Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 Introduction DUNCAN S. MACGREGOR BP Exploration Operating Co. Ltd, Kuningan Plaza, S. Tower, P.O. Box 2749, Jakarta 12940, Indonesia This Special Publication of the Geological 'booked' in Algeria in 1994 than in any other Society documents a series of papers collected country in the world. on the petroleum geology of Morocco, Algeria, The importance of the region to the petroleum Tunisia, Libya and the western part of Egypt. industry is, of course, not reflected in the volume This region contains some 4% of the world's of geological literature available on the area, par- remaining oil and gas reserve (Table 1), placing ticularly that in English. This volume represents the area above more traditional producing the first such attempt at a compilation of the pet- regions, including Europe, the USA and SE roleum geology of this region. The main objec- Asia, in its importance as a future petroleum pro- tives of this book are thus to increase the level ducer. In addition to these considerable proven of documentation towards that appropriate for reserves, North Africa is now one of the world's such major petroleum provinces and to facilitate most active exploration areas. This was reflected, the application of analogues between North Afri- for instance, in more new oil reserves being can countries and beyond. Table 1. North African petroleum reserves and their global significance Rank Country Reserves (109 BBO) Oil reserves (remaining) 1 Saudi Arabia 261.2 2 Iraq 100.0 3 United Arab Emirates 98.1 4 Kuwait 96.5 5 Iran 88.2 6 Venezuela 64.5 7 Mexico 49.8 8 Russia* 49.0 9 USA* 29.6 10 Libya 29.5 (2.9% of world total) 11 China 24.0 12 Nigeria 20.8 13 Algeria* 9.2 (0.9% of world total) - Egypt (inc. Gulf of Suez) 3.9 (0.4% of world total) - Tunisia 0.4 ( <0.1% of world total) Rank Country Reserves (1012 SCF) Gas reserves (remaining) 1 Russia* 1700 2 Iran 742 3 Oman 250 4 United Arab Emirates 205 5 USA* 164 6 Venezuela 140 7 Algeria* 128 (2.6% of world total) 8 Nigeria 110 9 Iran 110 10 Indonesia 69 19 Libya 46 (0.9% of worm total) - Egypt (inc. Gulf of Suez) 22 (0.4% of world total) *Areas with significant Palaeozoic-Triassic reservoired component to reserves. Source: BP Statistical Review of Worm Energy, 1996, data as at end 1995. BBO, Billion barrels of oil; SCF, stan- dard cubic feet. MACGREGOR,D. S. 1998. Introduction. In: MACGREGOR,D. S., MOODY,R. T. J. & CLARK-LOWES,D. D. (eds) 1998. Petroleum Geology of North Africa. Geological Society, London, Special Publication No. 132, 1-6. Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 2 D.S. MACGREGOR It has been our mission, in seeking papers for category. Overview papers are presented for this volume, to try to obtain a full and represen- each of the two stratigraphic sections thus tative set of papers covering different regions and defined and are followed in each case by regional themes. Thus we sought both full coverage of the papers, covering topics such as petroleum sys- stratigraphic column (Fig. 1) and as wide as pos- tems, stratigraphy and regional structure, and sible geographical coverage (Fig. 2). Particular those relating to individual reservoirs, fields encouragement was given to authors from and play fairways. Because of its unique struc- North Africa to submit previously unpublished tural history and play types, the Atlas region is material on the oilfields and gas fields of the assigned a separate sub-section within the Meso- region. In this regard, we particularly acknowl- zoic-Cenozoic category. The Gulf of Suez and edge the contribution from Sonatrach, which, Nile Delta petroleum provinces are not strictly with six papers, is overwhelmingly the predomi- included in the region covered by this book, nant contributor to the volume. but are touched on in some papers, particularly As the aims of this book are to encourage the that by Keeley & Massoud. use of analogues over national boundaries, we have avoided grouping the papers geographi- cally. Instead, we have first split the papers stra- Palaeozoic and sub-salt tigraphically into 'Palaeozoic and sub-salt' and 'Mesozoic-Cenozoic' sections (Fig. 2). This divi- The North Africa region is perhaps best known sion is justified both by the structural history of in international geological circles for its Palaeo- the area, which would suggest a partition at the zoic reservoirs and source rocks (Figs 1 and 3). Hercynian unconformity (Fig. 3), with a modifi- The Palaeozoic and sub-salt contribute nearly cation to this boundary suggested by reviewing half the oil (43%) and the vast majority (84%) source-reservoir associations, such that discus- of the gas reserves of the region (Figs 4 and 5), sions on the sub-salt Triassic reservoir of Algeria with most of this petroleum originating from are most rationally included in the 'Palaeozoic' Silurian and Devonian source beds (Fig. 3). Fig. 1. Chronostratigraphy of the Phanerozoic of the main North African petroleum provinces, as compiled from various papers in this volume. The most significant oilfields, reservoirs and source rocks are labelled. Papers in this volume are split into those pertinent to the petroleum systems below the salt in the west of the region and those on the Mesozoic systems in the east of the region. (For line of section, see Fig. 2.) Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 INTRODUCTION 3 Fig. 2. Geographical coverage of the papers in this volume. The main petroleum basins are stippled and numbered as follows: 1, Ahnet; 2, Oued Mya; 3, Ghadames; 4, Illizi; 5, Gabes-Pelagian; 6, Sirt; 7, Abu Gharadiq; 8, Murzuq. Fig. 3. Composite petroleum system diagram for the North African provinces. The boxes are sized according to the relative importance of the various reservoirs, source rocks and events. It is possible to differentiate two main plate tectonic cycles, Cambrian to Carboniferous and Triassic to Recent, which are also reflected in cycles of petroleum generation, entrapment and destruction. *Existing hydrocarbon-bearing traps only. Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 4 D. S. MACGREGOR giant fields that may still lie undiscovered in this region. Fekirine & Abdallah concentrate on the stratigraphic development and sequence stra- tigraphy of the Algerian Palaeozoic, work which emphasizes the unusually strong role that eustasy plays in controlling facies development in this cratonic area. A complementary paper by Echikh attempts a similar understanding of the Ghadames Basin; this study extends into Libya and notes a number of key differences with the parts of Algeria reviewed by Fekerine & Abdal- lab, particularly the more significant role of the Fig. 4. Pie chart illustrating distribution of oil reserves Caledonian event in the Ghadames area. The amongst the main reservoir fairways of North Africa. The predominance of Mesozoic-Cenozoic reservoirs extension of the Palaeozoic petroleum systems should be noted. productive in Ghadames and Illizi into the fron- tier basins to the west is the subject of a paper by Logan & Duddy, who emphasize the significance in these areas of timing of generation relative to trap formation. This paper emphasizes the con- tribution that modern techniques, in this case apatite fission track analysis, can make to fron- tier exploration in North Africa. The interpreta- tion by these authors of a late-stage heating event of large regional extent is one which has major significance for our view of the prospectivity of western Algeria. Cambro-Ordovician clastic reservoirs contri- bute 26% of the oil and 13% of the gas in North Africa (Figs 4 and 5), with the region having higher reserves in rocks of this age than Fig. 5. Pie chart illustrating distribution of gas reserves any other region of the world. Crossley & amongst the main reservoir fairways of North Africa. McDougall open the review of Palaeozoic reser- The predominance of Palaeozoic and Triassic voirs by summarizing some of the key points con- reservoirs should be noted. The more gas-prone nature trolling reservoir quality and distribution in the of these reservoirs is related to the state of maturity of Lower Palaeozoic, based on literature and their Palaeozoic source and rocks, and timing relationships own outcrop studies in Morocco. These authors between that maturity and the formation of traps. also emphasize the potential for subtle trap dis- coveries in the future, on grounds independent of those used by Macgregor. Most of the Cambro-Ordovician reserves lie in a single field, Hassi Messaoud. The controls on With the exception of the Amal and a few asso- the producibility of these reservoirs in the area ciated fields in the Sirt Basin (Gras & Thnsu), of that field are reviewed by Djarnia & Fekirine. Palaeozoic production comes almost exclusively This work illustrates the importance of clay from the western part of the region, particularly mineralogy as a control on permeability, and Algeria (Figs 1 and 2). Boote et al. open this sec- identifies relationships to clay type and content tion with a comprehensive overview of Palaeo- similar to those described in the Rotliegendes zoic petroleum systems, based on a series of of the Southern North Sea. detailed play maps delineating the main produ- The clastic section ranging from latest Silurian cing plays in the Cambro-Ordovician, Early to Early Carboniferous delivers 11% of North Devonian and Triassic, sourced mainly from African oil and 13% of gas (Figs 4 and 5), with the Early Silurian and Late Devonian. Traut et most of this contribution coming from the al.