Potential In South America Tremendous

Where is the next big discovery?

West Africa may be grabbing the lion's share of international exploration interest, but here's a message for the industry:

The other side of the Atlantic Ocean looks pretty good, too.

In fact, Central America, South America and the Caribbean are poised to be hydrocarbon success stories. According to the U.S. Geological Survey's 2000 World Petroleum Assessment, the region ranks third in the world for undiscovered oil and gas resources, behind the Middle East and the former Soviet Union.

Specifically, the USGS estimates mean totals of 105 billion barrels of oil and 487 trillion cubic feet of gas of undiscovered resource in the region.

Not surprisingly, the greatest potential for giant oil and gas fields lies in the offshore basins along the Atlantic margin of eastern South America, from the Santos Basin in the south to the Guyana-Suriname Basin in the north.

The potential for giant fields is mainly offshore in water depths to 3,600 meters.

In addition, the basins of northern South America around Trinidad and Barbados as well as Venezuela are estimated to contain significant undiscovered natural gas resources, as are some of the Andean-related basins.

That all is according to Christopher Schenk, a USGS geologist who reported on the agency's findings at last fall’s AAPG International Conference and Exhibition in Barcelona. His paper was titled "Assessment of Undiscovered Oil and Gas Resources in Central America, South America and the Caribbean."

The USGS studied 23 basins in Central and South America and the Caribbean area. In each basin scientists geologically:

  • Defined total petroleum systems.
  • Defined assessment units within total petroleum systems.
  • Assessed the volumes of undiscovered conventional oil and gas in each assessment unit.

The USGS defined 28 total petroleum systems and 55 assessment units in the basins.

Schenk said that 83 percent, or 87 billion barrels, of undiscovered oil is estimated to be in the total petroleum systems in the Guyana-Suriname, Campos, Santos, Falklands Plateau, East Venezuela, Maracaibo, Llanos and the Putumayo-Oriente-Maranon basins, with two thirds of that total estimated to be offshore.

For undiscovered non-associated gas, an estimated 61 percent of the resource is in the total petroleum systems of seven assessed basins — six of which are predominately offshore: Foz do Amazonas, Espirito Santo, Santos, Pelotas, Santa Cruz-Tarija, the Tobago Trough and East Venezuela, which includes the Columbus Basin offshore Trinidad.

"The exploitation of these oil and gas resources in South America," Schenk said, "means that the emphasis on future exploration will move offshore to water depths approaching 4,000 meters."

Geologic Factors — and Results

Three major geologic events shaped the development of total petroleum systems and composite total petroleum systems in Central America, South America and the Caribbean. The resource assessment grouped total petroleum systems into these three categories.

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West Africa may be grabbing the lion's share of international exploration interest, but here's a message for the industry:

The other side of the Atlantic Ocean looks pretty good, too.

In fact, Central America, South America and the Caribbean are poised to be hydrocarbon success stories. According to the U.S. Geological Survey's 2000 World Petroleum Assessment, the region ranks third in the world for undiscovered oil and gas resources, behind the Middle East and the former Soviet Union.

Specifically, the USGS estimates mean totals of 105 billion barrels of oil and 487 trillion cubic feet of gas of undiscovered resource in the region.

Not surprisingly, the greatest potential for giant oil and gas fields lies in the offshore basins along the Atlantic margin of eastern South America, from the Santos Basin in the south to the Guyana-Suriname Basin in the north.

The potential for giant fields is mainly offshore in water depths to 3,600 meters.

In addition, the basins of northern South America around Trinidad and Barbados as well as Venezuela are estimated to contain significant undiscovered natural gas resources, as are some of the Andean-related basins.

That all is according to Christopher Schenk, a USGS geologist who reported on the agency's findings at last fall’s AAPG International Conference and Exhibition in Barcelona. His paper was titled "Assessment of Undiscovered Oil and Gas Resources in Central America, South America and the Caribbean."

The USGS studied 23 basins in Central and South America and the Caribbean area. In each basin scientists geologically:

  • Defined total petroleum systems.
  • Defined assessment units within total petroleum systems.
  • Assessed the volumes of undiscovered conventional oil and gas in each assessment unit.

The USGS defined 28 total petroleum systems and 55 assessment units in the basins.

Schenk said that 83 percent, or 87 billion barrels, of undiscovered oil is estimated to be in the total petroleum systems in the Guyana-Suriname, Campos, Santos, Falklands Plateau, East Venezuela, Maracaibo, Llanos and the Putumayo-Oriente-Maranon basins, with two thirds of that total estimated to be offshore.

For undiscovered non-associated gas, an estimated 61 percent of the resource is in the total petroleum systems of seven assessed basins — six of which are predominately offshore: Foz do Amazonas, Espirito Santo, Santos, Pelotas, Santa Cruz-Tarija, the Tobago Trough and East Venezuela, which includes the Columbus Basin offshore Trinidad.

"The exploitation of these oil and gas resources in South America," Schenk said, "means that the emphasis on future exploration will move offshore to water depths approaching 4,000 meters."

Geologic Factors — and Results

Three major geologic events shaped the development of total petroleum systems and composite total petroleum systems in Central America, South America and the Caribbean. The resource assessment grouped total petroleum systems into these three categories.

These are:

The development of the Andean mountain chain.

The tectonic development of the Andean chain in the Tertiary led to the formation of a fold and thrust belt and a segmented foreland basin that extends the length of the continent.

Pre-Andean, passive-margin marine source rocks in many of the assessed provinces reached generative maturity for oil or gas because of tectonic loading or burial by thick Tertiary synorogenic clastic sequences.

"We assessed several provinces with total petroleum systems that evolved largely because of Andean tectonism, including systems in the Magallanes, San Jorge, Neuquen, Santa Cruz-Tarija, Putumayo-Oriente-Maranon, Talara, Progreso, Middle Magdalena and Llanos basins," Schenk said.

Many of the Andean basins have been heavily explored, and the potential for large oil discoveries is minor.

"Basins such as the Putamayo-Oriente-Maranon have been producing for decades, and we did not give those a great deal of additional undiscovered oil resources," Schenk said. "However, there were some Andean basins with significant remaining natural gas potential."

An example: In the Santa Cruz Basin along big, re-activated Paleozoic structures.

"The Bolivian government has recognized this resource and is starting to exploit it," Schenk said. "The pipeline into Brazil is from this region."

Colombia's Llanos Basin is still prospective, according to the USGS.

"The basin has been heavily explored, but it is structurally very complicated, so there likely are remaining undiscovered oil resources," he said. "Of course, the future won’t be as great as the past, but there is still potential.

"The figures for our study do not include potential for additional reserves in existing fields, and this could be considerable for the Llanos Basin," he added. "It will likely be much like Prudhoe Bay, where the first reserve estimates were nine billion barrels of oil and today the total is up to 13 billion barrels."

To the north, the evolution of the Caribbean plate.

The Caribbean Plate's oblique collision with South America's passive northern margin in the Tertiary formed a series of foreland basins across Venezuela in which the deposition of thick synorogenic clastics led to the maturation of the Upper Cretaceous La Luna Formation and its stratigraphic equivalents, according to the USGS.

While the Maracaibo and East Venezuela basins are extensively explored and the La Luna total petroleum system is known in some detail, the total petroleum system in other assessed Caribbean basins — the Carupano Basin and the Tobago Trough, for example — are far less understood, according to Schenk.

The Maracaibo has been producing for 100 years from coastal fields, but he said there may be some potential down deep in the deeper parts of the basins.

"Again, field growth will be a big factor in these basins, and that figure is not included in our estimates," Schenk said. "We defined the East Venezuela Basin to include the big gas basins off Trinidad, so the bulk of the mean 93 trillion cubic feet of estimated undiscovered gas resource is from that emerging region."

Several significant gas discoveries have been made in the Carupano, a small basin northwest of Tobago in the Tobago Trough. The basin is not well known, and Schenk said there is about as much remaining undiscovered potential as the total found to date.

"That is a nice little gas basin that surrounds the countries of Tobago and Grenada in international waters," he said. "The major problem in this part of the world is ownership issues. The Trinidad-Venezuela border, the Trinidad-Barbados border and the Guyana-Suriname border are all under dispute. That will be a real hurdle for companies interested in the region."

Still, there are resources worth searching for in the area, such as the Lesser Antilles Deformed Belt offshore Barbados.

"I felt there was potential to the west offshore Barbados, where there are some big structures and known source rocks," he said. "Conoco recently drilled a well offshore southwest Barbados in about 5,000 feet of water, so it will be interesting to see the results of that effort when they are released."

The opening of the Atlantic — especially the south Atlantic region, where the lion's share of undiscovered South America potential is buried.

The Atlantic opening and subsequent rifting in the Jurassic and Lower Cretaceous led to the formation of a series of rift-drift basins along the length of the continent's eastern margin.

Many of the source rocks in these basins are genetically related to synrift and transitional-marine sediments, and clastic wedges of the drift phase are interpreted to have sufficient overburden to mature several of the source rocks, the USGS report indicated.

The Guyana-Suriname Basin, the region's northernmost province, is virtually untouched.

"I spent a week (there) with the state oil company looking at all their data," he said, "and the basin looks very prospective."

There is:

  • Production onshore that proves there is a working oil system.
  • Likely a Cretaceous source rock offshore, which coupled with the turbidite reservoirs make a good package.
  • Good evidence that the onshore oil fields are sourced from down dip in the offshore area.

The USGS estimates a mean 15.2 billion barrels of oil undiscovered resource for the basin.

Other Potential

Unlike the Guyana-Suriname, the Foz do Amazonas Basin has very little potential for oil, according to the USGS — but mean undiscovered natural gas estimates totaled a whopping 30 trillion cubic feet of gas.

The basin includes the total petroleum system associated with 10 kilometers of deltaic and slope sediments deposited off the Amazon shelf since the Miocene. Schenk said several deltas around the world have produced considerable gas from very similar settings.

There is one gas field in the basin. Plus, bottom simulating reflectors indicate thick gas hydrates, which suggest there may be thermogenic gas generation at depth in the total petroleum system.

The Sergipe-Alagoas and Espirito Santo are small Brazilians basins with both onshore and offshore components. However, a great deal of oil has already been produced from these basins, so the remaining undiscovered resource is not large compared to other basins in Brazil, Schenk said.

The Campos Basin, one of the world's most studied petroleum systems, has three assessment units: the Late Cretaceous-Tertiary turbidities that account for giant fields like Roncador, Marlim and Albacora; the Cretaceous Carbonates that contains the first offshore field discovered in the basin; and the salt dome province Tertiary sandstones, which is hypothetical and defined to include petroleum trapped in salt structures in ultra-deep waters of the Campos Basin.

The USGS estimated a mean average of more than 16 billion barrels of oil for the basin and over 19 trillion cubic feet of primarily associated gas.

The Santos Basin is deeper and hotter than the Campos and perhaps the most prospective under explored basin in South America.

While there is a good deal of uncertainty in the USGS numbers, mean undiscovered oil resources for the Santos are about 23 billion barrels of oil and the mean natural gas estimate is over 80 trillion cubic feet.

Petrobras is now zeroing in on this basin and beginning to exploit the natural gas potential, Schenk said.

The Pelotas Basin is related to the thick wedge of clastic sediments deposited in the Rio Grande cone and other centers of clastic deposition along the Pelotas shelf edge.

The composite total petroleum system in the basin is defined based on the presence of thick gas hydrates in the upper part of the sedimentary section — a possible indication that thermogenic gas is being generated at depth in the clastic wedge, according to the USGS.

The Falklands Plateau and the Malvinas Basin have both been studied, and large structures have been mapped in the Falklands Plateau, but there is uncertainty over the presence of an adequate source rock.

"There is a lot of questions about how the fluid system would work here — whether enough source rock has been heated up and whether it would have generated enough fluid to fill the prospects," Schenk said. "There have been several wells drilled and they were disappointing. Today it looks like there are good structures with nothing in them.

"There may still be some potential," he added, "but somebody is going to have to demonstrate that there is an adequate source rock."

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