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From: Semirnna Adhanom (semirnna@yahoo.com)
Date: Thu Oct 14 2010 - 18:32:38 EDT
"New Geography" - An Underexplored Salt Province
Thursday, September 30, 2010
A thirty year independence struggle with Ethiopia means that the natural
resources of Eritrea remain largely untapped, but there is ample evidence that
this now peaceful country is highly prospective for oil and gas.
By Jane Whaley , OilEdge
The Dahlak Islands in the Red Sea, where oil seeps encouraged exploration in the
1920’s. They have been famous for pearl fishing since Roman times Photo: Boris
Kessler
Like many of us, when Eritrea was first mentioned to Alec Robinson, he reached
for the atlas. “It’s not the first place that springs to mind when thinking of
African hydrocarbon exploration,” the CEO of Centric Energy admits. “But that’s
the point. It’s one of the few relatively unexplored places left in the world –
and it has great potential. The Eritrean Red Sea has all the classic features of
pre- and post-rift sedimentation, including syn-rift evaporites, as well as a
known oil-rich source, and sediment feeder channels leading to prospects in less
than 50m of water. There are also oil seeps on the islands of the Dahlak
archipelago, and along the coast.”
“In addition to all the positive geological indicators,” Alec adds, “it is now
one of the safest and most peaceful places to work in Africa. The government has
made great efforts to encourage oil companies to the country.
The geology of Eritrea is dominated by metamorphosed Precambrian rocks, which
were deformed by the pan-African orogeny, and then further altered by the
intrusion of Lower Palaeozoic granites. As a result, the country abounds in
minerals such as gold, copper, and zinc, but most of the areas prospective for
hydrocarbons are found offshore.
“... one of the safest and most peaceful places in Africa”
Most of the hydrocarbon potential of Eritrea lies in its 16,600 km2 Red Sea
acreage. Image: NASA
Alec Robinson is a petroleum geologist who has spent nearly 40 years in the oil
industry, many of them with Amoco. He has lived and worked in many parts of the
world, including Colombia, Peru, Oman, Norway and Argentina. Now based in the
UK, he has been President and CEO of Centric Energy since 2006. Photo: Jane
Whaley
Massive gas blow-out
Eritrea lies at the southern end of the Red Sea, which was formed in
Oligo-Miocene times (36 – 20 million years ago) as the African land mass broke
away from the Arabian shield. Pre-rift arching and break-up of the continental
crust led to the formation of the Red Sea, with block faulting on the flanks and
strong subsidence in the central part, both very important for the formation of
hydrocarbon traps. As rifting continued, fluviatile and lacustrine sedimentation
was followed by shallow marine clastics and, with circulation in the Red Sea
diminishing, the deposition of evaporites. Rifting through the late Miocene was
accompanied by horst-graben faulting and fault block rotation, until by the
Early Pliocene, about 5 Ma ago, small pull-apart basins along the axis of the
Red Sea and Gulf of Aden were developing oceanic crust. These eventually
coalesced to form the passive margins found today lying on the edge of the deep
water trough of the central Red Sea, which drops rapidly to over 2,000m.
Alec and his colleagues at Centric believe that these sediments could hold large
quantities of hydrocarbons. “Although exploration started back in 1921, only
eleven wells have ever been drilled in Eritrean waters, with a further 12
shallow holes back in the 1940's on offshore islands. Eight of the offshore
wells had good oil or gas shows, and the widespread occurrence of seeps is
further evidence of a working petroleum system.”
“In fact one well, C1, drilled in 1969 by Mobil, suffered a massive gas
blow-out, and continued flowing for 55 days before finally stopping naturally.
From the limited and varying quality data available, a number of prospects and
leads have been identified in both the pre- and sub-salt formations of the
Eritrean Red Sea,” Alec says.
The Eritrean Red Sea offers potential both above and below the salt Image:
Centric Energy
Pre-and post-salt plays
As with other classic rifts, there are two distinct play types, separated by the
syn-rift evaporites. “A number of promising source horizons have been
identified, both above and below the salt,” Alec explains. “There are Late
Jurassic organic-rich shales and marls, as well as several promising source
horizons in the syn-rift, with TOCs ranging from 3% – 8%. The most recent wells,
drilled by Anadarko in 1998, also found potential source shales in the post-rift
Desset Formation.
Most of the exploration to date has centred on the post-salt plays, and
initially Centric Energy will be concentrating on these, although Alec believes
that the syn- and pre-rift plays are also very prospective. “To date, all the
seismic shot has been 2D, which has not effectively imaged the pre-salt. Modern
3D seismic is required in order to clearly delineate the sub salt horizons,”
Alec says.
Post-rift reservoirs include Neogene lenticular sandstones and reefal
limestones, with hydrocarbons trapped in structures formed by salt tectonics,
including turtle backs, rollover anticlines, fault detachments and drapes over
salt diapirs. “We believe there are also interesting stratigraphic traps, like
deepwater ponded turbidites and channel sands, which have not been investigated
yet by the drill bit.”
“The syn-rift sediments, just below the salt, are also promising – in fact, the
major blow-out in well C1 occurred just as the drilling reached this point,”
Alec continues. “While the Late Miocene formation is predominantly evaporitic in
the areas drilled so far, it includes marginal fluvial, aeolian and beach
sandstones, which may form thicker horizons as they extend into the basin. And,
of course, with all that salt, along with proven shale intervals, seal is not
expected to be a problem.”
Further potential is offered by the pre-rift, pre-salt horizons, which are
completely unexplored, although they can be visually checked at outcrop along
the coast. Plays are expected to include rotated fault blocks and horsts,
particularly in the less eroded downdip areas, with potential reservoirs
including Mesozoic fluvio-deltaic to shallow marine clastic sequences and
dolomitised limestones, and Paleozoic fluvio-glacial sandstones.
“A number of promising source horizons have been identified”
Parts of Eritrea are surprisingly green and fertile Photo: Michael
Hopley/Sunridge Gold
Why so little exploration?
Centric Energy is finalizing the terms of a Production Sharing Contract for an
offshore block and has been given exclusivity while finding a partner. At the
moment, it is the only oil company active in Eritrea, although an
Eritrean-Chinese company, Defba Oil, holds two large areas near the Sudan
border. Which begs the question: why have previous companies exploring in
Eritrea either not done more exploration or not followed up the minor
discoveries?
“Obviously, after 30 years of war, the security situation was off-putting and
left companies with concerns about operating in the country,” Alec replies. “But
there were a number of other factors. Several of the wells, particularly those
drilled in the 70’s, found gas, which at a time was not a sought-after
commodity. That is no longer an issue, as Eritrea has a clear need for
additional energy to support development - at the moment there is only one 85 MW
power station for the whole country - and there would be a definite local market
for any gas we find. In places, the presence of volcanics has resulted in
abnormally high geothermal temperatures, which deterred some explorers who did
not realise that the high geothermal gradients are localised.”
“Of course, seismic technology has only recently reached a point where we can
properly image the salt and see the horizons beneath it, opening up the
potential of the pre-rift. And it takes a little nerve to explore in a frontier
area like this, which may be easier for a smaller organisation like us.”
Centric Energy is still a very small company, having started out in 2006 as West
African Energy, focussing on West Africa with blocks in a similar rift basin in
Mali (see GEO ExPro 2008, no 4, pp26 – 30). Wanting to move further afield, it
changed its name to Centric Energy and has recently signed a production sharing
contract in Kenya.
Oil, gold – and pizza!
Eritrea is trying hard to overcome the violent historical perspective most
people hold of the country. The infrastructure is being rebuilt and efforts have
been made to develop the economy, including putting in place attractive oil and
gas licensing terms.
Sixteen foreign minerals exploration companies are now working there, reflecting
the confidence of foreign investors, and the country’s first gold mine, Bisha,
is due to start producing later this year, bringing much-needed revenue to the
country.
“It’s a great place to visit,” says Alec Robinson. “Asmara, the capital, is in
the hills, so it has a very pleasant, temperate climate, and is very safe to
walk around. The people are delightful, and don’t give you any hassle. Since it
was once part of an Italian colony, the architecture in the town is often in an
interesting sort of Italian-colonial art deco style. And they make great coffee
and pizza!”
Fascinating Cultural Fusion
Eritrea is a mostly mountainous country, bordered by Sudan, Ethiopia, Djibouti
and the Red Sea. Its Red Sea coast, 1,200 km long, is one of the hottest and
driest areas in Africa, and the Dahlak Islands, which lie just offshore, are one
of the least known or explored reefs in the Red Sea. The mountainous Central
Highlands, where the capital Asmara is located, are cooler and more fertile.
Eritrea has a rich, diverse culture, home to nine different ethnic groups. A
number of archaeological sites represent its vast and interesting history,
including the powerful Aksumite kingdom which ruled from 400 BC to 9 AD,
presiding over both sides of today’s Eritrea – Ethiopia border. It was
influenced by both Christianity, possibly through Syrian merchants, and Islam.
Later, from the 16th to the 19th century, the Ottoman Turks and the Egyptians
fought for control of the Eritrean coast and its ports, until ultimately, in the
second half of the 19th century, it became an Italian colony. By the end of the
1930’s, Eritrea was one of the most highly industrialised countries in Africa.
The British took over Eritrea after the Italian army were defeated by the Allied
forces in 1941, until 1950, when it was granted self-government within a federal
union with Ethiopia.
In 1961, Eritrea sought independence from Ethiopia, beginning Africa’s longest
conflict of the 20th century. Self-government was declared in 1993, after 32
years of struggle, only to be broken by the ‘border dispute’ in 1998, which
resulted in the death of 19,000 Eritreans. Prior to the war, most of Eritrea’s
trade was with Ethiopia, and so the country has suffered economically, with food
and energy shortages, while the large number of conflict-related deaths means
there is a shortage of manpower to re-build the economy. Two thirds of the
predominantly rural population of five and a half million receive food aid.
Despite all its troubles, Eritrea’s vast and struggling history has led to a
fascinating fusion of cultures. Asmara is full of wonderful vintage Italian
cafes and pizza parlours, and art deco Italian architecture, while Massawa on
the coast represents Eritrea’s Islamic influence and contains several works of
early Islamic architecture, although many of the historical buildings are
derelict and in need of repair.
St. Joseph’s Cathedral in Asmara was built during the Italian occupation of
Eritrea in the 1920’s. Its 57m tall Gothic bell tower is visible from everywhere
in
the city. Photo: Alec Robinson/Centric Energy
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