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marine engineering

Simulations on the screen and in the bay waters

Tanks from USP Coppe-UFRJ to help Petrobras explore for oil in ultradeep waters

eduardo cesarThree-dimensional image at The Poly-USP: special glasses to see the phenomena under studyeduardo cesar

Two test tanks, one virtual and the other physical, will strengthen Brazil’s position as technological leader in the oil exploration on the high seas. At the end of February, the Polytechnic School (Poly) of the University of São Paulo (USP) inaugurated a sophisticated laboratory called the Numerical Test Tank (TPN in the Portuguese acronym), which will make exploration more feasible in underwater wells located at depths of over 2,000 meters – at the moment, the Roncador field, in the Campos basin, in Rio de Janeiro, 1,800 meters from the water level, is the deepest one to be operated by Petrobras.

And, at the Federal University of Rio de Janeiro (UFRJ), researchers from the Coordination of the Post-Graduate and Research Programs in Engineering (Coppe) are putting the finishing touches to an oceanic tank that looks more like an artificial sea, with 22 million liters of water, which is forecast to be ready in June. Installed on the banks of Guanabara bay, on UFRJ’s campus, the oceanic tank covers 1,500 square metes, is 40 meters long and 30 wide, and an average depth of 15 meters, going to a maximum of 25 meters.

It surpasses tanks of the same kind existing in the United States, with 5.8 meters, in Holland, with 10,5 meters, and in Norway, with 10 meters in depth. The two projects were financed with funds from the Sectorial Fund for Petroleum and Natural Gas (CTPetro), of the Ministry of Science and Technology (MCT). Acquiring know-how for the exploration of petroleum and gas at great depths is of decisive importance for Brazil, since 75% of Petrobras’s reserves, estimated at 9.8 billion barrels, are found in deep (400 to 1,000 meters) or ultradeep (over 1,000 meters) waters.

Virtual tests
“The TPN will carry out the simulation of the behavior of maritime oil platforms on the high seas, allowing Petrobras to advance more safely in ultradeep waters”, says Kazuo Nishimoto, the Poly’s Professor of Naval and Oceanic Engineering and the coordinator of the recently inaugurated laboratory. Engineer André Paiva Leite, a technical consultant at Petrobras’s Exploration and Production Department, confirms the importance of the TPN: “The reliability of our floating systems will become much greater with the tests to be carried out in the new virtual test tank”.

The TPN is actually a computer system made up of a group of 60 computers operating in parallel. By the end of the year, another 60 PCs will be incorporated into the network, which has the capacity of taking up to 300 machines. “We will be expanding capacity as demand justifies such an investment”, says Nishimoto. The advantage of the group over isolated computers is that it produces much morecomplex calculationsin a short time. “Simulations that would take days to be carried out on an isolated workstation are concluded in a few minutes on the network”, the researcher explains.

Three-dimensional image
Besides the computers, the laboratory will also have a virtual reality room, which will use Silicon Graphics animation technology. This room will be used for projecting a three-dimensional image of the numerical simulation carried out by the computers. “We decided to incorporate into the TPN project a stereographic room with 3-D graphic computing resources, so we can visualize all the phenomena studied in the most realistic way possible”, says Nishimoto. These resources will make it possible for each test’s numerical analysis to be followed simultaneously by a visual analysis, facilitating understanding and helping the checking of the results.

The simulations of hydrodynamic and structural models carried out on the TPN will result in information on the behavior of semi-submersible platforms and anchored tank ships, known as FPSOs, which stands for Floating, Production, Storage and Offloading -, structures responsible for oil exploration on the high seas. The tests will also show the behavior of the anchorage cables that tether the platform or the ship to the bottom of the sea, and the risers, the tubes that take the oil from the well to the surface platform. All these elements are continuously subject to environmental factors, such as the action of the winds, waves and currents, which may cause damage and destabilize the platform or the ship, jeopardizing production. Knowing how to keep them as stable as possible is a decisive factor for successful exploration.

The Numerical Test Tank project had the participation of four research institutions, besides USP: the Institute of Technological Research of the State of São Paulo (IPT), Coppe, the Computer Graphics Technology Group (Tecgraf), from the Pontifical Catholic University (PUC) of Rio de Janeiro, and the Petrobras Research Center (Cenpes). The total investment in the project, which was part of CT-Petro first call for tenders at the end of 2000, amounted to almost R$ 3 million. Of this total, R$ 2,56 million was handed out by the Financier of Studies and Projects (Finep), a body that performs the role of Executive Secretariat for the Sectorial Funds of the MCT, and the remaining R$ 400,000 were for Petrobras’s account. The funds started to be injected in January last year, and the laboratory was set up in just one year.

According to Nishimoto, the TPN will provide the designers and engineers involved in projects for the construction of floating structures with valuable data. “We will be simulating mainly the basic parameters, like the movement and the acceleration of the platform and the tensions in the mooring ropes and the tubes.”

Reduced scale
The TPN supplements and extends the applications of the physical test tanks, which carry out tests using small scale models. In its turn, the TPN depends on the results obtained in the physical test tanks to validate and to adjust the numerical models used in the virtual model. The physical tanks are efficient, but they suffer from limitations in the simulations in ultradeep waters, because of the scale effect. Limitations that may be mitigated with integration with the tests carried out in the TPN. Today, the maximum depth possible for carrying out simulations is 1,000 meters. When Coppe’s tank is ready, operations at depths of up to 2,500 meters. To extrapolate these limits, complementary studies based on tests in the virtual tanks represent an effective contribution.

One advantage of the TPN is the cost of its tests, far lower than those carried out in the physical test tank. The savings in costs is also valid in the physical tank – its tests are indispensable in pioneering projects and for original and innovative concepts – mentioned the researchers from Coppe. The daily fee for using the oceanic tank does not come to US$ 15,000, while the tanks located abroad charge amounts that exceed US$ 20,000. According to Coppe, Petrobras spends as much as US$ 400,000 for 15 days of testing outside Brazil. Equipped to produce waves, winds and currents, the oceanic tank, with a maximum depth of 25 meters, will make it possible to test models of structures and equipment for activities in the production of oil and offshore gas (on the high seas), at great depths, research in the area of naval engineering, besides studies linked to the new oceanic structures and underwater operations.

“The testing of models under the conditions that we will have in the oceanic tank are fundamental for foreseeing what is going to be found at sea in extracting petroleum. And the deeper the tank, the better the results”, says civil engineer Ricardo Franciss, of Cenpes’ Underwater Technology Management, at Petrobras. “In the tank, we can observe with greater efficiency, reliability and lower risk such factors as fatigue, collapse, vibration, variation in tension and vortex (swirls) in the riser lines for example, as well as testing equipment involved in maritime operations. We will get the behavior of everything that is afloat or submerged almost under the same conditions that we find, for example, in the Campos basins”, he adds.

According to the researchers, several types of equipment and structures connected with exploration for oil will be able to undergo testing in the tank: platforms, ships for the exploration and storage of oil, cable that tether the platforms to the bottom of the sea, and transmission lines, among other items. The tank has mechanisms to cause the formation of waves of up to half a meter, at intervals that can vary from 0,3 to 5 seconds. The waves are produced by 75 driving panels positioned at one of the edges of the tank. Each panel has an independent motor and can create undulations with different movements and directions of propagation.

Underwater currents
Then the winds that are going to lash this “artificial sea” will be programmed by fans that can be positioned at any point close to the surface of the water. This equipment can generate winds with a speed of up to 12 meters a second and preprogrammed direction and variation in time. The tank will have a moveable bottom, which can go up and down, adjusting the depth between 1,4 and 15 meters, depending on the kind of test carried out. Its construction, which cost R$ 13,6 million, was financed with funds from CT-Petro.

In the second stage, expected to be concluded in one year, the underwater current system will be set up. Pumps will pour water into the tank from submerged galleries installed on one of the sides of the work, forming the currents. The water will then leave the tank through openings positioned on the other side, traveling through pipes until coming back to be injected once again into the tank. It will be possible to generate currents of different intensities and depths. To install this system, the group is raising supplementary funds amountingto R$ 8,2 million. The Carlos Chagas Research Support Foundation of the State ofRio de Janeiro (Faperj) has already set aside R$ 1 million.

About 15 professionals, including researchers, technicians, divers and support personnel, will be working with the tank. Sensors connected to the small scale models of platforms, ships, cables or underwater robots will record the responses of the equipment tested. A video system will record images in and out of the water. Through scuttles located below the waterline, it will also be possible to visually follow the tests. But this enterprise’s application go beyond testing models of equipment connected mainly with oil and gas exploration. For the professor of Oceanic Engineering, Segen Estefen, one of the coordinators of the oceanic tank project, underwater robotics will be another area to benefit from the new tank.

“A diver cannot today go beyond 400 meters in depth. Thus, robotized equipment will be increasingly necessary, as the exploration of the resources in the sea goes down to greater and greater depths”, he says. The environmental area will also have its share of advantages. Simulating waves, currents, and winds, it is possible to study the behavior of an oil slick on the water. “By analyzing a oil spill at sea, we can make the data available for use in the action to fight the problem”, says Carlos Levi, a professor of Oceanic Engineering and another coordinator of the tank project.

Important partnerships
The group from Coppe generated four doctorate theses, eight dissertations for master’s degrees, and 15 works of scientific initiation, with themes relating to the tank. All the stages of the project were accompanied by a technical committee made up of researchers from the IPT, from USP, from Coppe and from Petrobras. Partnerships, by the way, are strongly valued by the two groups. “We are going to exchange a lot of information from the data generated from the new test fields”, adds Levi. “These are tools of great importance for the area of tests connected with the oil exploration sector”, says Franciss, from Petrobras.

Strategic depths
A considerable share of Brazil’s oil reserves, amounting to 23%, is located in piece of the ocean that is between 1,000 and 2,000 meters in depth. Petrobras estimates that 50% of the reserves still to be discovered will be located in deep and ultradeep waters. “Technologies and innovations today are particularly focused on production in deep waters, because of the strategic importance that this area has acquired”, says Ricardo Franciss, of Petrobras’s Cenpes.

The company is leading the race for the exploration of oil and gas in deep waters. In the Roncador field, discovered in 1996 and located in the Campos basin, off the north coast of Rio de Janeiro, oil is extracted at a depth of over 1,800 meters, a world record for sea exploration. In the Santos and Espírito Santo basins wells at great depths were also discovered. Abroad, the pace of discoveries is slower. “With the exception of one well in the Gulf of Mexico, explored by Shell and located at 1,800 meters, the wells abroad do not go beyond 1,200 meters in depth”, Franciss reveals.

The company’s deep water production has been increasing significantly. In 1987, oil and gas extracted from wells located at great depths accounted for only 1,7% of the company’s total production. In 2000, this percentage rose to 55%. Petrobras has the target of attaining in 2005 the range of production of 1.850,000 barrels of oil per day. About 75% of this production will be taken out of the wells located in deep and ultradeep levels of water.

Since the mid-Eighties, Petrobras has been carrying out research to make it feasible to extract petroleum at greater depths. The Program for Technological Qualification in Deep Waters (Procap) was created in 1986 to encourage this activity. The program is in its third edition, Procap-3000, which, amongst other targets, intend to make new discoveries feasible in waters of up to 3,000 meters in depth.

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