Petrobras Magazine

Having discovered the oil-bearing province known as the pre-salt province, which extends for 800 kilometers along the Brazilian coastline, from the state of Espirito Santo to Santa Caterina and including the sedimentary basins of Espirito Santo, Campos, and Santos, Petrobras is facing important challenges. These include analyzing the multiple specifications of this new exploratory frontier, working to develop technological solutions to produce oil and gas in the location, and carrying out the necessary tests to choose the best alternatives, since there are presently no models to be followed.

Logistical challenges

Regarding the new province, there are many innovations. The high seas support logistics, that is the transportation of materials, equipment, and personnel and the installation of anchoring and well operation systems, will have to be specific to the project. After all, in the case of the Tupi accumulation, and others in the province, the distance from the Brazilian coast is considerable: 300 km.

In order to reach the oil reservoirs, more obstacles must be overcome. “It will be necessary to pass through a 2,000m water depth, a 1,000m layer of sediments and another 2,000m.of salt. This achieved, the recoverable oil and gas will be found in reservoirs needing greater drill penetration time than is required to penetrate the Campos Basin sandstone, for example, and, in the case of Tupi, at a distance of5,000 to 7,000m below sea level,” informs José Formigli, executive manager of Pre-Salt Exploration.

Geological Challenges

The type of rock present in the reservoirs has no precedent in Petrobras activities. “Instead of turbidites, characteristic of the large accumulations in the post-salt layer and long known to the company, we are finding microbial carbonate, also known as microbialites, formations of a heterogeneous character practically without parameters in world history and the behavior of which in terms of oil recovery is still unknown to us. Therefore we cannot replicate models similar to those already used in other basins,” explains Formigli.

Exploration Challenges

In the area of exploration, more challenges arise. When blocks situated in pre-salt were acquired by Petrobras and its partners in the Santos Basin, for example, blocks BMS- 8, 9, 10, and 11, as it was a practically unknown area of around 20.000 km², the company had to contract the largest 3D seismic marine survey carried out in the world to date. The seismic database obtained, of excellent quality, was fundamental to understand the geological context of the deepest sections of the basin and to interpret and map of the principal geological horizons of the blocks. These studies culminated in the proposal of more reliable exploratory locations, which led to the discovery of hydrocarbons in the pre-salt province of the Santos Basin, and are being used for a better understanding of the type of reservoirs in other stretches of the province and for predicting the next exploratory locations.

Environmental Challenges

The high degree of carbon dioxide extracted together with oil, more than 20% in the case of some reservoirs, is another problem receiving the special attention of Petrobras. Formigli explains why. “When CO2 combines with water, it forms a highly corrosive carbonic acid which requires the use of special steel alloys to avoid the corrosion in the well casing, in underwater production equipment, like Wet Christmas Trees, and in components of the processing plant on the production platform. In Tupi, for example, the proportion of natural gas is 220m³ for each cubic meter of oil, which is almost double the proportion found in the Campos Basin turbidites. The CO2 contained in this natural gas requires an ecological destination so that it does not escape into the atmosphere thereby contributing to an increase in the greenhouse gas effect. For this reason, the CO2 is reinjected into the wells, which brings the further advantage of reducing the viscosity of the remaining oil, making possible a greater potential recovery rate and, for this reason, ensuring a more lucrative operation for the company,” explains Formigli.

The formation of hydrates, substances resulting from the contact between gas and water, at low temperatures, which could result in the blocking of pipelines, must also be avoided. Strategies for avoidance will include conserving oil temperatures taken from the reservoirs and possibly increasing the oil temperature in the pipelines by electric heating or by injecting inhibitors.

Planning Challenges

Careful planning is essential in order to avoid frustrating all the efforts involved. In this area are included the acquisition of exploratory blocks backed by precise geological studies; the acquisition of seismic data, for the processing of which special logarithms were developed; and the meticulous evaluation and monitoring of data interpretation.

Five evaluation plans covering the extension of the wells and the volumes therein were requested of the National Oil, Natural Gas and Biofuels Agency (ANP) in order to guide the Petrobras strategies more accurately, and to avoid precipitous decisions. The plans will have a duration of five years and will precede any declaration of the commercial viability of the reserves.

Tests of long duration, such as the one which will begin in Tupi in March, 2009, and the following pilot phase when the forecast is to produce 100,000 barrels of oil equivalent and around 3.5 million cubic meters of natural gas per day starting in December, 2010, were also carefully planned. The objective is to ensure that when the fields come onstream, there will be absolute knowledge of the variables involved.

Technological Challenges

In order to confront the technological challenges, Petrobras created the Pre-Salt Technological Program (PROSAL), implemented by the company’s research and development center, CENPES. “Within the scope of this program, 23 projects with the objective of searching for the most effective solutions in the areas of Well Engineering and Reserve and Flow Assurance Engineering are in progress,” says the program coordinator, Cristiano Sombra.

The work is arduous. “To give you an idea, it is sufficient to say that the salt has a plastic nature. As it is drilled, its tensions could cause the well to close and the drilling column to become trapped. When the drilling phase is finished and the well is completed, a steel casing is lowered into the well and the existing space between the casing and the drilled rock is filled with special cement. The salt could damage the steel. To prevent this from occurring, we are researching resistant materials. However, we have to be careful to reach a balance, because, on the one hand, if the steel or the casing weighs too much, the drillship for placing this material may not succeed in doing the operation; on the other hand, as the oil drilling concession obtained could last for 27 years, and even be extended, the materials have to be durable,” explains Sombra.

Economic Challenges

Bearing in mind that work on the new exploratory frontier will require billions of dollars, Petrobras will adopt a pioneering approach in dealing with such a large scale undertaking. The company will have the cooperation of partners in developing the Pre-Salt province, although it will hold a majority stake in most of the blocks. Partners will include companies such as Amerada Hess, BG, Exxon, Partex, Petrogal-Galp, Repsol YPF Brasil, and Shell. The profitability of the undertaking is guaranteed for all. After all, as the executive manager of Petrobras Exploration, Mario Carminatti, states, “oil has been discovered in all the wells drilled, which means 100% success up to now in this new exploratory frontier. In addition, in Tupi alone, it is estimated that the recoverable volume of oil and natural gas is between five and eight billion barrels.”

Overcoming the challenges

Overcoming so many challenges pays off. After all, the oil discovered in the new province is light, 28° API, of excellent quality and high commercial value. In addition, the estimated volume of oil will compensate every effort made. Tupi, for example, has reserves ensuring that it will be considered as one of the largest discoveries in the world during the last seven years, which could transform Brazil into an oil exporting country. In this regard, each challenge arising is an additional stimulus to overcome the difficulties.