PETROBRAS LOGS STRING OF MILESTONES OFF BRAZIL

Petroleos Brasileiro SA continues to increase production and advance deepwater technology in the Campos basin off Brazil.

Petrobras recently placed on stream the first of four wells in the pilot early production project for Bijupira and Salema oil fields in the Campos basin off Rio de Janeiro. Petrobras used new technology to lay a hybrid rigid/flexible pipeline to transport crude from the two fields that set a world record for deepwater pipelines and resulted in significant cost savings.

Meantime, rising production from the Campos basin's Albacora and Marimba fields has pushed Brazilian oil production to a record high.

In addition, Petrobras drilled another sizable oil discovery in the basin.

BIJUPIRA, SALEMA ON STREAM

Petrobras started production from the Salema/Bijupira pilot system at 7,500 b/d in a project that cost about $83 million.

Plans call for production to build to 20,000 b/d of 28-30 gravity oil and 8.75 MMcfd of gas by January. The two fields be in water depths of 1,640-2,460 ft.

Petrobras is using the recently upgraded Petrobras XIII semisubmersible as the SS-20 floating production system (FPS) in Bijupira field to handle production from both fields. The FPS is installed in 2,066 ft of water.

Some Salema/Bijupira oil is shipped from the FPS via pipeline manifold installed in Corvina field to a fixed platform in shallower water in Cherne field using a 17 km, 8 in. pipeline. Petrobras laid the line with an innovative hybrid rigid/flexible recovery/lay method from the FPS to the Corvina pipeline manifold.

The rest of Salema/Bijupira crude moves via pipeline manifold in Corvina field to a nearby single point mooring buoy.

Salema/Bijupira gas moves through a 10 in., 21 km pipeline to the Marimba field platform.

When all wells in the pilot are on line, field production will be handled by two monobuoys installed near the Corvina pipeline manifold.

The pilot was installed to gather reservoir data, provide information for design of the final production system, and develop cash flow estimates for both fields. Five wells have been drilled in the two fields, which are geologically similar to the nearby Pirauna-Marimba complex.

Petrobras estimates lifting costs at $8/bbl, including capital and operating outlays, spread over 10 years. The total pilot project cost of $83 million includes well completion, FPS conversion, purchase of four wet Christmas trees, and 12 km of 4 in. gathering lines.

Reserves are estimated in Bijupira at 120 million bbl of oil and 56 bcf of gas and in Salema at 35 million bbl and 28 bcf.

HYBRID RECOVERY APPROACH

Petrobras employed a reduced recovery method to lay the pilot project's rigid/flexible hybrid line from the FPS to the pipeline/manifold.

The method entails recovering a prelaid steel export pipeline coupled to a 16 m long flexible jumper using a hybrid connector. The flexible portion of the prelaid line provides a J configuration connected to a flexible riser tied back to the FPS.

Connection of the rigid portion of the pilot system's pipeline to the SS-20 took place at a depth of 2,312 ft, which Petrobras claims as a world record for subsea pipeline installation. The record won't stand long, because Peotrbras plans next year to lay two more oil pipelines and a gas pipeline using the hybrid system technology in 2,886 ft of water to export production from the Marlim field pilot project.

The new diverless pipelay/recovery method also was intended to deal with considerations of safety and reliability, as well as minimal development, qualification testing, and surface vessel support with few or no modifications, said Marcelo Jose Barbosa Teixeira, Petrobras production department engineer.

HYBRID PIPELINE BENEFITS

Using the reduced recovery hybrid lay method saved Petrobras $12 million compared with the cost of laying an entire flexible export pipeline.

Teixeira also cited these other operating and economic benefits of hybrid pipelines:

• Hybrids using long segments of rigid fine offer cost savings over conventional large diameter export pipelines.

• Installation of rigid line segments does not depend on the presence of a catenary anchored FPS. This flexibility allows the segments to be installed without interfering with the project's critical path and thus minimizes lay vessel downtime and lowers day rates,

• All connections are made aboard the pipelay/recovery vessel. This diverless approach thus can be used in ultradeep waters.

• The flanged connection is easily performed as a diverless pull-in operation, making the special connectors, structures, and tools needed for diver assisted connections unnecessary.

• The operation is fully reversible, allowing recovery of the flexible line for use in other projects or re-laving in other directions, depending on relocation of the FPS.

• The procedure reduces final project hookup time and can be used to repair ultradeepwater pipelines.

COMPUTER PROGRAM

For the new recovery/lay technology Petrobras developed a computer program with calculations based on the latest version of an internationally recognized flexible pipe configuration analysis code, Flexan F, derived from the standard time domain, catenary based, finite element analysis program Flexan D.

Flexan F has the added capabilities to model beam elements together with catenary elements and respond to the challenge of modeling cables, flexible pipe jumpers, and steel pipe along with concentrated masses in a standard time domain approach.

It developed a recovery and re-lay table calculated in a quasistatic mode to limit computing time and analysis.

However, full time dynamic runs were performed to evaluate response of the suspended steel pipe during the onboard connection of the jumper to the flow line using I year and 10 year projections. This allowed Petrobras to ensure that weather limitations would not be exceeded during the operation by determining the maximum acceptable acceleration of the pipelay vessel bow.

The reduced-recovery table providing parameters needed for offshore utilization proved acceptable from a vessel standpoint, for reasonable power output, and from the steel pipe standpoint, Teixeira said.

PRODUCTION RECORD

Petrobras' crude oil production reached 710,232 b/d in October with start-up of more wells in Marimba and Albacora fields.

That record is expected to fall in coming months, when Caravelas field in the Santos basin starts up. Initial production is expected to be 10,000 b/d.

Petrobras achieved the record production level by increasing productivity of Campos basin fields, which produced at 97.1% of capacity highest in the state owned petroleum company's history.

Brazilian production rose by about 10% during the 12 months ended in September, or an increase of more than 65,000 b/d.

At the same time, Petrobras jumped its reserves estimate by about 4% during first half 1993. Current proved reserves in water depths to 1,000 m total 4.6 billion bbl of oil equivalent (BOE). If probable reserves in water depths of 1,000-2,000 m are considered, that number jumps to 11 billion BOE.

CAMPOS DISCOVERY

Petrobras drilled its 4 RJS 396D wildcat about 10 km from giant Marlim field and 100 km offshore in 2,296 ft of water.

The discovery well's productive capacity is estimated at 3,000 b/d of oil.

Pay sands are at 8,200-256 ft. Initial estimates peg potential reserves at 20 million BOE.

It is the 1,000th well Petrobras has drilled in the offshore Campos basin since exploratory drilling started there in 1971.

Copyright 1993 Oil & Gas Journal. All Rights Reserved.