By KATHY SHIRLEY
Intriguing Geology Defines West Africa
Despite the political and sociological problems that
exist for West Africa exploration, the region's geology is making
the effort worthwhile -- as is the prospect of future giant discoveries.
Today, more than 70 years after Alfred Wegener first
proposed his theory of plate tectonics and the break up of a super
continent, geologists are uncovering the secrets of the mirror geologic
histories of Africa's West Coast and Brazil's offshore region --
both at the time of the separation and through subsequent developments.
Both coasts are yielding some of the world's greatest
deep water oil fields.
"As the split between the continental landmasses
developed from the Late Jurassic into the Early Cretaceous periods,
contemporaneous pre- and syn-rift deposits were laid down on both
sides of the South Atlantic," the Knight-Harbinson report reads
(see accompanying story, page 18). "Thus were produced two very
similar hydrocarbon provinces with regard to basin type, source
rocks and salt deposits.
"The salt deposits were laid down in a region of
poorly circulating waters lying north of the volcanic rocks that
now constitute the Walvis Ridge in the eastern South Atlantic and
the Rio Grande Rise in the west," it continued. "The location of
these two volcanic ridges still effectively delineate the southern
margins of the hydrocarbon bearing Lower Congo and Santos/Campos
basins to the north."
Further rifting led to the opening of the South Atlantic
and the deposition of a series of post-Aptian clastic post-rift
sediments as the marginal shelves subsided, the report continues.
The salt deposits are of particular importance because
of the effect they have on the post-depositional sediments that
blanketed them as the ocean opened, and a massive basin-ward influx
of turbidites and other closely related Tertiary clastic deposits
These turbidite fan deposits -- particularly those
of the Oligocene and Miocene age -- now form the bulk of the reservoir
rocks in the Congo Basin's deep water fields. They lie off the continental
shelf, below the continental slope, and finds have been made in
water depths of 300 to 1,893 meters.
"The recognition of the importance of these deep
sea fan deposits over the shallow water progradational shelf deposits
. . . is one the most important discoveries to come out of deepwater
exploration," the report said.
Recent seismic surveys in the Angolan portion of
the Lower Congo Basin and in the Campos Basin show that post-depositional
salt movements have created various trap types in the overlying
The salt thickens toward the African shore, producing
different structures in the basin's upper margin extensional tectonic
environment, from those that occur in the area affected by compressional
tectonics (western and deeper parts of the basin).
-- KATHY SHIRLEY
The relatively small, relatively sparsely
populated countries along the West African coast are poised to become
major players in the world oil arena in the next five years.
Giant deep water discoveries found in the region
are beginning to come on line, and new deep water finds all along
the coast are as sure a bet as there is in this risky business.
In fact, many experts believe -- privately, but with
a passion -- that West Africa will likely emerge as the world leader
in offshore exploration and production activities in the coming
Of the world's 120 deep water field discoveries identified
for development in 2000-2005, West Africa accounts for 17 of those
finds -- just a fraction of the 75 found in North America, perhaps,
but in terms of reserves West Africa tops the Gulf of Mexico and
Brazil's Campos Basin.
The 17 fields, according to a report by Roger Knight
with London-based Infield Systems and Dominic Harbinson with Douglas-Westwood
in Canterbury, England, have combined reserves of over nine billion
barrels of oil equivalent and an average field size of 535 million
barrels of oil equivalent.
The only fields that come close to those numbers
are found in the deep water Campos Basin, which geologically is
a mirror image of West Africa.
"Liquids production of almost three million barrels
a day could be achieved by fields coming on stream in the region
over the period to 2005," according to the report.
Leading players are Angola and Nigeria, both with
1.2 million barrels a day of potential additions.
"Placing this in a global context," the report continues,
"over the next five years West Africa could account for 21 percent
of global offshore liquids reserves brought on stream, second only
to the Europe/Mediterranean region."
The world's deep water fields identified for development
over the 2000-2005 period will have average production rates of
over 34,000 barrels a day of liquids, but West Africa's fields will
far exceed that average with approximately 93,000 barrels daily
-- over five times the average expected productivity of deep water
fields in the Gulf of Mexico identified for development during the
The 17 deepwater fields could boost regional liquids
production by almost 1.6 billion barrels a day, or about 40 percent
of the deep water additions to global liquids production.
TotalFinaElf is the dominant player in the fields
slated to come on line through 2005. The French operator holds over
a third of the reserve base set for development in that period.
Four other majors, namely ExxonMobil, Texaco, Chevron
and Shell, also have substantial positions. Their combined holdings
amount to almost 50 percent of deep water reserves identified for
Since 1997, Infield Systems and Douglas-Westwood
estimates indicate that West African offshore field development
expenditures have been reasonably steady, averaging $2.4 billion
But that will all change in the next five years.
The companies forecast field development expenditures
to increase to $3.8 billion this year and grow to potentially $10.4
billion by 2005.
The bulk of these expenditures -- 78 percent -- will
be offshore Angola and Nigeria.
The major components in these capital outlays are
floating production systems, which, when added to costs of shallow
water platforms, will result in surface or platform-based facilities
accounting for 70 percent of the expenditures.
The report forecasts installation of 33 floating
production systems in the next five years -- some being extremely
costly. Elf's Girasol unit offshore Angola, for example, is expected
to exceed $900 million.
Large deep water fields also will require considerable
numbers of subsea well completions -- 297 are likely to be installed
by 2005, at costs that are estimated to exceed $4.8 billion.
When the associated templates, control lines and
systems are added that figure jumps to over $6.9 billion.
A Few Concerns
While the reserve figures for West Africa's deep water
province are impressive and headline-grabbing, some serious issues
remain to be addressed.
Those, according to the report, include:
- Political and commercial corruption and instability.
- Unfamiliar and often inefficient commercial practices.
- A dearth of adequate local service and supply facilities.
- Occasionally hostile local communities.
In Nigeria's Niger Delta, for example, popular agitation
over the perceived inequities in the distribution of oil wealth
has led to violence that may have cost Nigeria up to $1 billion
in lost oil revenues in 1999, according to the report.
Deep water discoveries, of course, should be less
susceptible to local problems since they are too far from the coast
to be easily disturbed.
Still, an issue companies must face is West African
governments' demands for greater levels of involvement in the decision-making
process toward field development.
Proving the Potential
The first giant deep water fields discovered offshore
West Africa were Shell's Bonga on Nigerian block OPL 212 and Elf's
Girassol in block 17 off Angola in the spring of 1996.
Since then, 44 fields have been discovered in water
depths of 500 meters or more, with the deepest discovery to date
being Elf's Andromede Marine field, found in early 2000 off the
Congo in 1,893 meters of water.
According to the report, ExxonMobil's Topacio satellite
off Equatorial Guinea in 579 meters of water is the only deep water
field on production in the offshore West African deep water region.
Topacio, which is part of the firm's Zafiro project,
came on line in 1997 and is currently flowing 6,000 barrels of oil
a day to the Zafiro Producer floating production system.
Triton's La Ceiba Field in 700 meters of water offshore
Equatorial Guinea's Rio Muni province was expected to come on-stream
by early 2001.
These two fields make the small nation of Equatorial
Guinea (population -- less than half a million) the current leader
in the region's coming deep water production.
By 2005 Nigeria, Angola and the Congo will join their
neighbor among the world's important oil and gas producing nations.