Prograding oceanic sequence may lead to more large reserves

FPSO II- Marlim South Field. (Photo by Petrobas/Eliana Fernandes).

• P-XIX- Marlim Field (Photo by Petrobras/Eliana Fernandes [38,471 bytes]
• Many Campos Basin blocks are reserved for Petrobas. Highlighted blocks are reserved by ANP for later licensing. In preparation for production increases Petrobras is drilling a total of 13 Campos wells in waters deeper than 275 meters. [88,511 bytes]

The Campos Offshore Basin is the largest producing area in Brazil and one of the most prolific of the Atlantic Margin type in the world. The basin lies off the coast of the state of Rio de Janeiro, in the southeastern part of Brazil.

With an area of 115,800 sq kilometers, the basin is limited by the Cabo Frio Arch to the south, which separates it from the Santos Basin, and the Vitoria High to the north, which separates it from the Espirito Santo Basin. In longitude, it stretches from onshore east into the South Atlantic to a water depth of 3,400 meters.

The high prospectivity of the basin may be explained by the timing of the hydrocarbon migration and the previous existence of structures. The Campos Basin is producing around 750,000 b/d of crude and 12 MMcm/d of gas. The total oil and gas reserves discovered are of 11 billion boe.

Development sequence

First discovered in 1974 and brought onstream in 1979, it was only in the mid-1980s that Petrobras started drilling exploratory wells in what in Campos was known as deepwater. For most oil plays around the world, deepwater is somewhere between 400 ft and 600 ft, Petrobras considers deepwater as anything beyond 400 meters. That move led to the discovery of a series of giant fields, the first one being Albacora, discovered in 1984. The others that followed were:

• 1987 - Marlim
• 1990 - Bijupera/Salema
• 1991 - Barracuda
• 1994 - Espadarte
• 1995 - Caratinga
• 1996 - Roncador.

All these fields are located in structural and stratigraphic trends. There is a strong possibility of successful discovery of other giant fields in these trends, as demonstrated by the recent discovery of the Roncador Field, a 2.4 billion boe deposit in the northern part of the Campos Basin.

With the changes in the oil scene here, Petrobras retains the areas where it is already producing. It requested an exploratory area of 66,463 sq km in Campos and was awarded 53,095 sq km - a 20% cut. Taking into consideration the whole of the Campos Basin, including areas not requested by Petrobras which automatically pass to the ANP, Petrobras now holds 44.7% of the Campos sedimentary basin and the remaining 55.3% are in the hands of the agency for offer in future rounds of bids.

Campos bids

This division leaves in the hands of ANP, two small blocks in shallow waters - BC-ANP-3A and BC-ANP-3B, and six others in deep waters - BC-ANP-700, BC-ANP-600, BC-ANP-500, BC-ANP-2, BC-ANP-100A and BC-ANP-100B. These blocks will be among the first to go up for bids.

Operators and financiers interested in this area can count not only on those eight blocks, but also another dozen or so that were granted to Petrobras for at least an exploratory period. These are where the Brazilian national oil company will likely take on partners, and in some cases has already done so.

These blocks include ultra-deep regions, going down to 3,000 meters, and present new challenges for development and production. Petrobras has field-proven capacity beyond the 2,000 meter water depth range. But, if a big field were discovered in even greater depths, the technology to bring it onstream would be available in the beginning of the next century.

Prograding sequence

Geological expectations for continuing discoveries in even deeper waters of the Campos basin are based on the fact that the largest volumes of oil accumulated in the Prograding Oceanic Sequence. In this prolific basin, this sequence is comprised of the Eocene, Oligocene, and the Miocene, the geologic times when the Upper Cretaceous sediments would have reached their maturation peak.

The deposition of deep and ultra-deepwater turbidite reservoirs gave rise to giant fields, like the Albacora Principal, Albacora Leste (East), Barracuda, Caratinga, Marlim Principal, Marlim Sul (South), and Marlim Leste (East) fields. Also important are the Upper Cretaceous turbidite reservoirs that belong to the Hemipelagic Oceanic Sequence such as those in the Roncador and Marimba fields.

It is quite possible that the exploration blocks located in ultra-deepwater, both those granted to Petrobras and those kept by the ANP, contain important turbidite reservoirs belonging to giant fields to be discovered.

Author

Umberto Caseli, a former Petrobras reservoir engineer with three decades of experience in Campos and other Brazilian basins, is now an associate of the consulting company Aexpro. He co-authored the recent Campos Deep Water Prospects Report.

New innovaions ready for depths beyond 6,000 ft

Petrobras continues its concentration on deepwater and maintains a slow but steady march into deeper water. The motion started 20 years ago, In a sense, the march is forced, because it is in ever greater depths that Petrobras is finding larger reserves.

To explore and produce from such great depths, and do so both safely and economically requires a constant input of technological innovations. Petrobras has been pursuing this objective for many years and lately has been investing close to 1% of its gross income in its research and development center, CENPES.

Although some of the technology comes from abroad, the homegrown methods along with adaptations and experimentation with the imported ones, have earned Petrobras the label of deepwater pioneer. Campos is often referred to as the "deepwater laboratory."

"In order to bring onstream the well in greatest water depths in the world, the MS-3 in South Marlim Field," Petrobras Director Carlos Agostini explained, "we had to perform a subsea completion at this unprecedented depth. It also included the installation of the FPSO host unit and the deepest mooring system (1,420 meters depth). This was the deepest installation of flexible lines and control umbilicals. All of these were in record water depths for their categories and the FPSO II was the first floater fully moored with polyester ropes."

Since then, Petrobras has installed and brought into operation the world's first deepwater electrical submersible pump (ESP) in a well located in 1,109 meters depth. This project involved the use of a guidelineless horizontal tree (GLL-WCT), a special 9-km electrical cable and power connectors, as well as a subsea transformer.

Agostini continued: "This ESP project, is also a good example of how we implement new technology. It was developed together with our supply partners, lab tested, then tested in shallow waters in Campos for about three years, and now it is working adequately 1 km below the surface of the ocean. Our R&D people feel confident it is ready for long tie-backs in ultra-deepwater." Work is also underway on multiphase pumping systems and ultra-deepwater (beyond 2,000 meters) horizontal and other trees, just to mention a few projects. A rigid export riser is about to be installed (J-Lay) and connected to a floating system for the first time and drill-tubing risers are being introduced for long duration production testing. What is believed to be the world first use of the Taut Leg anchoring system, with fixed VLA anchors, has just been installed in the P-27 FPS in the Voador Field, northeast of Marlim.

Copyright 1998 Oil & Gas Journal. All Rights Reserved.