5 NR NR NR 159.4 36.7 196.1 NC NC NC NC Karoon Asmari 1,171.0 NR NR NR 64.7 17.4 82.1 NC NC NC NC West Paydar Bangestan 2,778.5 NR NR NR 292.8 67.3 360.1 NC NC NC NC Khaviz Dariyan + Gadvan 1,949.0 1,949.0 197.6 197.6 161.0 36.6 197.6 0.0 10.1 0.0 0.0 Yadvaran NR NR NR NR 3,000.0 NRNRNR 0.0 NC NC NC Khesht Asmari + Jahrum 902.2 902.2 197.0 197.0 160.5 36.5 197.0 0.0 21.8 0.0 0.0 Zagheh Pabdeh 1,729.0 NR NR NR 273.5 0.0 273.5 NCNCNCNC Asmari 3,385.0 3,385.0 263.9 263.9 215.0 48.9 263.9 0.0 7.8 0.0 0.0 Zilaee Asmari 2,652.5 2,652.5 500.8 940.8 402.1 92.8 494.9 59.0 35.5 6.2 2.2 Kilur Bangestan 1,088.0 1,088.0 67.5 67.5 55.0 12.5 67.5 0.0 6.2 0.0 0.0 < 50 million Onshore developed 20,637.1 NR NR NR 347.9 169.9 522.3 NCNCNCNC Kuh-e-Kaki Bangestan 953.0 953.0 98.2 98.2 80.0 18.2 98.2 0.0 10.3 0.0 0.0 < 50 million Onshore undeveloped 5,081.3 NR NR NR 428.3 97.5 525.8 NC NC NC NC Jahrum 4,037.0 4,037.0 404.0 404.0 0.0 404.0 404.0 0.0 10.0 0.0 0.0 < 50 million Offshore developed 2,999.3 NR NR NR 320.8 0.0 320.8 NCNCNCNC Kuh-e-Mond Sarvak 4,813.0 4,813.0 960.0 960.0 240.0 720.0 960.0 0.0 19.9 0.0 0.0 < 50 million Offshore undeveloped 1,392.9 NR NR NR 129.7 0.0 129.7 NCNCNCNC Asmari 5,918.0 5,918.0 NR NR 438.2 198.0 636.2 NCNCNCNC Note: Row 2 is the year reported. NR = not reported, NC = not calculated. Azar, Kush Hosseinieh and Yadvaran fields were not Kupal Bangestan 4,300.5 4,300.5 NR NR 389.4 100.0 489.4 NC NC NC NC included in Iran’s 2002 reports to OPEC. Yadvaran EURR estimated at 3.0 Gb in trade literature. The quantities shown for Asmari + Bangestan 10,218.5 10,218.5 1,493.5 2,131.8 827.6 298.0 1,125.6 367.9 20.9 17.3 3.6 Ramin were updated by Iran from those reported in 2002.

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including the Bangestan reservoir), Marun and Mansouri (47%) fields. High recovery factors (30–40%) characterize the Cheshmeh-Kosh, Gachsaran, Lab-e-Safid, Parsi and Ramshir. Recovery factors of less than 30% are found in the Abu Zar, Ghalehnar, Haft Kel, Masjid-e-Sulayman and Pazanan fields.

According to Alsharhan and Nairn (1997), the Asmari Formation in the Khuzestan Province (Figure 2) consists of wackestone and packstone, ranging in thickness from 320–488 m (1,050–1,600 ft), of which 10–280 m (33–918 ft) comprise effective reservoirs. Evaporites of the Gachsaran Formation provide an overlying seal (Figures 3 and 4). The reservoir generally has a low primary porosity of less than 5%; but as much as 25% secondary porosity due to fracturing. The average permeability is about 10 mD but can reach 100 mD in fractured zones.

To the north of the Gulf, the Ahwaz Formation contains sandstone layers that significantly improve the porosity, permeability and recovery factor. The improvement is well illustrated by the very high recovery factor of 64% for the Asmari sandy reservoir in Ahwaz field (Table 4), which is made up of eight sandstone and six carbonate layers (Schlumberger, 2003). The production (700–800 Kb/d, Table 1) comes mainly from 200 wells producing from the Asmari sandstone layers, which have a high porosity and permeability and act as conduits for fluid flow. The Asmari carbonates, by contrast, have low porosity and permeability and act as barriers. The Asmari reservoir in Marun field also contains sandstone layers (Beydoun, 1988) and has a high recovery factor of 47%.

Cretaceous Bangestan Reservoir

The second most prolific and productive zone is the Cretaceous Bangestan Reservoir (Table 2). It is found in two formations that sometimes contain separate reservoirs. The older Sarvak reservoir is found in the Albian-Turonian Sarvak Formation (= Arabian Wasia Group, Figure 4). The younger Ilam reservoir is found in the Santonian-Campanian Ilam Formation (= lower part of the Arabian Aruma Formation or sometimes Aruma Group, Figure 4).

A number of confusing issues of nomenclature are to be noted. The Bangestan Reservoir should not be confused with the Albian-Campanian Bangestan Group consisting of the Kazhdumi, Sarvak, Surgah and Ilam formations (Figure 3). In some fields, the Kazhdumi Formation consists of sandstones and is separately reported as a reservoir by this name although it is part of the Bangestan Group. In other fields, the Kazhdumi is replaced by the correlative Burgan reservoir of Iraq and Kuwait, the Khafji and Safaniya reservoirs of Saudi Arabia and the Nahr Umr (Nahr-e-Umr) reservoir of Oman (Figure 4).

The Bangestan reservoir contains large amounts of initial-oil-in-place in several of the fields listed in Table 2. In general, the recovery factors range between 20% and 30%. The Ahwaz field has the largest amount of initial-oil-in-place at about 37.6 Gb, with a recovery factor of 20%, being followed by Azadegan (22.3 Bb, 18.4%), Mansouri (18.5 Bb, 17.6%) and Ab-Teymour (9.0 Gb, 29%). But the Bangestan reservoir is not as prolific as the Asmari reservoir in the supergiant Agha Jari and Marun fields, containing about 2.3 Gb and 3.0 Gb, respectively.

According to Alsharhan and Nairn (1997), the Bangestan reservoir consists of massive, shallow- marine limestones. The gross and net thickness range of the reservoir are 220–980 m (722–3,214 ft) and 70–630 m (230–2,066 ft). The Bangestan reservoir has a porosity range of 4–15%. The older Sarvak Formation consists of a lower argillaceous limestone, grading upwards into massive microporous limestone and nodular chert. The porosity of between 7–14% is due to fissuring, and the gross and net thickness range from 24–790 m (79–2,591 ft) and 5–285 m (16–935 ft). The Ilam Formation consists of argillaceous limestone and shale with porosity of 9–20%, also due to fissuring, while gross and net thicknesses range from 25–170 m (82–558 ft) and about 110 m (361 ft), respectively.

OTHER RESERVOIRS

Numerous other less prolific reservoirs are listed in Tables 2 and 3, and are described by Alsharhan and Nairn (1997). Only a few additional comments are called for.

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Stratigraphy of the Gulf

North West South East Epoch/Era Tectonics Gulf Gulf Gulf Gulf

QUATERNARY Bakhtiari Zagros Kharj Pliocene Dibdibba Agha Jari Mountains Hotuf FARS Lower Fars GROUP Mishan Y) Miocene Dam Gacharsan 2nd Alpine Ghar Event Hadrukhi Asmari Oligocene CENOZOIC (TERTIAR Dammam Eocene Rus Pabdeh Neo-Tethys Paleocene Umm Er Radhuma Closure

Maastrichtian Tayarat Simsima Gurpi Fiqa Campanian Bahra Aruma Oman Obduction Upper Santonian Halul Ilam Gudair 1st Alpine Event Coniacian Laffan Mishrif Mbr Turonian Magwa Rumaila Mbr Mishrif Ahmadi Mbr Sarvak Cenomanian Ahmadi Wara Wara Mbr Shilaif (Khatiyah) ACEOUS Middle Mauddud Mbr

Mauddud Mauddud BANGESTAN GROUP Albian

Safaniya Mbr WASIA GROUP Burgan Khafji Mbr Nahr Umr Kazhdumi CRET Aptian Shu'aiba Bab Mbr Shu'aiba Shu'aiba Dariyan Biyadh Barremian Zubair Kharaib Lekhwair Buwaib Gadvan Hauterivian Zakum Mbr

Lower Ratawi Valanginian Yamama Habshan Fahliyan Minagish Berriasian Sulaiy THAMAMA GROUP

Hith P 1st Anh - Salt Hith Arab A Neo-Tethys Tithonian 2nd Anh - Salt Realm Arab B Asab 3rd Anh - Salt

Arab C KHAMI GROU

Upper 4th Anh - Salt Arab D Surmeh Kimmeridgian Jubaila Diyab Hanifa Oxfordian Najmah Tuwaiq Mt. Araej Sargelu Callovian Dhruma Uwainat JURASSIC Bathonian Araej Dhruma Dhruma Izhara Middle Bajocian Aalenian Toarcian Marrat Izhara Neyriz Pliensbachian Lower - Hettangian Upper Minjur Hamlah Middle Jilh Gulailah SIC Dashtak Zagros Rift

TRIAS- Lower Sudair Sudair Kangan UPPER PERMIAN Khuff Khuff Dalan Figure 4: Simplified tectono-stratigraphy and Limestone Grainstone Dolomite petroleum systems of the Gulf. North Gulf Packstone corresponds to Kuwait and southeast Iraq, West Argillaceous Dolomitic Sandstone Gulf to Bahrain and Saudi Arabia, South Gulf to Limestone Limestone Qatar and the United Arab Emirates, and East Gulf Marly Shale Oil Gas to offshore Iran. Limestone

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Table 3 The Ghar Formation is a lateral Iran’s Initial-Condensate-In-Place (ICP), Total Recoverable equivalent of the Asmari Formation Reserves (TRR) and Recovery Factor (RF) (million barrel). (Alsharhan and Nairn, 1997) and ICP TRR RF contains oil in, for example, Abuzar Field Reservoir 1999 EURR % and Bahrengansar fields. The Guri Agha Jari Khalij 37.6 30.3 80.6 and Razak formations also partly Aghar Dashtak + Deh Ram 130.9 107.2 81.9 correlate with the Asmari Formation. Upper Dalan - Kangan 40.6 29.5 72.7 Assaluyeh The underlying Paleocene-Eocene Lower Dalan 4.4 3.2 72.7 Babaghir Ilam 18.8 13.0 69.1 Jahrum and Pabdeh formations also Bahregansar Ghar 50.5 42.7 84.6 locally contain reservoirs (Figure 3, Balal Deh Ram 3.4 2.2 64.7 Tables 2 and 3). Gadvan 31.7 21.1 66.6 Bibi Hakimeh Fahliyan 272.8 196.8 72.1 Dalan Dashtak + Deh Ram 145.1 103.6 71.4 The youngest Cretaceous reservoir Sargelu 1.8 1.3 72.2 in Iran is found in the Maastrichtian Darquain Alan + Mus 2.1 1.5 71.4 Gurpi Formation, and it is deve- Farsi-B Deh Ram 256.0 204.8 80.0 loped as a separate reservoir in, Ferdous Deh Ram NR NR for example, Azadegan field. Gardan Upper Dalan + Kangan 25.9 19.9 76.8 Ghalehnar Pabdeh + Bangestan NR NR Below the Gurpi Formation, the Dalan + Kangan 222.0 180.0 81.1 undifferentitated Khami reservoir Golshan Lower Dalan 320.0 265.0 82.8 takes its name after the Jurassic- Faraghan 136.5 112.0 82.1 Lower Cretaceous Khami Group Haloosh Ilam NR NR Hengam Ilam + Sarvak 229.0 153.0 (Figures 3 and 4). In most fields Kabirkuh Deh Ram NR NR however the individual reservoirs Kamankuh Sarvak 61.2 42.9 70.1 of this age are cited separately (in Kangan Upper Dalan + Kangan 391.8 251.5 64.2 alphabetical order: Arab, Dariyan Karoon Bangestan 58.7 45.6 77.7 Kheir Abad Gadvan NR NR or Darivan, Fahliyan, Gadvan, Hith, Kuh-e-Mond Upper Dalan + Kangan NR NR Manifa, Ratawi, Shu’aiba, Surmeh, Asmari 23.8 19.0 79.8 Thamama and Yamama). The so- Milaton Khalij 5.2 4.2 80.8 called “Dictioconous” reservoir Surmeh 112.7 90.2 80.0 of the Nowruz field has not been Mobarak Thamama 101.0 15.2 15.0 Kazhdumi + Darivan 79.0 42.7 54.1 described in the literature but is Mokhtar Gadvan 13.9 7.5 54.0 probably of Early Cretaceous age. Nar Upper Deh Ram 123.7 81.4 65.8 The Khalij reservoir, which contains Upper Deh Ram 232.0 184.5 79.5 North Pars condensate reserves in the Agha Jari Lower Deh Ram 31.0 26.0 83.9 Asmari 4,142.0 2,546.0 61.5 and Milaton fields, has also not been Pazanan Khami 227.4 157.7 69.3 described in the literature but is Rag-e-Safid Fahliyan NR NR probably of middle Cretaceous age. Reshadat Deh Ram 94.4 70.4 74.6 Ilam + Sarvak 31.2 22.1 70.8 Salakh Most of the gas and condensate Khami 7.2 5.1 70.8 Salman Deh Ram 153.0 122.1 79.8 reserves (Table 3) are found in the Samand Upper Dalan NR NR Permian-Triassic Deh Ram (Dehram) Guri 165.0 120.4 73.0 Sarkhoon Group. In ascending order, it Jahrum + Razak 170.7 126.7 74.2 comprises the Faraghan clastics Dashtak + Upper Kangan 56.4 42.6 75.5 Shanul Upper Dalan + Kangan 70.6 53.8 76.2 and Dalan carbonates/evaporites Asmari NR NR of the Permian, and the Kangan Pabdeh NR NR South Gashou carbonates of the Lower Triassic. Sarvak 25.4 18.9 74.4 The Upper Dalan Member (above Khami 44.7 32.4 72.5 the middle Nar Anhydrite Member) South Pars Deh Ram 22,192.0 14,400.0 64.9 South Pars LPG Dalan + Kangan (C1+C3) 3,196.00 and Kangan Formation represent Suru Khami 17.9 14.3 79.9 the most significant reservoirs for Tabnak Deh Ram + Dashtak 544.7 392.8 72.1 non-associated gas and condensate, Tang-e-Bijar Sarvak 93.9 65.6 69.9 being correlative with the Khuff A, Varvavi Deh Ram + Dashtak 11.8 9.6 81.4 Velzenhar Sarvak 36.1 27.2 75.3 B and C reservoirs of Saudi Arabia West Namak Asmari + Jahrum 12.4 8.7 70.2 (Alsharhan, 2006; Insalaco et al., Zireh Dashtak + Upper Dalan 2.8 2.1 75.0 2006). In some fields, the Triassic < 50 Million Onshore developed 164.1 92.9 56.6 Dashtak Formation is shown to Total 31,423.8 23,825.2 contain gas and condensates. Note: NR = not reported, NC = not calculated.

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Table 4 Table 5 Asmari Reservoir in Giant Fields Iran’s Cumulative Production (CP), Initial-Oil-In-Place (IOIP), Estimated Total Remaining Reserves (TRR) and Ultimate Recoverable Reserves (EURR) Estimated Ultimate Recoverable and Recovery Factor (RF) (million barrel). Reserves (EURR) 1974-2004 (billion barrel). RF Year CP TRR EURR Reference Field IOIP EURR in % Gachsaran 49,342 31* 1974 20.2 66.0 86.2 OPEC 1994 Marun 46,665 21,962 47 1975 22.1 64.5 86.6 OPEC 1994 Agha Jari 27,942 58* 1976 24.3 63.0 87.3 OPEC 1994 Ahwaz 27,913 17,923 64 1977 26.3 62.0 88.3 OPEC 1994 Bibi Hakimeh 14,890 33* 1978 28.3 60.1 88.4 OPEC 1994 Parsi 12,651 3,811 30 1979 29.4 58.8 88.2 OPEC 1994 Rag-e-Safid 12,069 27* 1980 29.7 58.3 88.0 OPEC 1994 Karanj 8,822 51* 1981 30.2 57.0 87.2 OPEC 1994 Haft Kel 8,575 1,946 23 1982 31.1 56.2 87.3 OPEC 1994 Pazanan 7,555 1,854 25 1983 31.9 55.3 87.2 OPEC 1994 Masjid-e-Sulayman 6,628 1,329 20 1983 48.0 Hemer and Pickford Kupal 5,918 21* 1984 32.7 58.8 91.5 OPEC 1994 Ramin 5,700 1985 33.5 59.0 92.5 OPEC 1994 Mansouri 3,731 1,747 47 1986 34.2 92.9 127.1 OPEC 1994 Kilur 3,385 264 8 1987 35.1 92.9 128.0 OPEC 1994 Shadegan 3,099 1987 36.0 49.0 85.0 Beydoun 1988 Ghalehnar 2,597 465 18 1988 36.0 92.9 128.9 OPEC 1994 Neft-e-Safid 2,388 21* 1989 37.0 92.9 129.9 OPEC 1994 Chesmeh Khosh 2,255 840 37 1990 38.1 92.9 131.0 OPEC 1994 Ramshir 1,763 592 34 1991 39.4 92.9 132.3 OPEC 1994 Lab-e-Safid 1,556 508 33 1992 40.6 92.9 133.5 OPEC 1994 Karoon 1,171 1993 41.9 92.9 134.8 OPEC 1994 Danan 1,061 1994 43.2 94.3 137.5 OPEC 1994 Abuzar 893 135 15 1995 44.5 92.0 136.5 APRC 1996 Total 258,211 1996 45.8 88.0 133.8 APRC 1997 1996 59.0 Alsharhan and Nairn Note: * Asmari and Bangestan reservoirs. 1997 47.1 93.0 140.1 APRC 1999 1997 78.6 Petroconsultants DATA BASE FOR IRAN’S RESERVES 1998 48.5 1999 49.8 96.4 146.2 APRC 2003 Table 5 lists Iran’s cumulative production 2000 51.1 (CP), remaining total proved reserves (TRR) 2001 52.4 97.3 149.7 MEES 2003 and estimated ultimate recoverable reserves 2002 53.6 130.8 184.4 MEES 2003 (EURR) since 1974. The remaining and ultimate 2003 55.0 133.3 188.3 BP 2005 recoverable include condensates, which account 2004 56.9 132.5 189.4 BP 2005 for about 24 Gb (Table 3). To illustrate some of the 2005 57.9 2006 59.3 confusion in the literature in regards to reporting reserves, four examples are illustrated here and shown in Table 5.

1. Hemer and Pickford (1984) reported that according to Iran’s National Energy Committee, the estimated crude oil reserves (which could be produced through primary recovery methods) were 48.0 Gb in 1983; but this quantity is 7.3 Gb less than the 55.3 Gb reported for 1983 by Iran (in OPEC, 1994). 2. Beydoun (1988) reported that Iran’s crude oil reserves were 49.0 Gb in 1987; but this quantity is substantially less than the 92.9 Gb reported for 1986 by Iran (in OPEC, 1994). 3. Alsharhan and Nairn (1997) reported Iran’s ultimate recoverable crude oil reserves (EURR) are 59.0 Gb; but this is less than half of the EURR for 1996 (133.8 Gb), and more likely to reflect the total remaining reserves in the mid-1980s. 4. In 1997, according to APRC (1999), Petroconsultants (now IHSE) reported total remaining reserves as 78.6 Gb compared to Iran’s reported 93.0 Gb.

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Table 5 shows that Iran’s official EURR (cumulative production + estimated proved total remaining reserves) of crude oil and condensate have more than doubled from about 86.2 Gb to 189.4 Gb in the past 30 years. A major source of this reserves growth is due to improved (IOR) and enhanced recovery (EOR) in mature fields, and to a lesser extent exploration. For example, in 2003, Iran’s Ministry of Petroleum reported that the total reserves of oil and condensate at end-2002 stood at 130.8 Gb, and represented a growth of about 35% over the end-1999 reserves. For this 3-year period (2000–2002), Iran reported net reserves growth of 33.5 Gb and 5.1 Gb from newly discovered fields, and production as 4.3 Gb (average of 3.9 Mb/d). The reserves growth are largely due to IOR and EOR projects and approximately reflected by the secondary remaining reserves in Table 2. In some oil field practices reserves growth due to IOR and EOR are not considered as proved until a pilot project confirms the additional commercial recoveries.

In support of the 2002 reassessment of its reserves, Iran’s Ministry of Petroleum submitted a document to OPEC that estimated the remaining recoverable oil and condensate reserves in all of its oil and gas fields as of the end of 1999 (reproduced in MEES, 24 November, 2003). In the submission, the post- 1999 reserves were reported for those fields that provided the additions (reproduced in MEES, 1 December, 2003; APRC, 2005). The oil and condensate fields are listed in Tables 2 and 3 in alphabetical order (column 1). The reservoirs (column 2) are listed in increasing stratigraphic age (Figures 3 and 4). Some reservoirs are sometimes reported individually (e.g. Asmari), while others correspond to several reservoirs (e.g. Bangestan reservoir consisting of the Ilam and Sarvak reservoirs; or Khami consisting of several Jurassic-Lower Cretaceous reservoirs such as the Fahliyan reservoir, Figures 3 and 4).

By combining the information from the Iranian Government’s report (MEES, 24 November and 1 December 2003; APRC 2005), Table 2 shows for crude oil:

• Column 3: Initial-oil-in-place (IOIP) at the end of 1999; • Column 4: Initial-oil-in-place (IOIP) at the end of 2002; • Column 5: Estimated ultimate recoverable reserves (EURR) at the end of 1999; • Column 6: Estimated ultimate recoverable reserves (EURR) at the end of 2002; • Column 7: Primary remaining reserves (PRR) at the end of 1999; • Column 8: Secondary remaining reserves (SRR) at the end of 1999 (SRR-99); • Column 9: Total remaining reserves (TRR) at the end of 1999.

Table 3 provides similar data for condensates. In MEES (24 November 2003) no reserves are reported by individual field for:

(1) Onshore developed fields that had less than 50 Mb (shown as 5 Mb in MEES) of crude oil (TRR = 522.3 Mb); (2) Onshore undeveloped fields that had less than 50 Mb of crude oil (TRR = 525.8 Mb); (3) Offshore developed fields that had less than 50 Mb of crude oil (TRR = 320.8 Mb); (4) Offshore undeveloped fields that had less than 50 Mb of crude oil (TRR = 129.7 Mb); (5) Onshore developed gas fields with less than 50 Mb of condensate (TRR = 92.9 Mb).

Tables 2 and 3 also show, where the reported information permits computation:

• Column 10: Cumulative production (CP) at the end of 1999 (subtracting the TRR from the EURR); • Column 11: Recovery factor (RF) computed at the end-2002 (100xEURR/IOIP); • Column 12: Percentage of EURR produced at the end of 1999 (100xCP/EURR of 2002); • Column 13: Percentage of IOIP produced at the end of 1999 (100xCP/IOIP of 2002).

PRODUCTION HISTORY OF IRAN

Production During 1908–1952 and the Valleys of 1941 and 1952

The year 2008 will mark the Centenary since the first discovery of oil in the Asmari Formation in the Masjid-e-Sulayman field in Iran (Figure 2). This field was not only the first discovery of oil in the Middle East, but also turned the attention of worldwide exploration from sandstone to carbonate

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reservoirs (Schlumberger, 2003). Masjid-e-Sulayman started producing oil in 1913 at a rate of 5 Kb/d. By 1927 its production had reached 100 Kb/d, and probably continued to account for most of Iran’s production until about 1930. It was still in production in 2005 at the rate 4.5 Kb/d, and by end- 2006 will have produced a total of 1.11 Gb from an estimated initial-oil-in-place of 6.63 Gb. With an enhanced oil recovery (EOR) development project underway, production is scheduled to rise to 20 Kb/d in the near future.

Another five fields were discovered in the years from 1928 to 1939, when World War IIstarted, comprising Neft-e-Shar in 1927, Gachsaran and Haft Kel in 1928, Agha Jari in 1936 and Lali in 1938. Production continued to climb steadily until just before World War II when it reached about 214 Kb/d (Figure 1), but then declined during the war to a low of about 139 Kb/d in 1941. It recovered after the war to 664 Kb/d in 1950, but then declined between 1951 and 1955 as a result of the 1952 Revolution and embargo, falling to a low of 27 Kb/d in 1952. No new giant fields were discovered in the period 1946 to 1952. In summary, Iran’s production between 1913 and 1952 can be characterized by two peaks (1938 and 1950) and two valleys (1941 and 1952).

Production During 1952–1981 and the 1974 Peak

Crude oil production increased systematically from the low of 27 Kb/d in 1952 to the peak of 6.02 Mb/d in 1974 (Figure 1). Production increased 6-fold from 1959 to 1974, rising by about 1.0 Mb/d every 2–3 years, and remained at a high rate until the revolution of December 1979 and the nationalization of the industry, when it fell to 3.17 Mb/d (Figure 1). The start of the Iran-Iraq War in September 1980, less than a year after the 1979 Revolution, had a further impact with production dropping to 1.57 Mb/ d (Figure 1). The war damaged refineries, terminals, petrochemical complexes and, in particular, the main shipping facility at Kharj Island (Figure 2). Exports came to a near standstill by September 1980 and by the end of the year had recovered to no more than 350 Kb/d, compared to nearly 4.0 Mb/d in 1974. But production rose in 1981 to 1.33 Mb/d with exports ranging between 600 Kb/d to 1.3 Mb/d.

The history of production from 1974 to 1978 shows that the decline commenced after 1974 and was not entirely due to the events of 1979 and 1980 (Figure 1 and Table 6). In 1975 it fell by 672 Kb/d to 5.35 Mb/d. It reached a second peak of 5.88 Mb/d in 1976, before declining to 5.24 Mb/d in 1978. This decline occurred despite a sharp rise in oil price from $2.50 to $10.0 per barrel in 1974 and $40 per barrel in 1979, and despite the Government’s desire to increase production.

Iran’s production between 1959 and 1978 is reported by field in the literature. It shows that production from the Bangestan reservoir in the Lali field (Figure 2, IOIP = 737 Mb), which went on stream in 1948 and was producing 15 Kb/d in 1959, had ceased production by 1973. Production from another three giant fields systematically declined between 1959 and 1978 (Table 6): Haft Kel (150 to 4 Kb/d; IOIP = 8.6 Gb), Masjid-e-Sulayman (45 to 8 Kb/d; IOIP = 6.6 Gb) and Neft-e-Safid (54 to 30 Kb/d; IOIP = 3.0 Gb) (Figure 2).

Another ten giant fields attained peak production between 1971 and 1976 followed by declines (Figure 2 and Table 6). In alphabetical order these are:

1. Agha Jari (IOIP = 30.2 Gb) production attained a peak of just over 1.0 Mb/d in 1973 when it represented 20% of Iran’s annual production. By 1978 production had declined by 46% to 638 Kb/d. 2. Bibi Hakimeh (IOIP = 17 Gb) production attained a peak of 446 Kb/d in 1971 when it represented 10% of Iran’s annual production. The production maximum occurred 8 years after it went on stream and then declined by 45% to 245 Kb/d in 1978. 3. Binak (IOIP = 3.3 Gb) production attained a peak of 55 Kb/d in 1974, 8 years after it went on stream. Production then declined to between 32–45 Kb/d in 1975–1977 but went back up to 54 Kb/d in 1978. 4. Doroud (also Kharj; IOIP = 14 Gb) production attained a peak of 73 Kb/d in 1973 – 10 years after it went on stream, and then declined by 38% to 48 Kb/d in 1978. 5. Gachsaran (IOIP = 53.4 Gb) production attained a peak of about 922 Kb/d in 1974 when it represented 18% of Iran’s annual production. By 1978 production had declined by 17% to 767 Kb/d.

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6. Karanj (IOIP = 10.4 Gb) production attained a peak of 297 Kb/d in 1974 – 11 years after it went on stream, and then declined by 12% to 260 Kb/d in 1978. 7. Marun (IOIP = 49.7 Gb) production attained a peak of 1.341 Mb/d in 1976, 12 years after it went on stream. In 1976 it accounted for 23% of Iran’s annual production. By 1978 production had declined by 5% to 1.278 Mb/d in 1978. 8. Parsi (also Faris or Paris; IOIP = 12.3 Gb) production attained a peak of 451 Kb/d in 1973 – 8 years after it went on stream, and then declined by 40% to 267 Kb/d in 1978. 9. Pazanan (IOIP = 7.6 Gb) production attained an early maximum in 1966 at 76 Kb/d just four years after start-up, then declined throughout 1968–1976 before returning to 81 Kb/d in 1978. 10. Rag-e-Safid (IOIP = 18.7 Gb) attained a peak of 289 Kb/d in 1974 – 9 years after it went on stream, and then declined by 43% to 164 Kb/d in 1978.

Of the ten fields for which the start-up year is known (Table 6), peak production occurred between eight and sixteen years after the field went into production. The production declines ranged between 38–46% in five of the fields between peak year and 1978. The decline in the Binak Field from 1974 to 1975 was anomalously steep (from 55 to 32 Kb/d) but it recovered to a near-maximum rate of 54 Kb/d in 1978. For the two supergiants, Marun and Gachsaran, the combined production drop was 224 Kb/d representing relatively shallow declines of 5% and 17%, respectively.

Only the supergiant Ahwaz field shows a systematic increase in production, climbing from about 6 Kb/d in 1960 to more than 1.1 Mb/d in 1978 when it represented 20% of the country’s total production (Table 6). The fields in Table 6 are grouped to show their relative contributions in terms ofthree production ranges: (1–6) 45–160 Kb/d; (7-10) 160–450 Kb/d; (11–14) the four supergiants (Agha Jari, Ahwaz, Gachsaran and Marun). The 14 fields together, consistently produced more than 88% of the country’s total production in the 1960s and 1970s, with the four supergiants accounting for 64–85%. The next rank of fields (Bibi Hakimeh, Karanj, Parsi, Rag-e-Safid) accounted for another 17–23% of total production during the 1970s.

In summary, about 90% of the country’s production during the 1953–1978 period came from only fourteen fields (Table 6). The peak of 6.0 Mb/d in 1974 was achieved largely by the start-upof three supergiant fields in the 1960s (Ahwaz, Gachsaran and Marun), which together with Agha Jari accounted for about two-thirds of the total production in the 1970s. Production from all but three of the fourteen fields (Ahwaz, Binak and Pazanan), however, had decreased by 1978, prior to the 1979 Revolution and 1980–88 Iran-Iraq War. It seems evident that the decline was mainly imposed by natural decline and the physics of the reservoirs.

1982 to 2006: The Steady Production Build-up

Since 1982, Iran has built-up its crude production capacity steadily, passing 3.0 Mb/d in 1990. As of the start of 2006, MEES (13 February 2006) estimated Iran’s installed crude production capacity was just less than 4.2 Mb/d (Table 1). In 2005 Iran’s daily production was about 4.1 Mb/d, with exports of about 2.5 Mb/d. The four supergiant fields provided about half of total production (Table 6).

Table 6 shows the 2005 production capacity of the main fields developed in the 1970s, as well as current capacity as a percentage of peak rate. Only the offshore Doroud field shows an increase from 48 Kb/d in 1978 to 130 Kb/d in 2005, and a further expansion to 220 Kb/d is planned (Table 1). Fields that are producing at rates that are comparable to their peak 1970s levels are Binak (91%), Pazanan (86%) and to a lesser extent Ahwaz (77%) and Rag-e-Safid (66%).

Gachsaran field is apparently producing at about 61% of its peak level, but as discussed below may infact be producing less. Apart from the six fields noted above, the remaining fields that were contributing significantly to 1970s production are producing at between 20–50% of their peak levels. Of the fields noted in Table 6, six are planned for increased production (Table 1; Ahwaz-Bangestan, Doroud, Masjid-e-Sulayman, Parsi, Pazanan and Rag-e-Safid).

Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/12/2/69/4570022/husseini.pdf by guest on 24 September 2021 Iran’s oil reserves and production 1 8 6 9 2 28 9 28 46 91 25 61 5 6 2 86 77 54 6 2 44 39 19 2 05/ 1 Max 5 0 9 0 0 0 0 0 0 0 0 0 5 8 4 52 74 50 40 25 70 14 31 56 52 13 15 57 13 19 19 10 85 2005 2,12 4,10 2 8 9 0 8 4 6 25 67 4 45 67 54 81 94 48 72 30 18 ,242 26 63 16 93 1978 3,79 1,27 1,10 3 5 4 7 1 2 0 2 4 2 4 4 59 34 47 7 8 98 27 88 68 30 45 79 12 17 ,857 ,292 ,082 82 26 20 25 1977 5,66 1 1 3 3 9 9 4 1 2 1 0 2 5 6 23 86 61 70 88 39 37 65 21 11 28 19 34 ,883 26 22 83 1976 1,34 3,85 1,12 1,05 7 1 0 5 5 1 2 6 4 1 6 6 5 3 0 9 1 3 3 90 70 30 17 29 36 32 11 26 23 21 68 90 19 83 41 17 1975 3,72 1,19 5,35 1,02 2 97 57 91 22 59 33 89 65 91 35 22 36 34 16 55 ,054 ,926 ,022 ,305 57 36 1974 1 6 2 3 3 9 9 1 6 1 7 9 8 2 6 3 1 2 0 2 3 9 1 4 4 65 38 24 22 91 32 18 55 88 19 36 27 73 24 85 45 1973 5,86 3,82 1,02 1,05 1,28 5 7 4 2 1 8 15 36 86 98 57 64 90 21 32 41 18 52 ,023 37 63 86 94 1972 3,22 1,07 1,04 0 5 6 4 8 3 6 1 5 2 2 4 4 82 68 93 8 9 66 64 91 32 23 44 27 36 22 ,909 ,026 44 34 19 18 1971 4,54 0 2 4 1 2 8 9 8 9 8 0 2 3 4 5 86 35 20 30 68 69 91 17 43 32 38 17 ,829 64 84 73 81 26 10 1970 2,66 6 3 2 4 1 7 9 4 3 0 9 1 6 4 6 71 20 22 31 49 41 92 18 14 73 23 72 86 58 36 48 24 19 1969 3,37 2,41 ble 2 3 25 46 29 Ta 95 30 65 15 83 18 15 73 561 427 304 434 879 203 193 1968 2,840 2,070 0 1 8 7 6 5 77 35 21 95 22 82 73 19 13 75 350 665 919 218 228 158 164 1967 2,603 1,906 2 5 8 9 7 94 31 27 76 11 77 95 70 781 236 645 171 151 2,132 1966 1,642 9 7 0 4 0 4 0 5 23 94 34 24 10 38 79 186 509 833 104 107 166 1965 1,908 1,508 1 9 0 1 5 6 8 0 6 38 23 97 85 19 12 11 865 199 449 135 1,71 1964 1,449 0 3 0 39 28 97 83 97 16 14 129 212 785 358 1963 1,491 1,240 0 0 0 0 0 39 31 33 82 97 15 287 203 771 133 1962 1,091 1,335 Production for main 14 fields: 1959-1978 and 2005 (1,000 barrels oil per day). 35 33 80 96 16 707 967 125 193 253 1961 1,202 0 00 0 0 6 7 47 41 23 74 97 250 670 11 786 162 1,068 1960 0 0 0 45 54 27 59 71 98 928 150 249 599 658 1959 6 6 to 14 to 14 ar 11 11 Ye l ta To M-e-Sulayman Haft Kel Neft-e-Safid Doroud Binak Pazanan Subtotal 1 to Percent 1 to Karanj Rag-e-Safid Bibi Hakimeh Parsi Subtotal 7 to 10 Percent 7 to 10 Gachsaran Agha Jari Marun Ahwaz Subtotal Percent Percent 1 to 14 1 2 3 4 5 6 7 8 9 11 10 12 13 14

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THE FOUR SUPERGIANTS OF IRAN

Production profiles of the four supergiant fields are evaluated below on the basis of physical parameters, based on published sources, including reports by the Ministry of Petroleum (in APRC, 2005 and MEES, 24 November and 1 December 2003), which have been compared with previous published estimates (e.g. Burke and Gardner 1969, in Kamen-Kaye, 1970; AAPG, 1960–1979; Beydoun, 1988; IEA, 1995; Petroleum Economist, 1996; Christian, 1997; IHSE in Mann et al., 2003). The approximate production profile and end-2006 status for each field is estimated by using several independent sets of data, including production rates when available (e.g. for 1959–1978 from AAPG; for 1994-2005 from OPEC in APRC; for 2005 from MEES, 13 February 2006) giving a good review of production over an extended period of time. A second data set is cumulative production (e.g. for mid-1978 from Beydoun; for 1997 from NIOC), which gives average production rate for the period 1978–1997. The third independent data set is the cumulative production for end-1999 as calculated from Iran’s reported estimated ultimate recoverable reserves (EURR) and total remaining reserves for 1999.

Agha Jari (Aghajari) Field

Reservoir According to Beydoun (1988) the Asmari and Sarvak reservoirs in Agha Jari field were discovered in 1936 and 1956, respectively (Figures 2–4). The trap is an elongated NW-trending anticline that is about 56 x 6 km in area (NIOC, 1998) and has a strong surface expression that is 22 x 5 km in area (Beydoun, 1988). The primary Asmari reservoir is at a depth of about 760 m (2,500 ft) (Alsharhan and Nairn, 1997). The formation is more than 457 m (1,500 ft) thick and the average porosity is 7.6%. (Alsharhan and Nairn, 1997). The secondary Sarvak reservoir is at a depth of about 2,000 m (6,560 ft) and has a thickness of 915 m (3,000 ft) (Beydoun, 1988) and a porosity of 5.0–9.5% (NIOC, 1998).

Although they are separated by 670 m (2,197 ft) of tight strata, Alsharhan and Nairn (1997) reported that the Asmari and Sarvak reservoirs appear to be in communication. As an example for the evidence for communication, they cite the equal pressure drops measured in two wells that are 12 km apart. The communication is also supported by the common specific gravity of the Asmari and Sarvak oils o (34.6 API) and similar H2S content of 1.42% and 1.38% (Beydoun, 1988; Alsharhan and Nairn, 1997).

Production The Asmari reservoir in Agha Jari field went on stream in 1945 with individual wells producing as much as 40 Kb/d (Beydoun, 1988). In 1956, production started from the Sarvak reservoir. By 1959 production was about 600 Kb/d and accounted for nearly 65% of Iran’s total production (Table 6). Production climbed rapidly after 1960 reaching a peak of 1.023 Mb/d in 1973 after which it decreased to about 640 Kb/d in 1978 (Tables 6 and 7). NIOC (1998) reported that due to the thinning oil column, production was decreased to 120 Kb/d (unspecified year but probably in 1979; Table 7) resulting in the oil column increasing from 400 to 700 ft.

Some reported production rates are as follows:

• 340 Kb/d for 1993 (APRC, 1994); • 250 Kb/d for 1994–1995 (APRC, 1995, 1996; IEA, 1995); • 190 Kb/d for 1997–2004 (APRC, 1999–2005; NIOC, 1998); • 200 Kb/d at the start of 2006 (MEES, 13 February 2006). • M. Lynch (2006) quoted recent reports that estimate production at 180 Kb/d in February 2006 from 165 wells, and down from 195 Kb/d in 2001.

At the end of 1997, NIOC (1998) reported that a total of 161 wells were drilled in the field: 137 in the Asmari, 7 in the Sarvak and one in the deeper Khami reservoir. Only four of the eight deeper wells produced oil. At the end of 1997, 73 wells were on stream and each produced about 2 Kb/d (total 189.8 Kb/d as consistent with cited production rate of 190 Kb/d for 1997). The average productivity index is 600 barrels/day/psi and the gas/oil ratio is 650 cubic feet/barrel. In 1997, the main drive mechanism was the gas-cap expansion, which provided 70% of the pressure support , with the balance coming from natural water drive (> 20%) and rock and fluid expansion.

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Beydoun (1988) reported that by mid-1978 Table 7 the field had produced 6.86 Gb. NIOC (1998) Agha Jari Field Production History (1959–2006). reported that cumulative production as of Daily Annual Cumulative Reference Year end-1997 was 8.4 Gb from the Asmari and (Kb/d) (Mb) (Gb) 340 Mb from the Sarvak, for a total of 8.74 Hotchkiss 1960 1959 599 219 1.13 Gb. Thus, a total of 1.88 Gb was produced Hotchkiss 1961 1960 670 245 1.38 for the period from mid-1978 to 1997 (total Hotchkiss 1962 1961 707 258 1.64 19.5 years) giving an average 265 Kb/d Hotchkiss 1963 1962 771 281 1.92 for the interval. In Table 7 the production Hotchkiss 1964 1963 785 287 2.20 history is constructed from the cumulative Hotchkiss 1965 1964 866 316 2.52 production reported for end-1997 (NIOC, Mason & Moore 1966 1965 833 304 2.82 1998) and mid-1978 (Beydoun, 1988), Mason & Moore 1967 1966 781 285 3.11 respecting the maximum of 250 Kb/d as Mason & Moore 1968 1967 919 335 3.44 reported for 1994 (APRC, 1995; IEA, 1995). Mason & Moore 1969 1968 879 321 3.76 Mason & Moore 1970 1969 861 314 4.08 Initial-Oil-in-Place (IOIP) Mason & Moore 1971 1970 819 299 4.38 Mason et al. 1972 1971 868 317 4.69 The IOIP in Agha Jari field is reported Mason et al. 1973 1972 948 346 5.04 variously as 31 Gb (IEA, 1995) or 28 Gb Mason et al. 1974 1973 1,023 373 5.41 (Petroleum Economist, 1996). In 2002, Iran Hasson et al. 1975 1974 991 362 5.78 (in MEES, 24 November 2003; APRC, 2005) Hasson et al. 1976 1975 830 303 6.08 estimated IOIP as 30.2 Gb (Table 8). Hasson et al. 1977 1976 835 305 6.38 Hasson et al. 1978 1977 659 241 6.62 Estimated Ultimate Recoverable Hasson et al. 1979 1978 638 233 6.86 Reserves (EURR) estimated rate 1979-1996 265 97 The ultimate recovery from Agha Jari field estimated rate 1997 190 69 8.74 is variously reported at 9.5 Gb (Burke estimated rate 1998 190 69 and Gardner, 1969, in Kamen-Kaye, 1970; estimated rate 1999 190 69 8.88 estimated rate 2000-2006 190 69 9.40 Christian, 1997), or 8.7 Gb (Beydoun, 1988), or 5.76 Gb (Mann et al. 2003, based Cumulative production (CP) in 1978 after Beydoun (1988). Average production after 1987 estimated from CP in 1997 (NIOC, 1998) and on IHSE data base). CP in 1999 from EURR - TRR .

The National Iranian Oil Company is Table 8 planning a secondary recovery program Summary of Agha Jari Field (billion barrels). for Agha Jari field that involves injecting gas at a rate of 1.8 BCF/day from the Reservoir Asmari Sarvak Total North and South Pars fields (NIOC, 1998; Gravity API 34.6° 34.6° APRC, 2004). Simulation studies by NIOC Hydrogen Sulfide 1.38% 1.42% estimate that the injection of 20 TCF could IOIP 1999 27.9 2.3 30.2 result in the recovery of an additional IOIP 2002 27.9 2.3 30.2 5.0 Gb of crude oil. According to official EURR 1999 NR NR 15.6 reports in 2002, the estimated recovery PRR 1999 1.5 0.12 1.6 from the undifferentiated Asmari and SRR 1999 NR NR 5.1 Bangestan reservoirs has increased from TRR 1999 NR NR 6.7 15.6 to 17.4 Gb (MEES, 1 December 2003; EURR 2002 NR NR 17.4 NC NC 8.8 APRC, 2005). CP end-1999 CP end-2006 NC NC 9.4 TRR-2006 NC NC 8.0 Cumulative Production (CP) CP/IOIP end-2006 NC NC 31.1% According to NIOC (1998) cumulative CP/EURR end-2006 NC NC 54.0% production through 1997 was 8.74 Gb. Recovery Factor NC NC 57.6% Assuming that production from end-1997 See Table 2 on page 74 for abbreviations. to end-1999 (2 years) averaged 190 Kb/d, that would add 139 Mb, giving cumulative production through 1999 at 8.88 Gb. This estimate is confirmed by subtracting reported reserves of 6.7 Gb from ultimate recovery of 15.6 Gb, which amounts to 8.9 Gb. Additionally, APRC (2005) reported that some 8.9 Gb has been produced without specifying the reference year. Assuming the production for 2000–2006 (7 years) also averaged 190 Kb/d (Table 7), then about another 485 Mb of production would bring cumulative production in 2006 to about 9.4 Gb. It means that 54% of the

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ultimate recovery has been produced, and Table 9 about one-third of the oil-in-place has been Ahwaz Field Production History (1959–2006). extracted. Reference for Daily Annual Cumulative Year Production (Kb/d) (Mb) (Gb) Summary Hotchkiss 1960 1959 0 0 0.00 The Agha Jari field has about 30.2 Gb of Hotchkiss 1961 1960 6 2 0.002 initial-oil-in-place, of which more than Hotchkiss 1962 1961 7 3 0.005 90% is in the Asmari reservoir, and it is Hotchkiss 1963 1962 33 12 0.02 about 54% depleted. Production peaked Hotchkiss 1964 1963 97 35 0.05 in 1973 at about 1.0 Mb/d and the field Hotchkiss 1965 1964 135 49 0.10 has been producing at about 20–25% of Mason & Moore 1966 1965 166 61 0.16 the peak rate for the past thirty years. Mason & Moore 1967 1966 171 62 0.22 Mason & Moore 1968 1967 164 62 0.28 Annual production since the 1980s relative Mason & Moore 1969 1968 203 74 0.36 to the IOIP and EURR is 0.25% and 0.40%, Mason & Moore 1970 1969 240 88 0.45 respectively. The recovery factor at 57.6% Mason & Moore 1971 1970 266 97 0.54 is relatively high compared to other fields. Mason et al. 1972 1971 262 96 0.64 The primary reserve-to-production ratio Mason et al. 1973 1972 372 136 0.77 is approximately 14 years, but production Mason et al. 1974 1973 853 311 1.08 will last much longer at a declining rate. Hasson et al. 1975 1974 959 350 1.43 Hasson et al. 1976 1975 1,025 374 1.81 Ahwaz Field Hasson et al. 1977 1976 1,054 385 2.19 Hasson et al. 1978 1977 1,082 395 2.59 Reservoir Hasson et al. 1979 1978 1,109 405 2.99 The Ahwaz field, which was discovered estimated rate 1979-1998 1,000 365 in 1958 (Beydoun, 1988), lies on an estimated rate 1999 1,000 365 10.62 estimated rate 2000-2006 855 312 12.81 elongated NW-trending anticline about 80 x 10.5 km in extent (Schlumberger, 2003). Average production for 1979–1999 based on cumulative production in 1999 (EURR - TRR) and in 1978. The Asmari reservoir lies at a depth of 2,485 m (8,150 ft) (Petroleum Economist, 1996; APRC, 2005) and contains 32.6o API

oil with 1.5% H2S (Beydoun, 1988). As noted earlier, it consists of eight sandstone and six carbonate layers (Schlumberger, 2003). The Asmari sandstone layers have high porosity and permeability and provide most of the production.

The Bangestan reservoir (Sarvak + Ilam reservoirs) has an average porosity of 11%. It’s depth is uncertain being variously reported at about 10,000 ft (NIOC, 1998) or 12,000 ft (Petroleum Economist, 1996; APRC, 2005). The specific gravity and sulfur content are also variably reported in the literature. o Tables 1 and 10 show the quantities reported by Beydoun (1988): 26 API and 1.3% H2S for the Sarvak o o and 29 API and high H2S for the Ilam, and as reported by NIOC (1998) for the Bangestan: 25.5 API

and 3.5% H2S.

The Bangestan reservoir is divided into the upper Cretaceous (Coniacian-Campanian) Zones A to C in the Ilam Formation, and middle Cretaceous (Cenomanian-Turonian) Zones D to J in the Sarvak Formation. The most productive zones are Zone C (406–560 ft thick), Zone E (1,056 ft thick) and Zone I (490 ft thick). The field also contains oil in the Jurassic-Lower Cretaceous Khami Group.

Production The field went into production in 1959, and was producing 1.109 Mb/d in 1978 (Hemer etal., 1979). Based on the reported and estimated cumulative production for end-1978 and end-1999 it is estimated that the field produced on average about 1.0 Mb/d between 1979 and end-1999 (Table 9). This estimate is consistent with the IEA (1995) and APRC (1994–1999) reports for the late 1990s of 155–160 Kb/d from the Sarvak (Bangestan) and 800–830 Kb/d from the Asmari. MEES (13 February 2006) estimated the production capacity of Ahwaz field was 700 Kb/d from the Asmari and 155 Kb/d from the Bangestan by early 2006. M. Lynch (2006) quoted recent reports that estimated production from the Asmari and Bangestan as 725 and 125 Kb/d in early 2005, respectively.

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Table 10 Summary of Ahwaz Field (billion barrels). Reservoir Asmari Ilam Sarvak Bangestan Khami Total Gravity API 32.6° 29° 26° 25.5° NR Hydrogen Sulfide 1.5% high 1.3% 3.5% NR IOIP 1999 27.9 12.8 24.75 37.5 0.49 65.9 IOIP 2002 27.9 12.8 24.75 37.5 0.49 65.9 EURR 1999 14.3 NR NR 5.3 0.09 19.7 PRR 1999 6.2 1.5 2.2 3.7 0.08 9.9 SRR 1999 0.0 0.36 0.63 0.99 0.02 1.0 TRR 1999 6.2 1.88 2.8 4.68 0.09 10.9 EURR 2002 17.9 NR NR 7.7 0.09 25.7 CP end-1999 8.2 NC NC 2.45 0.00 10.6 CP end-2006 10.0 NC NC 2.85 0.00 12.8 TRR-2006 8.0 NC NC 4.84 0.09 12.9 CP/IOIP end-2006 35.6% NC NC 7.5% 0.00% 19.4% CP/EURR end-2006 45.5% NC NC 37.2% 0.00% 49.8% Recovery Factor 64.0% NC NC 20.5% 19.00% 39.0% Bangestan reservoir consists of Ilam and Sarvak reservoirs. See Table 2 on page 74 for abbreviations.

MEES (13 February 2006) also shows production from “Ahwaz-Mansouri” of 50 Kb/d (27.5o API) as well as production of 50 Kb/d (27.5o API) from “Mansouri field” with both entries noted for expansion by another 100 Kb/d. APRC (2005, p. 137) shows “Ahwaz-Mansouri” with a production capacity of 60 Kb/d (27.5o API) but does not include “Mansouri field” in their table. In Iran there is no “Mansouri reservoir” (e.g. Figures 3 and 4; Alsharhan and Nairn, 1997). It appears that reference to the “Ahwaz- Mansuri” is confused: it is a duplicate entry in MEES (13 February 2006) and incorrectly named as “Ahwaz-Mansouri” in APRC (2005). A separate field, known as Mansouri (also spelled Mansuri) field, was discovered in 1962 producing primarily from the Asmari reservoir.

In 1998, NIOC reported that 89 wells penetrated the Bangestan reservoir (Ilam and Sarvak formations) and of these 67 were on stream. The Ilam reservoir had about 10 wells, each producing about 1.0 Kb/d on average. The Sarvak wells each produce about 3.0 Kb/d. This would amount to about 181 Kb/d (3,000 x 57 + 1,000 x 10 = 181 Kb/d). But APRC (2005) reported that in 2004 the Bangestan reservoir was producing about 150 Kb/d from 60 wells and that production was expected to drop to 60 Kb/d if no additional enhanced recovery facilities were installed. Plans involve injecting 360 MCF of gas/day from Kabir Kuh field (APRC, 2004).

According to M. Naqavipur, Director of Planning and Integration at NIOC’s Karun Oil and Gas Company subsidiary (MEES, 5 June 2006), NIOC plans to increase the number of production wells in the field to 500 from the current 400. The infield drilling program will be undertaken in addition to a gas reinjection project in the Bangestan reservoir, which is intended to add 65 Kb/d of oil production to the current 155 Kb/d from this reservoir. This project involves drilling 36 production and injection wells, and conducting work-overs on 63 existing wells.

Oil-Initially-in-Place (IOIP) The IEA (1995) reported the initial-oil-in-place for the Bangestan reservoir as 47.2 Gb but this quantity must have included the Asmari reservoir because the Petroleum Economist (1996) reported IOIP as 47.25 Gb for both reservoirs. The official estimate at the end of 2002 was 65.9 Gb (MEES, 24 November 2003, see Table 10).

Estimated Ultimate Recoverable Reserves (EURR) Burke and Gardner (1969, in Kamen-Kaye, 1970) reported an ultimate recovery of 6.0 Gb, whereas Beydoun (1988) reported them as 10.1 Gb of which 75% are in the Asmari reservoir, and the ultimate recoverable gas is about 13 TCF. Mann et al. (2003 based on IHSE data base) reported 13.35 Gb, whereas the official estimate in 2002 revised the estimate up from 19.7 to 25.7 Gb (Table 10).

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Cumulative Production (CP) The field went on-stream in 1959 and had produced nearly 3.0 Gb by end-1978 according tothe annual quantities reported in Table 9. This estimate is consistent with the reported 2.78 Gb for mid- 1978 by Beydoun (1988). Cumulative production through 1999 is computed at 8.17 Gb and 2.45 Gb for the Asmari and Bangestan (Ilam and Sarvak) reservoirs, respectively, totaling 10.62 Gb. Assuming average production for 2000 to end-2006 (7 years) was 700 Kb/d for the Asmari and 155 Kb/d for the Bangestan, the cumulative production for end-2006 would 9.96 Gb and 2.85 Gb, respectively, and total 12.81 Gb (Table 10).

Summary The Ahwaz field relies mainly on the Asmari Reservoir, which has about 28 Gb of initial-oil-in-place. The sandstone layers account for the high recovery factor of 64%. The Asmari cumulative production as of end-2006 of about 10 Gb represents about 36% of oil-in-place and 46% of ultimate recovery. The primary reserve-to-production ratio is about 17 years. Over the past three decades annual production relative to the IOIP and EURR was about 1.15% and 1.8%.

Gachsaran (Gach Saran, Gach Qaraghuli) Field

Reservoir There is some confusion in the published literature about this field, which lies on a strongly asymmetrical anticline measuring 25 x 7 km (Beydoun, 1988) at a depth of 3,400 ft (1,036 m) (APRC (2005). The alternative reports concerning the Asmari Reservoir are compared below:

• Discovery: 1928 (Beydoun, 1988; APRC, 2005) or 1937 (Alsharhan and Nairn, 1997; Petroleum Economist, 1996). • Oil Column: 2,165 m (7,101 ft) (Beydoun, 1988); Thickness: 457 m (1,500 ft) (Alsharhan and Nairn, 1997). o o • Oil quality: 31.1 API and 1.7% H2S (Beydoun, 1988); 32 API and 1.6% H2S (Alsharhan and Nairn, 1997); 32o API (Petroleum Economist, 1996; APRC, 2005); 31o API (IEA, 1995; MEES 13 February, 2006).

Alsharhan and Nairn (1997) reported that the Asmari average porosity is 9% and that wells in the northwest zone produce higher rates (80 Kb/d) relative to wells in the southwest flank (40 Kb/d). Oil in the deeper Sarvak reservoir (Bangestan Group) and gas in the Khami Group were discovered in 1962 according to Beydoun (1988), or in 1956 according to Alsharhan and Nairn (1997). According to Beydoun (1988), the Asmari and Sarvak reservoirs are in pressure communication, and the Sarvak oil o has a gravity of 31.1 API and 1.7% H2S (Tables 1 and 12).

Production The production history of Gachsaran field since start-up in 1959 and up to 1978 is shown in Table 11. Beydoun (1988) reported that Gachsaran in 1978 produced on average 743 Kb/d, and had produced 4.45 Gb by mid-1978. Production in the late 1990s and early 2000s ranged between 585–600 Kb/d (IEA, 1995; APRC 1994-1995). In early 2006, production capacity stood at 560 Kb/d according to MEES (13 February 2006). M. Lynch (2006) quoted recent reports that estimate the late 2005 production as just 220 Kb/d, from 300 wells and down from 600 Kb/d in 2002.

Oil-Initially-in-Place (IOIP) The IEA (1995) and Petroleum Economist (1996) reported the IOIP in Gachsaran as 53 Gb. Iran (in MEES, 24 November 2003 and 1 December 2003; APRC, 2005) reported that the IOIP for the Asmari and Bangestan reservoirs is 49.4 and 3.6 Gb.

Estimated Ultimate Recoverable Reserves (EURR) The ultimate recovery has been estimated at 8.0 Gb (Burke and Gardner, 1969, in Kamen-Kaye, 1970), or 8.5 Gb (Beydoun, 1988), or 11.0 Gb (Christian, 1997). According to Beydoun (1988) the ultimate gas reserves are 21 TCF (including the Khami Group). Mann et al. (2003, based on IHSE data base) reported ultimate oil recovery is 11.8 Gb. Official Government reports (MEES, 1 December 2003;

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APRC (2005) indicated that the ultimate Table 11 recovery from the two reservoirs increased Gachsaran Field Production History (1959–2006). from 14.6 to 16.2 Gb due to EOR. Daily Annual Cumulative Reference Year (Kb/d) (Mb) (Gb) Cumulative Production (CP) Hotchkiss 1960 1959 59 22 0.02 Cumulative production through 1999 Hotchkiss 1961 1960 110 40 0.06 is calculated to be 8.2 Gb, to which Hotchkiss 1962 1961 252 92 0.15 subsequent production at an assumed 560 Hotchkiss 1963 1962 287 105 0.26 Kb/d would bring the total for end-2006 to Hotchkiss 1964 1963 358 131 0.39 9.6 Gb in 2006. Hotchkiss 1965 1964 449 164 0.55 Mason & Moore 1966 1965 509 186 0.74 Mason & Moore 1967 1966 645 235 0.97 Summary Mason & Moore 1968 1967 665 243 1.22 The Gachsaran Field has about 53 Gb of Mason & Moore 1969 1968 561 205 1.42 initial-oil-in-place of which 93% is in the Mason & Moore 1970 1969 724 264 1.69 Asmari reservoir. The recovery factor is Mason & Moore 1971 1970 842 307 1.99 31%. Cumulative production for end- Mason et al. 1972 1971 882 322 2.32 2006 is about 9.6 Gb and accounts for Mason et al. 1973 1972 861 314 2.63 17.9% of oil-in-place and 59.3% of the Mason et al. 1974 1973 887 324 2.95 ultimate recovery. The primary reserve-to- Hasson et al. 1975 1974 922 337 3.29 production ratio is 14 years. Over the past Hasson et al. 1976 1975 681 249 3.54 three decades annual production relative Hasson et al. 1977 1976 623 227 3.77 to oil-in-place and ultimate recovery was Hasson et al. 1978 1977 824 301 4.07 0.38% and 1.22%. Hasson et al. 1979 1978 767 280 4.35 estimated rate 1979-1998 475 173 Marun (Maroun) Field estimated rate 1999 475 173 8.16 estimated rate 2000-2006 560 204 9.60 Average production for 1979–1999 based on cumulative production Reservoir in 1999 (EURR - TRR) and in 1978 (Beydoun, 1988). The Marun field was discovered in 1964 (Beydoun, 1988) reaching the Asmari reservoir at a depth of 2,865 m (9,397 ft) Table 12 (Petroleum Economist, 1996; APRC, 2005). Summary of Gachsaran Field (billion barrels). The lithology of the reservoir is inter- Reservoir Asmari Sarvak Khami Total mediate between the sandy facies of Gravity API 31.1° 31.1° Ahwaz field and the carbonate facies of Hydrogen Sulfide 1.7% 1.7% other fields (Beydoun, 1988). The specific IOIP 1999 49.4 3.6 0.486 53.5 gravity of the Asmari oil is variously IOIP 2002 49.4 3.6 0.486 53.5 reported as follows: EURR 1999 NR NR 0.093 14.6 PRR 1999 NR NR 0.076 4.2 o • 33.0 API oil and a high-pressure gas SRR 1999 NR NR 0.017 2.2 dome (Beydoun, 1988); TRR 1999 NR NR 0.093 6.4 • 32.6o API (IEA, 1995); EURR 2002 NR NR 0.093 16.2 • 34.0o API (Petroleum Economist, 1996; CP end-1999 NC NC 0.0 8.2 APRC, 2005); CP end-2006 NC NC 0.0 9.6 • 32.0o API (MEES, 13 February 2006). TRR-2006 NC NC 0.1 6.8 CP/IOIP end-2006 NC NC 0.0% 17.9% The Sarvak reservoir contains oil with CP/EURR end-2006 NC NC 0.0% 59.3% a gravity of 32o API and a deeper Lower Recovery Factor NC NC 19.1% 30.7% Cretaceous reservoir contains gas See Table 2 on page 74 for abbreviations. (Beydoun, 1988).

Production The Marun Field went on-stream in 1965 and reached a maximum production level of 1.34 Mb/d in 1974 before declining to 1.28 Mb/d in 1978 (Tables 6 and 13). Reported production rates for the late 1990s and early 2000s range between 500–570 Kb/d (IEA, 1995; APRC 1994-1995). In early 2006 the field had a production capacity of 520 Kb/d according to MEES (13 February 2006) or 500 Kb/d according to M. Lynch (2006).

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Initial-Oil-in-Place (IOIP) Table 13 The IEA (1995) and Petroleum Economist Marun Field Production History (1965–2006). (1996) reported initial-oil-in-place of 52.1 Daily Annual Cumulative Reference Year Gb, whereas the official estimatesin ( (Kb/d) (Mb) (Bb) MEES, 1 December 2003; APRC, 2005) for Mason & Moore 1966 1965 0 0 0.00 the Asmari and Bangestan reservoirs are Mason & Moore 1967 1966 45 16 0.02 46.7 and 3.1 Gb, respectively, giving a total Mason & Moore 1968 1967 157 57 0.07 of 49.8 Gb. Mason & Moore 1969 1968 427 156 0.23 Mason & Moore 1970 1969 587 214 0.44 Estimated Ultimate Recoverable Mason & Moore 1971 1970 739 270 0.71 Mason et al. 1972 1971 893 326 1.04 Reserves (EURR) Mason et al. 1973 1972 1,044 381 1.42 The ultimate recovery has been variously Mason et al. 1974 1973 1,059 387 1.81 reported as 6.0 Gb (Burke and Gardner, Hasson et al. 1975 1974 1,054 385 2.19 1969, in Kamen-Kaye, 1970), or 12.0 Gb Hasson et al. 1976 1975 1,191 435 2.63 (Christian, 1997), or 12.6 Gb (Mann et Hasson et al. 1977 1976 1,341 489 3.12 al. (2003, based on IHSE data base). The Hasson et al. 1978 1977 1,292 472 3.59 official estimate for the Asmari reservoir Hasson et al. 1979 1978 1,278 466 4.05 has increased from 16.0 to 22.0 Gb (in estimated rate 1979-1998 520 190 MEES, 1 December 2003) (Table 14). The estimated rate 1999 520 190 8.00 ultimate recovery from the Bangestan estimated rate 2000-2006 520 190 9.30 reservoir has not been reported and the Production started in 1965. Average production for 1979–1999 total remaining reserves are comparatively based on cumulative production in 1999 (EURR - TRR) and in 1978. small at 231 Mb. Table 14 Cumulative Production (CP) Summary of Marun Field (billion barrels). Cumulative production may be calculated Reservoir Asmari Bangestan Total at 8.0 Gb by end 1999 from the above figures, Gravity API 33.0° 32.0° implying that production was running at Hydrogen Sulfide NR NR about 520 Kb/d from 1979 to 1999. This IOIP 1999 46.7 3.1 49.8 latter quantity is similar to the current IOIP 2002 46.7 3.1 49.8 production capacity of the field (Table EURR 1999 16.0 NR NC 13). If production has continued at this PRR 1999 5.3 0.18 5.5 rate since 1999, the end-2006 cumulative SRR 1999 2.7 0.05 2.8 production would be 9.3 Gb, amounting to TRR 1999 8.0 0.23 8.2 20% of oil-in-place (Table 14). EURR 2002 22.0 NR NC CP end-1999 8.0 NC NC Summary CP end-2006 9.3 NC NC Marun field has about 50 Gb of initial-oil- TRR-2006 12.6 NC NC in-place, of which 94% lies in the Asmari CP/IOIP end-2006 19.9% NC NC reservoir. The recovery factor of the CP/EURR end-2006 42.3% NC NC Asmari is 47%. Cumulative production Recovery Factor 47.1% NC NC as of end-2006 was about 9.3 Gb, or about See Table 2 on page 74 for abbreviations. 20% of the initial-oil-in-place and 42% of ultimate recovery. The primary reserve-to-production ratio is 21 years. Over the past three decades annual production relative to the initial-oil-in-place and ultimate recovery was 0.38% and 1.23%, respectively.

Reserves Growth in the Four Supergiant Fields

The apparent reserves growth in the four supergiant fields of Iran is very significant as listed in Table 15. The earliest 1969 estimates of ultimate recovery are from Burke and Gardner (1969, as quoted in Kamen-Kaye, 1970) and probably reflect estimates made by the operating international oil companies. The 1988 and 1997 estimates are from Beydoun (1988) and Christian (1997), and are probably from scouting reports by Petroconsultants (now IHSE). The source for 2003 are from Mann et al. (2003) published in AAPG’s Memoire 78 on giant fields. The official Iranian estimates are shown for 1999 and after the 2002 review. Table 15 shows that the 1969 estimates of ultimate recoverable reserves have been significantly exceeded by the cumulative production in the Ahwaz and Marun fields, and

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matched in Agha Jari and Gachsaran Table 15 fields. The official estimates of ultimate Four Supergiant Fields: Estimated Ultimate Recoverable recoverable reserves for all four fields, Reserves (EURR) in billion barrels for 1969–2002. reported in 2002, are nearly double Field Agha Jari Ahwaz Gachsaran Marun those of Burke and Gardner (1969). CP end-2006 9.40 12.80 9.60 9.30 Klett and Schmoker (2003) have Burke & Gardner 1969: EURR 9.50 6.00 9.60 6.00 reported on reserves growth for Beydoun 1988: EURR 8.70 10.10 8.50 9.50 the world’s giant fields (using Christian 1997: EURR 9.00 13.00 11.00 12.00 Petroconsultants/IHSE data bases) by Mann et al 2003 (IHSE): EURR 5.76 13.35 11.80 12.60 comparing reported reserves between Iran 1999: EURR 15.60 19.70 14.60 16.00 1981 and 1996. The quantities they Iran 2002: EURR 17.40 25.60 16.20 22.00 cited for reserves growth in the four Iran 2002: IOIP 30.20 65.60 52.90 49.70 fields are shown in Table 16. Also Recovery Factor % 57.6 39.0 30.7 44.3 shown are the estimates of reserves Mann et al. (2003, based on IHSE data base) reported: for Agha Jari (their growth for the longer period of 1969– field 317), EURR oil = 5.76 Gb, EURR gas = 9.9 TCF for total EURR = 1997 (13 years longer) by comparing 7.408 Gboe. For Ahwaz (their field 319), EURR oil = 13.35 Gb, gas = 23.3 the quantities reported by Burke and TCF for total EURR = 17.234 Gboe. For Gachsaran (their field 335), Gardner in 1969 and Christian in 1997. EURR oil = 11.8 Gb, EURR gas 31.1 TCF for total EURR = 16.984 Gboe. For Marun (their field 350), EURR oil = 12.63 Gb, EURR gas = 75.3 TCF The comparison shows that the total for total EURR = 25.18 Gboe.

Table 16 Reserves growth for Four Supergiant Fields (billion barrels).

Field Agha Jari Ahwaz Gachsaran Marun Total Klett & Schmoker (IHSE) 2003 1981 to 1996 5.30 4.84 6.50 4.90 21.50 Burke & Gardner 1967 and Christian 1997 1969 to 1997 -0.50 7.00 3.00 6.00 15.50 Burke & Gardner 1967 and Iran 2002 1969 to 2002 8.10 19.60 8.20 16.00 51.90 Klett and Schmoker (2003, based on Petroconsultants/IHSE data base) their table 1: Agha Jari = entry 13; Ahwaz = entry 10; Gachsaran = entry 9; and Marun = entry 12.

reserve growth for the four fields between 1981 and 1996 (21.5 Gb) is greater by about 25% than that of the longer interval of 1969–1997 (15.5 Gb). The discrepancy between the official estimates and other sources is 30.4–36.4 Gb.

FUTURE PRODUCTION CAPACITY

The crude oil production capacity of Iran, assuming the current and planned increases are completed by 2010 and 2015 without accounting for production decline (Table 1), is repeated in Table 17. The following four rows show the impact of subtracting 200, 300, 400 and 500 Kb/d per year, and the final three rows reduce production at a rate of 4%, 5% and 10% per year. Decline rates of 300–400 Kb/d and 500 Kb/d per year were reported by former Iranian Petroleum Minister B. Zanganeh (in MEES, 1 August 2005) and current Iranian Petroleum Minister Vaziri-Hameneh (in MEES, 18 September 2006), respectively.

The resulting production shows that Iran could achieve the country’s targeted 4.6 Mb/d capacity in 2009 if the net production decline rate is in the range of 5%/year or about 200 Kb/d/year. This decline rate would have to be achieved by a combination of infill drilling, recompletions, improved and enhanced recovery in developed fields, and from new production from undeveloped fields and reservoirs.

Considering Iran’s large reserves and the country’s peak production of 6.0 Mb/d in 1974, a 500 Kb/d net increment over three years would appear to be feasible (i.e. 4.1 to 4.6 Mb/d or 167 Kb/d/year in 2007–2009). However, using Hubbert’s Curve, C. Campbell (2006, written communication) predicted that Iran’s future production would be about 3.95 Mb/d between 2010–2030. He based this forecast on an estimate of the ultimate recoverable reserves for crude oil of 140 Gb, of which yet-to-find is 12.2 Gb and remaining reserves were 69.2 Gb for the end of 2005.

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It is not clear, however, whether this type of analysis is applicable to Iran’s Table 17 production because it does not resemble Decline Scenarios and Production Capacity Hubbert’s bell-shaped curve (see review of Iran: 2005–2015 (1,000 barrels oil per day). in Al-Husseini, 2006). Instead as seen in Decline Scenario end-2005 end-2009 end-2010 end-2015 Figure 1, it consists of numerous peaks and Zero Decline 4,148 5,555 5,555 5,955 valleys that were caused by events related to World War II (1939-1945), the early 200,000 b/d/year 4,148 4,755 4,555 3,955 300,000 b/d/year 4,148 4,355 4,055 2,955 1950s revolution and embargo, the 1979 400,000 b/d/year 4,148 3,955 3,555 1,955 Revolution, the Iran-Iraq War of 1980–88 500,000 b/d/year 4,148 3,555 3,055 955 and OPEC quota restrictions. It seems 4.0%/year 4,148 4,748 4,566 4,023 clear, however, that Iran’s oil production 5.0%/year 4,148 4,570 4,352 3,656 peaked in 1974 at 6.0 Mb/d when nearly 10.0%/year 4,148 3,794 3,449 2,296 all of the giant fields ramped-up to very high rates that were not sustainable a few years later (Table 6).

The 1974 peak production level of 6.0 Mb/d could therefore provide an important calibration for Iran’s ultimate recoverable reserves. This is because peak production rate (Mb/d) is approximately equal to .035 multiplied by the ultimate recoverable reserves (Gb). For EURRs of 140 and 168 Gb, the peak production rates are 4.90 and 5.88 Mb/d. The latter quantity is close to the two peaks attained in 1974 at 6.0 Mb/d and in 1978 at 5.88 Mb/d, and suggests that the ultimate recoverable reserves of Iran are in the range of 168 Gb. It is also interesting to note that production rates of 3.8 and 4.6 Mb/d correspond to one percent depletion rates for EURRs of 140 and 168 Gb.

A different approach to forecast Iran’s crude oil capacity was suggested by S.I. Al-Husseini (Oil and Money Conference, September 20-21, 2006, International Herald Tribune, London). He considered several key factors including reported ultimate recoverable and remaining reserves, production history, best-case scenario for enhanced recovery, and the investments required to overcome average decline rates in mature fields. Taking these factors together, he predicted that with sufficient financial investments Iran’s production would range between 3.8–3.9 Mb/d in the next decade but drop to 3.5 Mb/d by 2020.

CONCLUSIONS

This article reviewed numerous reports on Iran’s crude oil and condensate volumes (e.g. initial-oil-in- place, estimated ultimate recoverable reserves, etc.) including the most recent official reports (Tables 2 and 3). With reported remaining recoverable crude oil reserves of about 108 Gb in 2004, Iran holds about 10% of the world’s reserves. The main Asmari and Bangestan reservoirs contain about 43% and 25%, respectively, of the total crude oil-in-place of about 600 Gb. Expected recovery factors for the Oligocene-Miocene Asmari reservoir range between about 10–60%, and for the Cretaceous Bangestan reservoir between 20–30%, and reflect fractured reservoirs that are stratigraphically heterogeneous.

About half of Iran’s production comes from four mature supergiant fields that have depleted about half of their ultimate recoverable reserves (Tables 2, 6–14). They contain 25% of Iran’s initial-oil-in- place (Tables 2 and 4) and collectively peaked in 1974 when they were producing 3.9 Mb/d (versus about 2.1 Mb/d in 2005). The decline from 3.9 to to 2.1 Mb/d corresponds to a rate of about 2.0% per year on average.

Iran’s production peaked at 6.0 Mb/d in 1974, and in 2005 averaged about 4.1 Mb/d. The planned increase to 4.6 Mb/d by 2009 has to offset a total annual production decline rate of about 300–500 Kb/d from the maturing giant fields. To achieve this target, Iran has to add about 680 Kb/d/year in 2007–2009 from the developed and undeveloped fields and reservoirs (Tables 1 and 17).

ACKNOWLEDGEMENTS

The author would like to thank Hassan Al-Husseini, Colin Campbell and other colleagues for their useful comments.

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REFERENCES

Al-Husseini, M.I. 2006. The debate over Hubbert’s Peak, a review. GeoArabia, v. 11, no. 2, p. 181-210. Alsharhan, A.S. 2006. Sedimentological character and hydrocarbon parameters of the Middle Permian to Early Triassic Khuff Formation, United Arab Emirates. GeoArabia, v. 11, no. 3, p. 121-158. Ala, M.A., R.R.F. Kinghorn and M. Rahman 1980. Organic Geochemistry and Source Rock Characteristics of the Zagros Petroleum Province, Southwest Iran. Journal of Petroleum Geology, v. 3, no. 1, p. 61-89. Alsharhan, A.S. and A.E.M. Nairn 1997. Sedimentary Basins and Petroleum Geology of the Middle East. Elsevier, 843 p. Arab Petroleum Research Centre – APRC 1995. Arab Oil & Gas Directory 1994 to 2005. Arab Petroleum Research Centre, France Beydoun, Z.R. 1988. The Middle East: Regional Geology and Petroleum Resources. Scientific Press Ltd., 292 p. BP 2006. Quantifying energy. BP statistical review of world energy, June 2006. BP, London, 45 p. Burke, R.J. and F.J. Gardner 1969. The world’s monster oil fields and how they rank. Oil and Gas Journal, v. 67, no. 2, p. 43-49. Hasson, R.C., J.F. Mason and Q.M. Moore 1975. Petroleum developments in Middle East countries in 1974. American Association of Petroleum Geologists Bulletin, v. 59, no. 10, p. 1950-1974. Hasson, R.C., J.F. Mason and Q.M. Moore 1976. Petroleum developments in Middle East countries in 1975. American Association of Petroleum Geologists Bulletin, v. 60, no. 10, p. 1865-1899. Hasson, R.C., D.O. Hemer, J.F. Mason and Q.M. Moore 1977. Petroleum developments in Middle East countries in 1976. American Association of Petroleum Geologists Bulletin, v. 61, no. 10, p. 1795-1829. Hasson, R.C., D.O. Hemer, J.F. Mason and Q.M. Moore 1978. Petroleum developments in Middle East countries in 1977. American Association of Petroleum Geologists Bulletin, v. 62, no. 10, p. 2111-2149. Hemer, D.O., R.C. Hasson, J.F. Mason and Q.M. Moore 1979. Petroleum developments in Middle East countries in 1978. American Association of Petroleum Geologists Bulletin, v. 63, no. 10, p. 1884-1914. Hemer, D.O., J.F. Mason and G.C. Hatch 1981. Middle East. American Association of Petroleum Geologists Bulletin, v. 65, no. 10, p. 2134-2161. Hemer, D.O., J.F. Mason and G.C. Hatch 1982. Oil and gas developments in Middle East in 1981. American Association of Petroleum Geologists Bulletin, v. 66, no. 11, p. 2011-2033. Hemer, D.O and G.C. Hatch 1983. Oil and gas developments in Middle East in 1982. American Association of Petroleum Geologists Bulletin, v. 67, no. 10, p. 1698-1716. Hemer, D.O and P.J. Pickford 1984. Oil and gas developments in Middle East in 1983. American Association of Petroleum Geologists Bulletin, v. 68, no. 10, p. 1413-1429. Hemer, D.O and J.H. Lyle 1985. Oil and gas developments in Middle East in 1984. American Association of Petroleum Geologists Bulletin, v. 69, no. 10, p. 1727-1743. Hotchkiss, H. 1960. Petroleum developments in Middle East and adjacent countries in 1959. American Association of Petroleum Geologists Bulletin, v. 44, no. 7, p. 1144-1178. Hotchkiss, H. 1961. Petroleum developments in Middle East and adjacent countries in 1960. American Association of Petroleum Geologists Bulletin, v. 45, no. 7, p. 1186-1223. Hotchkiss, H. 1962. Petroleum developments in Middle East and adjacent countries in 1961. American Association of Petroleum Geologists Bulletin, v. 46, no. 7, p. 1241-1280. Hotchkiss, H. 1963. Petroleum developments in Middle East and adjacent countries in 1962. American Association of Petroleum Geologists Bulletin, v. 47, no. 7, p. 1397-1436. Hotchkiss, H. 1964. Petroleum developments in Middle East and adjacent countries in 1963. American Association of Petroleum Geologists Bulletin, v. 48, no. 8, p. 1345-1386. Hotchkiss, H. 1965. Petroleum developments in Middle East countries in 1964. American Association of Petroleum Geologists Bulletin, v. 49, no. 8, p. 1292-1329. Insalaco, E., A. Virgone, B. Courme, J. Gaillot, M. Kamali, A. Moallemi, M. Lotfpour and S. Monibi 2006. Upper Dalan/Kangan Formation between the Zagros Mountains and offshore Fars: depositional system, biostratigraphy and stratigraphic architecture. GeoArabia, v. 11, no. 2, p. 75-176. International Energy Agency (IEA) 1995. Middle East Oil and Gas. Organisation for Economic Co-operation and Development (OECD), France, 413 p. Kamen-Kaye, M. 1970. Geology and productivity of Persian Gulf synclonorium. American Association of Petroleum Geologists Bulletin, v. 54, no. 12, p. 2371-2394. Klett, T.R. and J.W. Schmoker 2003. Reserve growth of the world’s giant oil fields. In, M.T. Halbouty (Ed.) Giant oil and gas fields of the decade 1990-19999. American Association of Petroleum Geologists Memoir 78, p. 107-122. Lynch, M 2006. Letter to the Editor. Petroleum Review, v. 60, no. 713, p. 15. Mann, P., L. Gahagan and M.B. Gordon 2003. Tectonic setting of the world’s giant oil and gas fields. In, M.T. Halbouty (Ed.) Giant oil and gas fields of the decade 1990-19999. American Association of Petroleum Geologists Memoir 78, p. 15-105. Mason. J.F. 1967. Petroleum developments in Middle East countries in 1966. American Association of Petroleum Geologists Bulletin, v. 50, no. 8, p. 1741-1760.

Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/12/2/69/4570022/husseini.pdf by guest on 24 September 2021 Al-Husseini

Mason. J.F. and Q.M. Moore 1967. Petroleum developments in Middle East countries in 1966. American Association of Petroleum Geologists Bulletin, v. 51, no. 8, p. 1626-1648. Mason. J.F. and Q.M. Moore 1968. Petroleum developments in Middle East countries in 1967. American Association of Petroleum Geologists Bulletin, v. 52, no. 8, p. 1552-1573. Mason. J.F. and Q.M. Moore 1969. Petroleum developments in Middle East countries in 1968. American Association of Petroleum Geologists Bulletin, v. 53, no. 8, p. 1764-1788. Mason. J.F. and Q.M. Moore 1970. Petroleum developments in Middle East countries in 1969. American Association of Petroleum Geologists Bulletin, v. 54, no. 8, p. 1524-1547. Mason. J.F. and Q.M. Moore 1971. Petroleum developments in Middle East countries in 1970. American Association of Petroleum Geologists Bulletin, v. 55, no. 9, p. 1603-1630. Mason. J.F., Q.M. Moore and R.C. Hasson 1972. Petroleum developments in Middle East countries in 1971. American Association of Petroleum Geologists Bulletin, v. 56, no. 9, p. 1793-1819. Mason. J.F., Q.M. Moore and R.C. Hasson 1973. Petroleum developments in Middle East countries in 1972. American Association of Petroleum Geologists Bulletin, v. 57, no. p. 10, 2057-2084. Mason. J.F., R.C. Hasson and Q.M. Moore 1974. Petroleum developments in Middle East countries in 1973. American Association of Petroleum Geologists Bulletin, v. 58, no. 10, p. 2101-2122. McDonald, P. 2006. Oil production outlook means Iran may need nuclear power. Petroleum Review, April, p. 20-23. MEES 24 November 2003. Iran reveals end-1999 reserves breakdown for oil and condensate fields. Middle East Economic Survey, v. 46, no. 47, p. D5-D9. MEES 1 December 2003. Iran declares reserves additions in producing fields. Middle East Economic Survey, v. 46, no. 48, p. A10-A11. MEES, 1 August 2005. Iranian production capacity now 4.2 Mn B/D, Zanganeh confirms. Middle East Economic Survey, v. 48, no. 31, p. 15. MEES 13 February 2006. Iran’s petroleum industry: what’s at stake if the nuclear standoff becomes a crisis. Middle East Economic Survey, v. 49, no. 7, p. 3-5. MEES, 5 June 2006. Iran targeting oil output capacity of 4.6Mn B/D by 2009, says Vaziri-Hameneh; NIOC plans 100 new development wells in Ahwaz field. Middle East Economic Survey, v. 49, no. 23, p. 15. MEES, 19 June 2006. Norsk Hydro announces commerciality of Azar field. Middle East Economic Survey, v. 49, no. 25, p. 15-16. MEES, 18 September 2006. Vaziri-Hamaneh confirms Iran’s reservoir decline amounts To 500,000 B/D per year. Middle East Economic Survey, v. 49, no. 38, p. 12-13. NIOC, National Iranian Oil Company 1998. Conference in London, June 30 to July 2, 1998. GeoArabia, 1998, v. 3, no. 3, p. 439–455. Organization of the Petroleum Exporting Countries (OPEC) 1994. Annual Statistical Bulletin. 137 p. Petroleum Economist 1996. Middle East and Africa, Volume IV. World Oil Fields and World Gas Fields Series. United Kingdom, 101 p. Petroleum Review 2006. Prices holding steady, despite massive planned capacity additions. April, p. 28-31. Schlumberger 2003. Islamic Republic of Iran, Reservoir Optimization Conference. Schlumberger, 137 p. Stöcklin, J. and O. Setudehnia 1972. Iran. Lexique Stratigraphique International, v. III, Asie, L. Dubertret (Ed.), CNRS, Paris, 376p. Szabo, F. and A. Kheradpir 1978. Permian and Triassic Stratigraphy, Zagros Basin, South-West Iran. Journal of Petroleum Geology, v. 1, p. 57-82.

ABOUT THE AUTHOR

Moujahed I. Al-Husseini founded Gulf PetroLink in 1993 in Manama, Bahrain. Gulf PetroLink is a consultancy aimed at transferring technology to the Middle East petroleum industry. Moujahed received his BSc in Engineering Science from King Fahd University of Petroleum and Minerals in Dhahran (1971), MSc in Operations Research from Stanford University, California (1972), PhD in Earth Sciences from Brown University, Rhode Island (1975) and Program for Management Development from Harvard University, Boston (1987). Moujahed joined Saudi Aramco in 1976 and was the Exploration Manager from 1989 to 1992. In 1996, Gulf PetroLink launched the journal of Middle East Petroleum Geosciences, GeoArabia, for which Moujahed is Editor-in-Chief. Moujahed also represented the GEO Conference Secretariat, Gulf PetroLink-GeoArabia in Bahrain from 1999-2004. He has published about 30 papers covering seismology, exploration and the regional geology of the Middle East, and is a member of the AAPG, AGU, SEG, EAGE and the Geological Society of London. [email protected]

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