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Petrobras Deepwater Discovery Success

With its roots in exploration 55 years ago, Petrobras has matured into a world renowned integrated oil company without losing its explorer focus, leading the world in deepwater expertise.

By Graham Chandler

Petrobras is a perfect fit for exploration and production geophysicist Julio Lyrio, who joined the Brazilian company in 1987, "What makes Petrobras different from many other companies in the industry is the fact that it was born as an exploration enterprise," says Lyrio. "Fortunately this focus on exploration has not changed." To this day the company's main objective has been to discover where the oil is in Brazil. "The recent pre-salt discoveries are a validation of this dedication," he says.

Petrobras has a strong world presence in the oil and gas industry: it can boast the largest market value in Latin America, with nearly 70,000 employees operating in 27 countries; and two and half million barrels equivalent per day of production.

Significantly, it's a technological leader, recognized especially in the highly challenging deepwater exploration and production environments. "Challenge is our energy," quotes the company's website.

The pre-salt discoveries Lyrio refers to are recently-announced findings from those cutting-edge research techniques: in the Santos Basin 300 kilometres off the southeastern coast of the country and 7,000 metres below the South Atlantic Ocean surface. Potential is up to 33 billion barrels or more—some of the world's largest ever—of light sweet crude oil. Just finding them was a challenge. Beneath two kilometres of ocean water lies a post-salt layer (so-called because it was laid down later than the salt layer) half a kilometre thick, then another two kilometres of salt before reaching the pre-salt layer which contains the oil deposit.

That it was a challenge to find is an understatement. That post-salt layer is made up of high velocity rocks that can make it almost impossible to seismically image formations below them, because seismic waves in the salt have such a different velocity than the rocks above. And this is where integration of gravity and magnetics with seismic data were used to advantage.

Lyrio has learned the value of extensive integration of exploratory tools to reduce risk and enhance successes. "Gravity and magnetics have contributed effectively as tools to support interpretation that can produce quick results with low cost and reduced environmental impact," he says.

With the world of oil and gas exploration needing increasing sophistication as the easier deposits have been largely found and exploited, the importance of new and complex methods becomes paramount.

"The exploitation of hydrocarbons presents a growing demand in terms of technological innovations, particularly the software," says Lyrio. "In the field of geophysics, technological solutions that integrate different geophysical methods in exploration have become increasingly important." More and more today, gravity and magnetics are often shot well before bringing in the seismic equipment.

And the techniques are no longer restricted primarily to exploration of virgin territory either. Today, gravity and magnetic methods are being used in Brazil for re-evaluation of mature fields to extend production. Lyrio says Petrobras is using new and advanced gravimetric and magnetic interpretation in regions where environmental issues hamper the use of other geophysical methods such as seismic.

"In earlier times it was believed that the role of potential methods was limited to the initial stages of exploration," he says, such as delineation of basins and major geological structures. "With with the development of interpretation techniques, the availability of specialized software, new techniques for data acquisition, and development of measuring instruments, potential methods have expanded the exploratory process." He says Petrobras uses these potential methods where other methods present difficulties. Potential methods help the interpreters in mapping intra-sedimentary structures such as salt and volcanic spills, for example.

Lyrio describes a case where gravity data became a decisive factor in validating seismic. "During the interpretation of seismic data in a determined area, an important geological structure was defined," he explains. "But with the conversion of [seismic] data in time for depth, the mapped structure suffered significant modifications in terms of direction, and the interpreters were uncertain whether the new direction of the structure was real or only an artifact." He says once the gravity data were incorporated, the new structure was readily validated.

Choosing the right software for situations like this is critical in smoothing and speeding the interpretation process. "Petrobras uses the most advanced software in the market for potential fields," says Lyrio.  About 80 percent of the company's gravity and magnetic projects use the Geosoft platform for interpretation, preparation of maps and grids, and assembly of the database.

"The great advantage of using the Geosoft platform is the fact that it provides the ability for tight integration, from the database through to the preparation of the maps," says Lyrio.  "This has eliminated the need for multiple software and the constant migration of information from one program to another." The variety of software platforms with which Geosoft interacts makes it easy to exchange information between other exploration systems used by the company.
Another advantage that Lyrio likes: the software runs on a PC. "That's a benefit over other programs that require specific hardware," he says. Finally, he says it's very user friendly which makes the platform attractive to new users.

"The variety of tools available for processing and interpreting our gravity and magnetic data, and ease of application, allows us to achieve project completion in a short period of time," he says.

Petrobras' solution also includes company-developed software. "We have developed our own technology," he says, "mainly where the specialized functionality we require isn't commercially available."

Lyrio sees continued growth in the use of potential methods in geophysics well into the future, with a continuing resurgence in their application to hydrocarbon exploration. The reason he says lies in the increasingly complex geological problems being faced and the improved equipment available for dealing with them. He sees one of the largest changes on the horizon to be a change in scale—potential methods will no longer be mainly confined to the broader picture of major features, but will become a viable option for acquiring detail in more specific situations. "A consequence of this will be a bigger demand for technology to deal with integration of exploration methods," he says, "since the goals will be ever smaller and more difficult to interpret."