The oil and gas plays found in Angola range from the pre-salt to the post-salt and include Tertiary-age clastic turbidite reservoirs, salt-rafted Cretaceous age Pinda carbonates, and pre-salt microbalitic carbonates similar to Brazil’s giant Tupi oil discovery. Many of these have only been identified since the turn of the new century, and these wide-ranging, high potential plays have led to a dramatic surge in Angola’s oil production.
A decade ago, the country was producing approximately 750,000 bopd, while now production of almost 2 MMbopd has been achieved. Angola is already the second biggest oil producer in Africa after Nigeria (which is currently producing about 2.4 MMbopd), but its highly favourable petroleum geology means that within the next decade it is expected to replace that country as Africa’s top oil producer.
The first milestone in Angola’s petroleum industry occurred in the late 1700s when the Portuguese colonialists discovered oil seeps and asphalt deposits at Libongos, about 60 km north of Luanda, and shipped some of the oil to Lisbon and Rio de Janeiro to be used as caulking material to prevent water leakage into their ships. Libongos is located on the eastern edge of the Kwanza Basin, within half a kilometre of outcrops of Precambrian granites.
The year 1915 marked the next important milestone for Angola when the Portuguese oil company, Companhia de Pesquisias Mineras de Angola, carried out the first drilling for oil in the valley of the Dande River, near the coastal village of Barra do Dande, about 40 km north-east of Luanda. One of the wells, Dande-4, drilled in 1916, was tested at 6 bopd and was subsequently abandoned, but it signified the first flow of oil in Angola.
Drilling for oil in the onshore Kwanza Basin continued sporadically for the next forty years but with no commercial success until 1955, when the Benfica-2 well just south of Luanda resulted in the first commercial oil discovery in Angola. The field went on production in 1956, representing the beginning of oil production in Angola. The first offshore oil field in Angola, Malongo, was discovered ten years later in 1968 in Cabinda by the American company, Cabinda Gulf Oil Company. Chevron bought Gulf Oil in the early 1980s and the company is still an operator, now producing approximately 500,000 bopd from just two blocks offshore Cabinda.
Angola’s long-drawn-out civil war, which lasted from independence in 1975 until 2002, undoubtedly slowed down onshore exploration, so international companies concentrated on the offshore during these years. Angola was producing about 700,000 bopd by 1996 when another historic event happened: the French oil company Elf Petroleum discovered the Girassol oil field in Block 17 in deep waters (1,300m), about 140 km off the coast of Angola. This discovery stunned the oil industry, since finding oil so far from the coast and in a new geological formation was totally unexpected. Additional drilling by Elf proved Girassol to be a giant size field, with the oil-bearing reservoir located in Oligocene sandstones and conglomerates which had been deposited as turbidites. This led to many more such discoveries in the Oligocene and Miocene (15 Ma) in the deep waters off Angola, including by Chevron, Esso, Maersk, Total, BP and Sonangol P&P. As a result, about 75% of Angola’s production now comes from such reservoirs. Had Girassol and the follow-up fields not been discovered, Angola would have remained merely a modest oil-producing country with production of only about 500,000 bopd – now it is an important one.
Looking Across the Atlantic
The discovery of the Tupi oil field on the other side of the southern Atlantic in Brazil in 2007 was an historic event for the oil industry. Tupi was drilled by Petrobras in the deepwater part of the Santos sedimentary basin in water depths of 2,100m. It was drilled to a depth of about 5,200m below the sea floor, giving a total drill depth of the well of 7,300m; it had many mechanical problems and the final cost was $240 million. But the costs were justified by the results. Tupi is estimated to hold eight billion barrels of recoverable oil reserves in a high pressure, high temperature environment beneath a massive salt sheet over 2,000m thick. Tupi (now renamed Lula after Brazil’s ex-President Lula) proved to be the first of the now famous pre-salt oil and gas fields which have been found in the Santos Basin as well as in the more northerly Campos Basin in Brazil.
The Tupi discovery proved that a working petroleum system exists beneath the salt layer of the Santos Basin. The oil source rocks are the organically rich lake shales, the reservoirs are lake beach sands and porous limestones and dolomites known as microbalites, and the seal above the reservoirs which keeps the oil entrapped is the thick, impervious salt layer. Oil industry analysts such as Wood Mackenzie and IHS have estimated that the oil reserves in Brazil’s pre-salt reservoirs could amount to some 20 to 30 Bbo recoverable, with ANP, Brazil’s government oil industry regulatory agency, quoting recoverable reserves of up to 50 Bbo. The impact of these discoveries has been dramatic: Brazil’s oil production is now at a record 2.2 MMbopd of which already about 150,000 bopd is from the pre-salt. Petrobras recently announced that output from the pre-salt reserves is expected to grow, bringing Brazil’s per-day oil output to 6 MMbo, nearly triple current production.
When the conjugate margins of Angola and Brazil are juxtaposed or reconstructed to the time of the initial opening of the southern Atlantic, about 140 million years ago in the early Cretaceous, the Santos and Campos Basins are clearly located adjacent to Angola’s Benguela and Kwanza Basins. Accordingly, the success in the pre-salt of Brazil could be repeated in Angola’s deepwater areas, where drilling in the pre-salt was negligible before 2011.
“If you are a petroleum geoscientist, you’ll be challenged to find a country as interesting as Angola”
More History is Made
As a result of investigating the southern Atlantic conjugate margins, an historic event for the hydrocarbon industry in Angola occurred in 2011 when eleven deep to ultra-deepwater pre-salt blocks in the Kwanza and Benguela Basins were awarded by Sonangol to a number of operators. These included BP, Cobalt, Repsol, Total, Eni, ConocoPhillips and Statoil, the last obtaining the lion’s share with two operated blocks and non-operated working interests in three others (
see GEO Expro, Vol. 5, No. 4). On 4 January this year Maersk and Sonangol announced that Azul-1 on deepwater Block 23 was the first well to penetrate pre-salt objectives in Angolan deepwater. The well was drilled in a water depth of 920m and reached a total depth of 5,330m. The press release stated that “the preliminary interpretation of the data indicated a potential flow capacity of greater than 3,000 bopd. We are encouraged by the results of our first pre-salt exploration well in this region, which was also the first ever deepwater well targeting pre-salt reservoirs in the Kwanza Basin”.
Shortly afterwards, on 9 February 2012, Cobalt International Energy (CIE) announced the results of its Cameia-1 well, drilled in 1,680m of water in deepwater Block 21, again targeting the pre-salt section. Cobalt reported that the well confirmed the presence of 360m of gross continuous oil column with over a 75% net to gross pay estimate. No gas-oil or oil-water contact was evident on the wireline logs. An extended DST (drill stem test) was performed on Cameia-1 which flowed at a sustained rate of 5,010 bpd of 44° API oil and 14.3 MMcfpd of associated gas, giving a total of approximately 7,400 boepd day with limited drawdown. Cobalt stated that it believes that the well has the potential to produce in excess of 20,000 bopd.
What Does the Future Hold?
Based on my 40 years of experience in the oil industry, I expect that the Angolan oil industry will remain vital for many more years. Already, two-thirds of Angola’s production is from the deepwater and, unquestionably, more Oligocene and Miocene oil discoveries will be made in the ultra-deepwater areas seawards of Blocks 31, 32 and 33. Based on the drill results of Maersk’s and Cobalt’s wells, the pre-salt play suddenly looks very promising.
Could the dramatic increase in production seen in Brazil as a result of the discovery of the pre-salt oil fields happen to Angola? Based on the very recent successes by Maersk and Cobalt, it is possible, although, of course, much more drilling is needed.
Another milestone in Angola’s petroleum industry will happen in June 2012 when the LNG plant at Soyo in northern Angola commences production at 5.2 MM tonnes per year. On an energy-equivalent basis, this amounts to about 200,000 barrels of oil per day. A strong demand exists for Angola’s natural gas due to the increasing consumption of LNG in Asia and also as Europe seeks to reduce its reliance on gas from Russia. In addition, as gas becomes increasingly the preferred fuel of the future, there will be much focus on the gas potential in Angola, which to date has been only minimally explored.
Tako Koning is a long time resident of Angola. Born in Holland and raised in Canada, he is a geologist who started his career forty years ago working with Texaco in Canada, followed by assignments to a number of countries, including Indonesia and Nigeria. Since 1995 he has been living and working in Angola, where he combines being a consultant in Luanda for Gaffney, Cline and Associates with leading field trips in the country. He has published more than 100 papers and abstracts and in 2010 was awarded the AAPG’s Public Service Award for a lifetime of mixing humanitarian aid with his science on a global basis.