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Proceedings of the 30

th

International Conference on Ocean Offshore and Arctic Engineering

OMAE 2011

June 18-24 2011 Rotterdam Netherlands

OMAE2011-50167

INSTALLATION OF A SUBMERGED BUOY FOR SUPPORTING RISERS (BSR)

SYSTEM IN CAMPOS BASIN SITE

Jairo Bastos de AraújoPETROBRAS - E&P

Rio de Janeiro, RJ, Brazil

[email protected]

José Carlos Lima de AlmeidaPETROBRAS - E&P

Macaé, RJ, Brazil

[email protected]

Antonio Carlos FernandesLOC & LabOceano/COPPE – UFRJ

Rio de Janeiro, RJ, [email protected]

ABSTRACTThe BSR (Buoy for Supporting Risers) concept is

composed by a submerged buoy anchored to the sea bottom by

tethers and intended to support risers coming from the bottom

(probably SCRs – Steel Catenary Risers) and going to thefloating platform (probably with flexible jumpers). For the case

under analysis here, the main dimensions of the BSR prototype

are 27.2 m length x 27.2 m width x 5.0 m depth. The paper

describes all final full scale installation step so that the BSR

may be considered a suitable technology. The installation

indeed was the great challenge of this design due the size of the

hull. The present work also evaluates numerically and

experimentally a specific new manner to install the BSR with

the support of auxiliary mooring lines among with the four

tethers connected to it. One of the installation premises was to

make use of Anchor Handling Supply Vessels instead of Crane

Vessels. After this numerical analysis, the work went on by

performing model tests that simulates the operation in a deepwater model basin using 1:40 scale. The model test anticipated

several problems such as the chain stopper weakness in the

operation and others as discussed in this paper. As a conclusion

the work was devised the most important parameters during the

system installation and suggested ways to improve the

methodology. In November 2009 the BSR was installed in 500

m of water depth at Congro field location, Campos Basin,

offshore Brazil. The tethers were adjusted in January 2010 and

in March 2010 two risers were installed. Thenceforward the last

edge of this knowledge was considered over passed.

INTRODUCTIONIn the last years the oil extraction in Brazil has

occurred in deep and ultra-deep waters (more than 2,000 m). In

that condition the risers (even the SCRs) suffer larger tensions

due to the weight, current and wave direct actions and theoscillatory motion of the connection point. An alternative to

mitigate this problem is to use a submerged buoy system for

supporting risers and referred here as BSR. The BSR scheme is

shown in Figure 1.

Figure 1 - Schematic view showing the BSR system.

Proceedings of the ASME 2011 30th International Conference on Ocean, Offshore and Arctic EngineeringOMAE2011

June 19-24, 2011, Rotterdam, The Netherlands

OMAE2011-50167

Copyright © 2011 by ASME

ownloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 11/25/2014 Terms of Use: http://asme.org/terms

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The hull itself is composed of steel cylindrical

members, anchored to the sea bottom by tight tethers and the

connection to the Floating Production Unit is made by jumpers

of flexible lines. It is well suited to support SCRs.The BSR works as an intermediate buoyant element for

the hybrid risers system, and avoids the large oscillatory

motions at the connection point since the environment action on

BSR itself is much smaller since it is below the sea level (75 m

for the case study here). This conception has been numerically

analyzed and tested since the 90´s. However the BSR

installation was considered an open issue until 2009.

A prototype BSR was fabricated in 2004, as showed in

Figure 2. Despite the adequate behavior obtained in the lab

tests, numerical analysis one had to close a main issue: how to

put a big hull below the sea level and keep it by tethers? So an

installation procedure was first developed by PETROBRAS.

Then several model testing were performed ocean basin ofLabOceano/COPPE/UFRJ, Rio de Janeiro, Brazil, to seek for

improvements of installation procedure. The references [1] and

[2] present the lab results and in 2005 the first BSR installation

takes place in Campos Basin with some good and partial results.

Figure 2 – BSR at the shipyard.

In 2008 another installation procedure was prepared

and the last lab test and numerical analysis detailing the phases

of the procedure were done and presented in references [3] and[4].

Finally in November of 2009 the BSR is installed in

500 m of water depth, at 75 m below the sea level, at Congro

field, Campos Basin. The job developed and the final tasks on

the BSR installation are discussed afterward.

GLOSSARYAHTS: Anchor Handling, Towing and Supply Vessel.

SV: Survey Vessel equipped with ROV.

ROV: Remote Operated Vehicle.

DW: Dead Weight.

MT: Metric tons.

FPU: Floating Production Unit.

KS: Hook modified to work like a subsea connectorand disconnector.

Pelikelo: Subsea connector that can open under

tension.

BSR DESCRIPTION AND ITS MAIN COMPONENTS

The first BSR prototype developed by PETROBRAS is

showed in Figure 2. Their main characteristics are presented in

Table 1.

Table 1 – Main Properties of the BSR.

Length 27.2 mBreadth 27.2 m

Depth 5.1 m

Diameter of each

cylinder (*)2.4 m

Weight in air 287 MT

Net Buoyancy 619 MT

Nb. of ballast tanks 24

(*) The stern of BSR is characterized for existing two cylinders.

One connected above the other.

Chain stopper and chain sheave (see Figure 3)

constitute a passive system used to adjust the BSR tethers. The

chain stopper has a flap that restricts the chain in one direction

and the chain sheave is a pulley with free rotation to support the

chain.

Figure 3 – Chain Stopper and Chain Sheave of the BSR.

The BSR has a ballast system that is used to compound

the BSR weight during the installation. The system was

designed to work with compressed air and sea water. Each

ballast tank has two valves.



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Two receptacles were installed on the stern and bow of

BSR to connect risers and jumpers lines respectively.

The BSR has a set of four tethers, anchored at the soil

by torpedo anchor. Tethers were used to assist the BSRinstallation before work with its specified function. Chain and

wire rope compounds the tethers and its characteristics are

showed in Table 2.

Table 2 – Tethers Properties.

DESCRIPTION Diameter Length Type

Bottom Chain 76 mm 55 m R3

Wire Cable 78 mm 300 m Six Strand

Top Chain 76 mm 70 m R3 Studless

Four auxiliary mooring lines were used to support the

BSR installation and keep it on its right coordinate during thehook up of the tethers. These mooring lines were also anchored

at the soil by torpedo anchor and its composition is shown in

Table 3.

Table 3 - Auxiliary Mooring Lines Properties.

DESCRIPTION Diameter Length Type

Bottom Chain 76 mm 340 m R3 Studlink

Wire Cable 87 mm 850 m Six Strand

Top Chain 76 mm 100 m R3 Studless

Four dead weights were fabricated and used to pull the

BSR below the sea level and towards its installation depth andalso to facilitate the hook up of tethers. Each dead weight has

40 MT in the sea water.

PREPARATION OF THE BSR PRIOR TOWING

BSR was prepared on shipyard in order to facilitate its

installation and transportation. The main tasks made were:

• Installation of the towing system.

• Installation of 08 top chain segments. Two in each

corner or 70 m of tether and 30 m of auxiliary mooring

line.

• Ballasting of 06 tanks.• Checking the navigation lights.

• Flushing of the ballast and vent lines.

INSTALLATION OF THE BSR

For better understanding of the installation procedure the

following phases have been devised as described below.

Phase 1: Some auxiliary mooring lines and tethers

components were pre-installed and laid down at the sea floor.

The bottom chain of tethers was divided in segments of 25 m

and 30 m. All 25 m were pre-set with the torpedo with the KS

shackle- pick-up buoy system on the free extremity, as shown in

Figure 4.

Figure 4 – Bottom Chain (25 m) pre-set.

Phase 2: The BSR was towed from Guanabara Bay,

Rio de Janeiro, to Campos Basin site (see Figures 5 and 6).

Four AHTS and one SV were standing by with all remaining

auxiliary mooring lines and tethers components to start the

operation.

Figure 5 – BSR at site for installation.



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Figure 6 – BSR at surface site for installation.

Each auxiliary mooring line pre-set was fished on thesea bottom by the AHTS and connected to the BSR through

Pelikelo. So the towing vessel was released. The lengths of the

top chain were adjusted on the deck of the AHTS.

Phase 3: With BSR safely moored with the four

auxiliary mooring lines the tethers hook up operation began.

Each remaining tethers lengths, as well their respective DW,

were on board each of the four AHTS. The tethers loaded in

each one of four AHTS were connect in their respective 70 m of

top chain pre-installed on BSR and paid out until the 30 m of

bottom chain. Then the DW was connected on the 30 m of

chain triplate through a sacrifice wire cable of 2 in X 4 m, a KS

on the 30 m of chain free end, the AHTS work wire on the DWand the system was launched on the water as showed in Figure

7.

Figure 7 – Line configuration for the descent of BSR.

The descent of the BSR until its required depth was

conducted simultaneously by the 04 AHTS as showed in Figure

8. Some steps that correlated the distance between AHTS andBSR vs. length of the work wires were followed as Table 4.

Figure 8 – AHTS arrangement for the descent of BSR.

Table 4 – Correlation Distance vs. Work Wire Length.

STEPSAHTS-BSR

Distance (m)

Work Wire

Length (m)

01 220 160

02 160 300

03 160 325

04 160 440

05 40 440

06 40 465

Once the DWs reached near to the sea bottom, theirs

placement were guided by the ROV in order to facilitate the

connection between the KS hook and its shackle (see Figure 9).

Figure 9 – KS hook connected on its shackle.



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The ROV carried out the four KS connection, cut the

sacrifice wire cable and later on released the four auxiliary

mooring lines by opening the Pelikelos. Figure 10 shows the

final appearance of the BSR system after its installation.

Figure 10 – BSR installed.

It was necessary to adjust the length of 03 tethers due

to high trim and heel angles on the BSR after tethers hook up

operation. This adjustment was done using 03 DW with the

right leg length connected at auxiliary mooring line segment

hanging off on BSR corner. When the BSR was in the correctlevel of trim and heel the 03 tethers top chains were pulled out

trough the respective chain stopper, as per Figure 11.

Figure 11 – Tethers adjustment by pulling the top chain.

Two months later two risers were installed on the BSR

(see Figure 12) to validate the procedure and the technology as

presented in reference [5].

Figure 12 – Two risers installed on the BSR.

CONCLUSIONS

This installation procedure developed and carried out,

including the equipment, vessels and materials selected, proved

the technical and economical feasibility of the BSR technology

The installation in full scale experience clearly shows the

complete feasibility of the BSR concept. This may explain whythe two BSR concepts were chosen by the market in a recent

design competion.

The pre-salt area in Campos Basin is a scenario for the

BSR technology since it is a deep water scenario with a FPSO

as the choice for the FPU.

The possible trim and heel angles requires care during

the descent of the BSR stage. It must be addressed in later

stages.

The lengths of the auxiliary mooring lines and tethers

segments must have a fine control.

The adjustment system of the tethers must have proven

capabilities.

The tolerances for BSR trim and heel angles must be

defined in the design phase.

The hull of the BSR can be made by steel plate,

synthetic foam or a combination of both.



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ACKNOWLEDGMENTSThe authors acknowledge Petrobras and the CNPq (the

Brazilian National Research Council).

REFERENCES[1] Fernandes, A.C., Santos, M.F., Sales, J.S., Araújo,

J.B., Almeida, J.C.L., Diniz, R. and Rangel, M.; “Model Test

and Numerical Simulations for the Development of the First

Full Scale Riser Support Buoy (BSR)”- XVIII International

Congress of Mechanical Engineering (COBEM); Ouro Preto,

Brazil, November 6-11, 2005.

[2] Fernandes, A.C., Almeida, J.C.L., Araújo, J.B., Rangel,

M., Santos, M.F. and Sales, J.S.; “Numerical Simulation and

Experimental Analysis for a Riser Support Sub-surface Buoy” –

Rio Oil & Gas, Expo and Conference, Rio de Janeiro, Brazil,IBP241_04, October 04-07, 2004.

[3] Fernandes, A.C., Almeida, J.C.L., Araújo, J.B.,

Franciss, R., Rangel, M., Merino, J.A. and Sales, J.S.;

“Parametric Evaluations of the Buoy Supporting Riser (BSR)

Installation” - 1st Marine Operations Specialty Symposium 2008

(MOSS2008); paper MOSS-60, Singapore, March 5-7, 2008.

[4] Fernandes, A. C., Merino, J. A., Silva, A. R., Araújo, J.

B., Almeida, J. C. L., and Franciss, R.; “Analysis of the

Installation of a Buoy Supporting Risers (BSR) by Numerical

Modeling and Model Testing” - Dtec2008 - Deepwater

Offshore Technology Symposium 2008, Shangai, China, November 17-19, 2008.

[5] Franciss, R., Almeida, J.C.L., Araújo, J.B., Gonzales,

E.C., Fernandes, A.C., “Alternative Method of Buoy Supporting

Riser (BSR) Installation”, OMAE paper 49862, June 18-24,

2011, Rotterdam, Netherlands.


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