Print this page 
Click to view presentation
in PDF format.
Saharan Africa — a Century of Exploration, What to Expect?*
James D. Veron1 and Mohamed Zine1
Search and Discovery Article #40429 (2009)
Posted June 16, 2009
*Adapted from expanded abstract prepared for AAPG International Conference and Exhibition, Cape Town, South Africa, October 26-29, 2008.
1IHS, Perly-Geneva, Switzerland ([email protected])
Petroleum exploration in Africa commenced at the end of the 19th century and was first characterised by the drilling of wells close to oil seeps in Egypt. Since the first oil discovery in 1907, more than 3,900 2D seismic and 600 3D seismic surveys have been undertaken in Saharan Africa, resulting in the acquisition of over 1.8 million line-km of 2D and some 320,000 sq km of 3D. Almost 7,000 new-field wildcats have been drilled and 1,700 discoveries were made. Saharan Africa is a proven giant in terms of hydrocarbon production and export. Ultimate recoverable reserves are estimated at 106 Bb of liquids and 380 Tcf of gas. The recent discoveries do not offset the oil and gas production but many basins remain immature to moderately mature in terms of hydrocarbon exploration. Saharan Africa is considered as having a great potential but the question is how much is there still to be discovered? One way of evaluating the remaining reserves is to use complex models, but what can previous exploration phases and statistics indicate to us? With field size distribution and Yet-To-Find (YTF) methods we can attempt to provide an estimate and the distribution of remaining recoverable hydrocarbon reserves. For Saharan Africa, estimated YTF oil reserves range from 15 to 27 Bb while YTF gas reserves range between 57 and 67 Tcf. The parabolic YTF method applied basin by basin suggests that up to 40 Bboe are still to be discovered in existing plays in Saharan Africa. The empirical YTF analyses can be interpreted as very conservative as these statistical methods are not applicable in frontier basins, non-conventional resources are not included and no allowance was made for reserves growth. In addition, our understanding of the Saharan Africa geology will improve along with new studies, adding new plays and therefore reserves.
uResource Replacement and Non-Developed Discoveries
uResource Replacement and Non-Developed Discoveries
uResource Replacement and Non-Developed Discoveries
uResource Replacement and Non-Developed Discoveries
uResource Replacement and Non-Developed Discoveries
uResource Replacement and Non-Developed Discoveries
|
Petroleum exploration in Africa commenced at the end of the 19th century and was first characterised by the drilling of wells close to oil seeps in Egypt. Since the first oil discovery in 1907, more than 3,900 2D seismic surveys and 600 3D seismic surveys have been undertaken in Saharan Africa, resulting in the acquisition of over 1.8 million line-km of 2D seismic data and some 320,000 sq km of 3D seismic data. Almost 7,000 new-field wildcat wells have been drilled and 1,700 discoveries were made.
Saharan Africa has proven extremely prospective for oil and gas and the region is a proven giant in terms of hydrocarbon production and export. Ultimate recoverable reserves are estimated at some 106,000 MMb of liquids and over 380 Tcf of gas. The recent discoveries do not offset the oil and gas production but many basins remain immature and moderately mature in terms of hydrocarbon exploration. Saharan Africa can therefore still be seen as a rare frontier area for oil and gas exploration.
Approximately 14 million sq km are considered as prospective and some 6.5 million sq km are licensed, with permit size ranging from 0.9 sq km (SAR 1 Concession in Morocco) to 288,500 sq km (Block 14 in Sudan). The entry of new players such as Asian NOCs, has however made some African opportunities much more expensive. Algeria is still courted by many European countries for mega-projects while the re-integration of Libya into the international community is ongoing.
The region saw a burst in exploratory drilling since 2003. Until only recently, few exploration wells were drilled but with deeper objectives and higher success rates. This reflects both the use of modern technologies and the in-depth knowledge of the region. The combination of high prices, big profit potential and growing gas markets set off a worldwide gas-exploration boom. The number of major oil discoveries is declining, while the opposite is true for gas.
Resource Replacement and Non-Developed Discoveries
Resource replacement in Saharan Africa is decreasing but not as dramatically as in some other regions (Figure 1). In 2006, Saharan Africa produced some 5.3 MMbo/d, slightly less than 2 billion BO a year, and 16,868 MMcfg/d. Over 10 years, only Sudan is increasing its (remaining) oil reserves, coming from spectacular finds in Melut and Muglad basins. Egypt has increased its gas reserves by over 60 Tcf in the last 10 years, but gas production has also risen spectacularly in Egypt and in Algeria. The latter is producing more gas than is being found.
Almost half of the discoveries remain undeveloped due to above ground reasons (strategic and commercial) and below ground reasons (technical, volume and costs) (Figure 2). Looking at the size of these undeveloped discoveries, it is obvious that many small discoveries are unlikely to be developed, but that a few large undeveloped discoveries may come on stream in the near future.
As for gas, Sonatrach wishes to create a new gas hub in southwestern Algeria (Reggane and Timimoun Basins), combining the development projects of companies having made discoveries in the area, e.g. GdF, Repsol, Shell and Total. The main economical issues with such development project are the geographical dispersion of the gas discoveries and the relatively high CO2 content (around 6 to 8%) in the gas discovered. The Trans-Saharan Gas Pipeline mega-project may also boost gas exploration and development in the area of concern. Feasibility studies by GdF and Petronas are ongoing for gas export and local power generation from gas in Mauritania.
Libya government objective is to move forward to be a key supplier LNG to Southern Europe and North America. A big exploration campaign is launched in the Sirte Basin. Assuming sufficient gas is found the Marsa El Braga plant capacity will be upgraded and if more gas is found a new LPG plant will be added. The LNG currently produced at Marsa El Braga is shipped to Spain.
Saharan Africa is considered as having a great potential but the question is how much is there still to be discovered? One way of evaluating / calculating the remaining reserves is to use complex models including reservoir distribution, source rock richness and distribution, production index, etc. But what can previous exploration phases and statistics indicate to us?
The yet-to-find parabolic method for oil suggests that over 10 Billion barrels of oil are still to be discovered in Saharan Africa.
In this study, two scenarios using different equation variables for the parabolic distribution are here presented for gas reserves. A high scenario taking account all fields and a low scenario considering a King Effect due to the super giant Hassi R'Mel field were carried out. The high gas scenario indicates that almost 300 fields with reserves in excess of 150 Bcfg are to be discovered. The low gas scenario clearly underestimates the total gas reserves in the basin, but it has the advantage of not focusing on the Hassi R'Mel field reserves.
The parabolic yet-to-find method applied basin by basin suggest that up to 40 Billion barrels of oil equivalent are still to be discovered in existing plays in Saharan Africa.
The oil field size distribution graph suggests that approximately 8,000 MMbo are still to be discovered in fields with reserves of over 50 MMbo. The gas field size distribution graph suggests that some 17 Tcfg are still to be discovered in fields with reserves of at least 600 Bcfg. (Figure 3)
Despite over a century of oil & gas exploration, many basins in Saharan Africa remain immature and moderately mature in term of hydrocarbon exploration. The yet-to-find methods can't be used for the frontier areas that are briefly discussed below.
Algeria - The gas-rich Reggane-Timimoun area is still relatively unexplored and recent successes in the area suggest a great potential. The complex geological setting of northern area makes it difficult to assess its hydrocarbon potential. Libya - Very little activity has been performed in the Al Kufra Basin, South of Murzuq Basin, the Pelagian Basin and the offshore extension of Sirte Basin. No positives results have been made yet. Some five high impact wells are planned in late 2008 and in 2009. That is a critical period for Libya promising potential outside the proven basin.
Egypt - As yet exploration effort has been very limited in the Upper Egypt region. Basins are generally shallow and little more than troughs or localised depressions. In view of the limited and scanty knowledge gained to date, the overall exploration potential of the area remains low, with perhaps the most promising targets being in the Paleozoic and Jurassic, particularly in the west and southwest of the region and in the Nile Delta deep offshore.
Ethiopia- The area is still at an early exploration stage, with a proven hydrocarbon province (Ogaden) and two frontier areas (Southern Rift and Adigala) currently under exploration.
Mauritania/Mali - The Taoudeni is the largest intracratonic basin in Africa, covering some 1.3 million sq km, but only six wells have been drilled. In Mali, Elf's Yarba recorded gas shows and some dead oil in 1982, while Esso's Atouila 1 recorded insignificant gas shows. In Mauritania, Agip's Ouasa 1 was p&a dry in 1974. The same year, Texaco's Abolag 1 tested 0.48 MMcfg/d with condensate and salt water. Some 30 years later, majors are revisiting the Taoudeni Basin and wildcats are scheduled for early 2009.
Intra-rift basins - Almost all the Central African rift basins are currently covered by licences but only 330 wildcats have been drilled. In Chad and Sudan, the first discoveries were made in the late 1970s and early 1980s, respectively, but political impediments have hindered hydrocarbon exploration. Activity nevertheless resumed in the last decade resulting in the development of the major fields and the discovery of some 3,000 MMbo in the Melut and Muglad basins. Similar success may be expected in the other intracratonic basins. (Figure 4)
The empirical yet-to-find analyses suggest that several billion barrels of oil and trillion cubic feet of gas are still to be discovered in the main hydrocarbon provinces that are Algeria, Libya and Egypt. Large discoveries are to be found in Sudan, and several large areas, such as the Taoudeni Basin, may hold significant hydrocarbon resources.
Accepting that no field larger than Hassi R-Mel can be discovered in Saharan Africa, total undiscovered gas reserves are estimated to range between 57 Tcf and 67 Tcf. Estimated yet-to-find oil reserves range from 14,000 MMb to 26,000 MMb. Our estimation of undiscovered recoverable reserves for Saharan Africa may not include economic factors, but as it was carried out using mainly productive field sizes, the order of magnitude of the recoverable reserves should prove to be appropriate. The economic threshold will change with time and our understanding of the Saharan Africa geology will also improve along with new studies, adding new plays and therefore reserves.
The yet-to-find results can be interpreted as very conservative as these statistical methods are not applicable in frontier basins. A minimum of four discoveries are required in order to estimate the yet-to-discover fields. The hydrocarbon potential of poorly explored basins, such as the Taoudeni Basin, cannot yet be assessed with such methods. In addition, no allowance was made for reserves growth and non-conventional resources are not included.
|
