Steely Business In The Basin

11 April 2010 (Last Updated September 1st, 2020 13:31)

Subsea 7 overcame many technical challenges to complete Brazil's largest reeled steel pipeline installation project. Senior project engineer Cesar Bartz discusses the subsea engineering and construction company's work on Shell's Parque das Conchas (BC-10) development.

Steely Business In The Basin

South America is home to almost a tenth of global crude oil reserves and 4% of total natural gas reserves. Brazil itself recorded more than 12.7 billion barrels of crude oil reserves and 11,500bcf of natural gas reserves in 2008. Moreover, recent offshore discoveries could potentially transform the country into one of the most significant oil exporters worldwide.

Subsea 7 has worked extensively across the region and recently completed one of its most challenging projects in Brazilian deep waters. In 2009, the subsea engineering and construction company concluded the pipeline installation activities for the Parque das Conchas (BC-10) development, which is operated by Shell on behalf of the BC-10 Joint Venture, with Petrobras and ONGC as collaborators.

Situated 120km southeast of the city of Vitória, north of the Campos Basin, the Parque das Conchas project comprises four fields: Ostra, Abalone, Nautilus and Argonauta, located at water depths of 1,700-2,050m.

Production from BC-10 started on 13 July 2009 and will further develop to include nine producing wells and one gas injector well. The FPSO Espírito Santo, located in the field, is capable of producing 100,000bopd and can process up to 3.5 million cubic metres of gas in the same timeframe.

Subsea 7's involvement in the BC-10 pipeline installation included: the fabrication and installation of 11 flowlines totalling approximately 130km and incorporating three gas pipelines and oil pipelines; the fabrication, welding and installation of seven Steel Lazy Wave Risers (SLWRs) totalling 21km; the transportation and installation of three dynamic and two static umbilicals totalling approximately 55km; the installation of four manifolds; the manufacturing and installation of 25 rigid jumpers; and the installation of more than 60 flying leads.

Technical challenges

Of the challenges overcome throughout the BC-10 project, many were linked to welding and automatic ultrasonic testing inspection, pipe wall thickness variation and the intricacies of building a complex riser system for ultra-deepwater.

"The Seven Seas' portion of the project included setting up two artificial lift manifolds and two production manifolds."

Installation analysis for the BC-10 pipelines and welding development for fabrication of the pipelines required a concerted effort from the team. Several finite element analyses were performed to ensure the reeling and straightening process would not harm the fatigue life of the risers.

In addition, matching the large wall thicknesses variation with the fabrication tolerances of the linepipes led to the individual measurement of all pipe ends and segregation of several dimensional groups of the same riser. Following grouping, all riser bores were machined to tight tolerances to allow a maximum hi-lo as low as 0.5mm.

The process of treating each linepipe as an individual item on a huge fabrication list was performed for no less than 15,000 pipe joints. Over a period of 15 months the BC-10 pipes were received, measured, grouped, machined, welded, inspected and field-joint coated in what has been, to date, the largest reeled steel pipeline installation project ever performed in Brazil.

Subsea 7 worked to strict technical requirements on the SLWRs. With enormous stress to be exerted on the risers, the project team had to ensure that the welding would meet the required quality to assure the 30-year field design life cycle. This was achieved by using the automatic tungsten inert gas (TIG) welding process; TIG welding is known for its high quality, contributing to the production of welds with low reject rates.

According to Paul Alexander, Subsea 7 project manager, these challenges were successfully overcome due to the wide-ranging expertise of the team involved.

"All pipeline fabrication and installation engineering was performed by Subsea 7 involving a lead team located in Brazil, supported by personnel from other global offices, as required," he explains. "This ensured that an integrated international team was in place, with the required qualifications, drawing on shared learning and experiences from throughout the company."

Star performers

The use of Subsea 7's flagship vessels, Seven Oceans, a rigid pipelay craft, and Seven Seas, a pipelay and construction vessel, was another important factor contributing to the success of the BC-10 operations.

"FPSO Espírito Santo is capable of producing 100,000bopd and 3.5 million cubic metres of gas."

Delivered in 2007, Seven Oceans is designed to operate in deepwater across the globe. The 157m-long ship is fitted with a main reel capable of carrying 3,500t of rigid steel pipe that itself weighs 1,000t. Seven Oceans also holds a pipelay tensioner with a 400t capacity, a 400t capacity deepwater crane and has the capacity to lay pipe at water depths of up to 9,000ft.

A lay ramp system is permanently installed for the deployment of a range of rigid pipelines of 6-16in, and the vessel can accommodate up to 120 crew members.

Rather than holding a rigid reel and lay tower, Seven Seas, which was completed in 2008, is equipped with a highly versatile multi-lay tower and twin underdeck carousels. With a top tension capacity of 400t, the vessel can operate in flexlay and rigid J-lay mode in water depths up to 3,000m. In addition, its 1,750m² deck area and 400 crane capacity mean Seven Seas is suited to installing the large structures associated with deepwater subsea field developments.

"The BC-10 development enjoyed the single honour of being the first Subsea 7 project to welcome both of the company's new flagship pipeline installation vessels, Seven Oceans and Seven Seas, to perform installation of the pipelines and associated subsea equipment," notes Alexander.

A total of 770 vessel days were consumed to complete the project, and the installation was also supported by the Seisranger ROV support vessel over a period of 278 vessel days. A multipurpose offshore support vessel with a primary ROV function, the main work-class ROV is capable of operating in deepwater locations up to 2,000m, deployed through the vessel's centreline moon pool.

BC-10 operations

While 75km of 12m length coated X-60 and X-65 steel linepipes were being joined together forming 1km-long stalks in Subsea 7's Ubu spoolbase, located close to Vitória, the umbilicals were being loaded onto Seven Seas in Florida, USA. The vessel arrived in Brazil in October 2008 to start its assignment.

The Seven Seas' portion of the project included the setting up of two artificial lift manifolds and two production manifolds with a maximum weight of 231t. In addition, the BC-10 project was the first occasion on which Subsea 7 had installed umbilicals with an outer diameter of 220mm in water depths of up to 2,050m; a total of three dynamic and two static umbilicals of approximately 55km were put in place.

"All riser bores were machined to tight tolerances to allow a maximum hi-lo as low as 0.5mm."

The BC-10 project was one of the largest subsea jumper installation campaigns ever undertaken. 25 rigid jumpers, designed to connect the wells to the manifolds and pipelines, were manufactured and tested within the Companhia Portuária de Vila Velha facilities at the Vitória Port Espírito Santo before being transported to Seven Seas for installation.

This was the first time jumper manufacturing had been completed in Brazil and in order to guarantee that the dimensions and connector angles of the manufactured jumpers were correct, detailed metrology and pre-installation tests were conducted at the fabrication base by reproducing the actual dimensions for fabrication.

Seven Oceans also arrived in Brazil in early October 2008. The spooling activities took place at Subsea 7's Ubu Spoolbase where the SLWRs and flowline stalks were fabricated and stored and, on reaching the BC-10 site in 2008, the vessel began installation of the SLWRs and flowlines, laying the lines from the pipeline end terminations towards the FPSO location.

In total, Seven Oceans made 12 trips over the offshore campaign and Subsea 7's Ubu Spoolbase was of significant advantage in catering for this. Ubu is located only six hours steaming time from the field, which helped considerably with the project's schedule. It is the only operational spoolbase in Brazil and has been extensively used by Subsea 7 for several steel pipeline projects in the last five years, such as Golfinho, PDEG and Roncador.

Assembly of the SLWRs was a complex task. Across the 3km length of the dynamic section of the pipeline, several items had to be installed. In all seven risers, a total of 257 buoyancy modules weighing 2t each were installed to form the lazy-wave arches; the quantity varied from 25 buoys in the 6in gas export riser to 77 buoys in the 10in oil production riser. In each riser, a total of 1km of strakes and 200m of fairings were installed to suppress vortex induced vibration.

"Seven Oceans installed the entire subsea pipeline system including transfer of the SLWRs and flex joints to the FPSO."

Seven Oceans was also involved with the installation of the flex joints, an important milestone for the vessel. The installation engineering of the joints was a complex design activity performed by the project team, which included the development of a high-speed orbital tig welding process.

This work started with the positioning of the first of three forged pieces in the Seven Oceans' workstation and continued until the completion and transfer of the flex joint and riser to the FPSO.

Over an eight-month period, Seven Oceans installed the entire subsea pipeline system including transfer of the SLWRs and flex joints to the FPSO.

Local expertise

Subsea 7 has a wealth of experience working in Brazilian deepwaters. For a decade, the company has been involved in various subsea engineering, procurement, installation and commissioning projects in the area for major operators including Shell, Petrobras and StatoilHydro.

But Victor Bomfim, vice president for Subsea 7 in Brazil, is particularly proud of the company's efforts throughout the BC-10 project.

"We are delighted to have successfully delivered on the BC-10 project for Shell and its joint venture partners," he says. "It builds on Subsea 7's existing track record of working with leading operators for deepwater pipelay installation projects in Brazil.

This achievement is underpinned by well-established company roots, infrastructure in the region, an experienced locally based workforce, engineering expertise, effective project execution and a modern vessel fleet fitted with the latest technology. It reinforces our position as the Subsea partner of choice in Brazil."