By KATHY SHIRLEY
EXPLORER Correspondent

Cold War Maps Prove Boon for Explorers

Big East Africa Structures Enticing

Photos courtesy of Robert Bertagne

A home-away-from-home: The "Echo Lima" Cessna 401 air taxi, at the landing strip in the project's seismic camp.

Seismic Data

Barcelona Posters Examine

East Africa Margin Potential

The poster "New Petroleum Exploration Concepts Related to the Davie Fracture Zone, Offshore East Africa," by D.C. Rusk and Robert Bertagne, will be presented at the AAPG International Conference and Exhibition, set Sept. 21-24 in Barcelona, Spain.

The poster is one of nine to be presented in a Tuesday afternoon session, co-chaired by Bill St. John and G. Tari, on "Exploration Frontiers: East Africa, One of the Last Unexplored Passive Margins."

Other posters in the session include:

• "Frontier Exploration in East Africa - Beyond Seismic."
• "The Evolution of the East Africa Passive Margin and Petroleum Systems."
• "Tectonics of the Western Indian Ocean."
• "Salt Tectonics and Basement Structure in the Majunga Basin, Offshore Madagascar, as Revealed by New Shipborne Gravity and Magnetic Data."
• "Hydrocarbon Potential of Western Madagascar."
• "East Africa And Western India: Passive Margins from the Evolution of a Complex Ocean."
• "The South African East Coast: Evidence for an Active Petroleum System within the Tugela Fan, Durban Basin."
• "Basement Controls on Structure and Sedimentation in the Offshore Zambezi Delta Region."

The hosts for the AAPG meeting is the Institut Cartográfic de Catalunya (DPTOP).

The meeting will offer more than 500 papers and posters around the theme "Crossroads of Geology, Energy and Cultures."

The pre-registration deadline is Aug. 15, and attendees can register online.

East Africa Offshore Study Conducted in Three Phases

The offshore East Africa study by Bertagne and Rusk, in partnership with TGS-NOPEC Geophysical Co., was conducted in three phases:

The first phase included a comprehensive evaluation of the petroleum systems, including play characteristics with emphasis on structural trends, leads and prospects.

The second phase addressed the reprocessing of selected seismic lines to enhance the quality of the data and gain additional knowledge of relevant aspects of the stratigraphy and structure.

This was independent of the initial phase and was jointly conducted by TGS-NOPEC and Rusk, Bertagne & Associates.

The final phase consisted of four sub-phases to map the major structural trends delineated in the initial part of the work.

A total of 33,000 kilometers of seismic control will be available for this phase, and additional selective 2-D reconnaissance seismic already has been acquired, processed and interpreted.

The completion of phase three is contingent on industry demand and ratification of boundary agreements between the neighboring countries and approval of the seismic acquisition programs by the host governments.

Checking the data, looking for clues and signs of that famous black gold.

These idyllic East Africa settings, once a hot seat for Cold War activities, are now potential
hot spots for exploration: Saint Mary Island, east of Madagascar, and the Catfish LCT.

It sounds unlikely, but it's true: Thanks in part to the deadly serious cat-and-mouse Cold War military games played a few decades ago, there's a renewed scientific and industry interest in offshore East Africa.

Something good coming out of the Cold War?

Who knew?

Looking down on potential success: Mozambique Channel islands.

Offshore East Africa, unlike the prolific success stories involving offshore West Africa, has had only sporadic attention -- and none in the deepwater regions. But a recent geologic and geophysical study of the area, based on data gathered as a cover for Cold War military maneuverings, shows promise for the region's future.

"When we made the decision to study the Mozambique Channel region we began researching existing data, and after some digging (we) realized that what had been termed 'scientific surveys' were actually efforts to map the sea floor for submarine movements," said Bob Bertagne, a principal with Rusk, Bertagne & Associates, a Houston-based geologic consulting firm.

"During the Cold War the Soviet Union maintained a number of submarines in the area to sink the oil tankers and cut supplies to Europe and the Eastern United States in the event of war," Bertagne said. "However, to safely park the submarines they had to have some information about the makeup of the seafloor. So the Russians conducted a series of 'geophysical' surveys as a front to map the sea floor."

This information is now available, and western scientists have been in contact with the U.S.S.R. Academy of Sciences to assist in publishing the maps, which are now used for scientific purposes.

Of course, the West powers were forced to monitor the actions of the Russians and, in turn, ran their own "surveys," including bathymetric, magnetic, gravimetric and seismic reconnaissance.

France, with the assistance of the U.S. Navy and intelligence organizations, was entrusted with much of this work since the country had a military presence in the area.

'Size Does Matter'

So what does all this background mean for oil and gas exploration today?

Plenty, according to Bertagne.

Based on the three-year study of 1.3 million square kilometers, or one-third of offshore East Africa, the scientists reported that this large frontier area, which is one and a half times the size of the North Sea, comprises nine sedimentary basins with only limited exploration on the shelf areas.

The basins display:

• Varied structural styles.
• A thick sedimentary section of over 10 kilometers.
• The presence of evaporites.
• Signs of being mostly oil-prone.

Bertagne said the study indicates multi-petroleum systems combined with mega-anticlinal structures. Several prospects at average depths of about 2,000 meters and in technologically manageable water depths of 1,300 to 1,600 meters could rapidly establish the area as a major hydrocarbon province.

"Size does matter, and this region could potentially be another North Sea or even another Middle East," he said. "These are some of the biggest structures I have ever seen in my career."

How big? Bertagne's estimates are of several mega structures in the area, and conservative estimates would be in the billion barrels range for each.

"These structures exhibit Middle East reserves potential," he said.

In addition, the period of expulsion and migration of hydrocarbons is synchronous with the growth of the anticlinal structures.

The study also notes that sea bottom samples and core holes drilled during reconnaissance work by the Russians and French indicate that the Davie Fracture Zone -- a large geologic feature in the region -- is not of volcanic origin, but is a more recent wrench fault zone similar to the San Andreas Fault oil province in California.

There is ample evidence of hydrocarbons in the region:

• There are large fossil oil fields in Madagascar, including the Bemolanga tar sands with 21 billion barrels of reserves and Tsimiroro with eight billion barrels of reserves.
• In Mozambique the Pande-Temane gas field, now under development, is expected to contain recoverable reserves of approximately four trillion cubic feet of gas.

The political outlook for the area seems positive as well:

• The offshore region has large amounts of open acreage.
• It is surrounded by welcoming governments with attractive production sharing terms.
• It is in close proximity to the traditional tanker route to Europe and the Far East. Excellent marine facilities at the ex-French naval base, Diego Suarez, in northern Madagascar could provide a supply base and manufacturing and repair station.

Exotic exploration: The Isalo massif northeast of Toliara (Tulear), Madagascar (left), and a closer view of the karst platform.

Frontier Play 

This vast multi-basin province is basically a frontier, with only a handful of exploration wells drilled offshore for a ratio of one well per 56,000 square kilometers, according to Bertagne.

However, the region is known to have hydrocarbon potential.

A Baobab tree, near Morondava.

In addition to the Pande and Temane fields in southern Mozambique and Madagascar's Bemolanga and Tsimiroro trends, there are two gas discoveries with estimated reserves exceeding two trillion cubic feet of gas offshore southern Tanzania.

Bertagne said the source for the tar and oil deposits and the reservoirs involved are expected to be present in the offshore.

The water depths have stalled offshore exploration in the past. Much of the activity in the region was in the 1950s through 1970s when deepwater drilling was not feasible. Twelve wells were drilled between 1955 and 1960, and the next drilling phase did not occur until 1971 when Conoco and Chevron drilled three wells each by 1975.

From 1985 to 1988 Amoco drilled four wells along the coast in the Morondava Basin, and in 1988 Petro-Canada made a gas discovery with its West Manambolo 1 well, according to Rusk and Bertagne.

In the Majunga Basin, AGIP drilled two offshore wells in 1971. Southern Mozambique enjoyed a fairly continuous exploration effort by Gulf and Gulf-Amoco from 1953 to 1970, and this venture resulted in the Pande, Temane and Buzi gas discoveries onshore and added two offshore tests to the region's well control. Elf Aquitaine, Hunt and Sunray also drilled offshore wildcats in southern Mozambique during the early 1970s. Additional activity in the Rovuma Basin resulted in the AGIP Songo-Songo gas discovery, which is currently being developed, and the AGIP-Amoco Mnazi Bay 1 gas discovery.

The Smoking Gun 

When Bertagne and Rusk initially decided to study offshore East Africa there was a great deal of negative assumptions about the region's potential.

"Following the drilling activity in the 1970s, many oil companies saw three problems in the area," Bertagne said:

• It is a passive margin, much like the U.S. East Coast.
• As a result of a huge 1953 blowout in Mozambique that astronauts could see from space, many were convinced this was a gas prone region, which until recently was a major problem in international frontiers.
• Due to scientific work done by the French and others, many scientists felt the structures along the Davie Fracture Zone were volcanoes.

"Don Rusk and I had to think outside that conventional wisdom," he said. "This is a passive margin, but that did not deter us. A passive margin can contain oil just like other structures and petroleum systems.

"Based on our personal experience in the region we knew this was not solely a gas rich area -- there were oil prone source rocks and oil deposits," he continued. "And we determined to keep an open mind about whether these were volcanic structures until we could take a better look."

During the Cold War, people looked at these regions and saw strategic scenarios. Today, explorationists are seeing fascinating hydrocarbon potential.

After three years of study, they feel they have proven these are in fact not volcanoes.

"The 'volcanoes' that appeared on the sections recorded by the French were compressed horizontally five times," Bertagne said. "Thanks to computer technology we were able to stretch the section without changing the vertical scale to the horizontal scale of a typical seismic section. That exercise indicated these structures are actually anticlines."

Bertagne and Rusk also were able to obtain data from the French concerning 119 bottom samples and cores from the Davie Fracture Zone. At the time those samples were taken decades ago, the French were looking for volcanoes as part of the Cold War military maneuverings. However, the cores and samples showed the structures were not volcanic in nature. A paleontologist studied the cores and samples for the authors and determined they were actually Cretaceous, Eocene and Karoo sediments.

"That was the smoking gun for us that turned conventional wisdom about the region on its ear," Bertagne said.

"People may say as explorers we are dreamers, but throughout the history of the petroleum business it is persistence and dreamers that have lead to some of the major discoveries," he said, citing BP's experience on Iraq's Kirkuk Field as an example.

"The manager of the local BP office had gotten a Telex to abandon the wildcat, but the geologists on site were excited about the possibilities and knew they were stopping short of the objective," he said. "To give the explorers more time, the manager decided he could only act on written instructions, so until the official letter arrived they would continue drilling.

"By the time the letter reached the field office BP had discovered a super giant oil field.

"There are stories like that throughout the history of this industry," he said. "We may be proven right or wrong in the Mozambique Channel, but until we explore the region we will never know."