The multi-billion barrel Buzios
Depending on the search engine you use, Búzios comes up as either a conch or whelk. Conch might be the more appropriate, given its association with use as a horn; Petrobras' Búzios field in Brazil deserves a lot of noise. Elaine Maslin takes a look.
by Elaine Maslin
FPSO-74: Petrobras AgencyPhoto by André Ribeiro / 2019 April 1st
Located in the Santos Basin pre-salt, it's been described as the largest deep-water oil field in the world, second only to Tupi (another Santos Basin, pre-salt giant). According to Brazilian oil regulator ANP's data, it pumped an average of 569,648 barrels per day back in July and is expected to hit 2 million barrels of oil equivalent per day by the end of the decade.
"With four FPSOs each of 150,000 barrels per day capacity already producing and another similar FPSO on the way, and with the project perhaps ultimately hosting another half dozen more such FPSOs, Búzios certainly qualifies for the major global tag," says Readul Islam, research analyst at consultancy Rystad Energy. It's a giant, relatively new on the scene, and double the size of initial estimates.
A giant discovery
The Búzios field was discovered in 2010, about 180km off the coast of Rio de Janeiro city in 1700-2100m water depth. Petrobras acquired the exploration rights to six blocks in 2010, the largest of which was Franco, on which it agreed a contract, known as ToR, to produce 3.1 billion boe for US$27.6 billion.
It was a lot of cash at the time, but came on the heal of an already successful exploratory campaign in the Santos Basin pre-salt, which had uncovered "accumulations of gigantic proportions," including Tupi (discovered in 2006) and Sapinhoa.
"The geological knowledge of Play Pre-salt at that time and the history of discoveries, already pointed out to a similar path for the block where Búzios field is located," says executive manager of Búzios, Marcio Kahn. However, Búzios also stood out. "A set of features that surprisingly differs Búzios field from the others is the presence of considerable hydrocarbons volumes in relatively older layers, with higher thicknesses and in reservoirs with higher porosities and permeabilities, resulting in extraordinary productivity rates."
Following two exploration wells, an extended well test, and 3D seismic data acquisition, Búzios was named and declared commercial, with recoverable volumes estimated to be more than double the 3.1 billion boe contracted volume.
Deepwater OBN records
The scale of the field is enormous; it spreads over an area of about 850sq km – similar to 10.5 American Gulf of Mexico standard offshore blocks, according to a Petrobras paper presented at OTC earlier this year, with 2100m salt to drill through and 6000m total depth. Búzios' scale meant it was the subject of "the largest 3D ocean bottom node project in deep water, covering 2,739sq km, with 6,650 node positions spaced at 500 m, and 1,100 shots, carried out over a year, from 2018," says the OTC paper.
It also meant multiple FPSOs to produce it, even under the initial ToR contract. Six were planned initially, but thanks to high productivity rates during appraisal, that was reduced to five 150,000 bpd units, producing from up to 68 wells (36 producers and 32 water alternating gas (WAG) injection wells). By 2019, after declaring commerciality in 2013, Petrobras had brought four owned FPSOs, Búzios 1, 2, 3, and 4 (aka P-74, P-75, P-76, P-77), into production on the field, spread moored in about 2200m water depth. They came onstream within just 11 months of each other, through April 2018 to March 2019).
Crosshead Fast ramp-up
"In order to manage four FPSO start-ups in such a short period of time, it was critical to have both human and physical resources," says Jaime Turazzi, general project manager of Búzios. "First, taking advantage of Petrobras' size and contracted fleet, we were able to properly allocate mooring vessels in a timely manner, as soon as the production facilities were ready to go. Also, having flexible lines in the subsea layout facilitated the process to accommodate fluctuations in each of the project's schedules and demand for critical resources. And finally, Petrobras' technical team onboard these units, making sure our commissioning and start-up activities were done with the expected quality and safety standards."
Petrobras had also built knowledge of the field upfront, by drilling at least two appraisal wells where each production system would be installed, and an extended well test and three early production systems with monitoring wells, to improve reservoir dynamic modeling. A common, basic design of wells, subsea systems, and FPSOs that could cope with variations in fluids, contaminants, well location, etc. was also developed. Existing standards already applied to other pre-salt fields were also used where possible, to reduce any need to qualify new equipment.
"Petrobras applies standardization to all aspects of our projects, from well design, to subsea equipment and FPSOs," says Turazzi. "The main benefits that we can capture value in our projects are associated with interchangeability between wells, cost reduction and learning curves across the whole production system."
Búzios wasn't all smooth sailing, however. "There were a lot of challenges, and it's hard to name just one," he says. "The ocean bottom node (OBN) [seismic data] acquisition occurred at the same period we were deploying the four FPSOs offshore, and, due to that, the acquisition was adjusted several times to avoid conflict with support vessels. Initial planning defined acquisition going north to south in the field, but afterwards, we started from the north, going south and then ending up at the central region.
"Aside from the conflicts with the operations of support boats for the launching of anchors, there were also offloading operations of the platforms in operation. A precise and fine-tuned strategy was necessary so that the quality of the nodes survey was the best possible. In addition, the nodes operate with batteries that run out in 60-70 days, at most. The survey, due to its dimensions, often forced us to place a second and even a third node so that we could obtain records with the necessary continuity. In other words, planning the survey with battery depletion was also a winning strategy exercise. This was mainly due to the size of the survey, which until then was unprecedented in the world."
"Other issues were the sea conditions we had to deal with (since our survey had a delay compared to the schedule and did not occur at the best time of the year) and the sighting of mammals (dolphins and whales) when operations had to be halted," adds Turazzi.
"In the wells department, one important challenge was to drill the reservoir and execute the completion, while facing severe fluid losses. Some locations were only possible to drill using managed pressure drilling and Petrobras has been an important player on this topic, with a large number of wells already drilled using underbalanced fluid and contributing to API Standards on this matter. It was implemented in the most complex scenarios to make it possible to achieve final depth. Also, an open hole intelligent completion scheme with decoupled string was developed to make the completion possible at this scenario of severe fluid losses."
Well construction learning curve
The biggest success on the project, says Turazzi, was the well construction learning curve, achieving "consistent results, by automation and digitalization of the workflows, operational procedures advances, by well design improvements, using open hole intelligent completions, managed pressure drilling, well monitoring in real-time, advances in cementing operations and lean diameters drilling with high-performance drillbits."
Another success was in the subsea arena. "Búzios had the first water and gas simultaneous injection, through ultra-deepwater manifolds," says Turazzi. "It was also the first application of an optimized 20-line spread mooring FPSO in ultra-deep water. A new riser system configuration development approach was put in place (using the largest torpedo piles ever used), leading to expressive cost savings and a higher production/injection flow rate per well was achieved thanks to the first use of an 8in production flexible line (instead of 6in) in an ultra-deep water definitive project."
Brazil's most productive well
The results so far have seen some notable achievements, such as Brazil's most productive well, BUZ-10, reaching 63,000 bpd. P-75 FPSO has reached a plant clearance limit of 169,000 bpd, with just four producing wells, and it and P-76 FPSO reached full capacity in just eight months. A daily production record of 674,000 bpd was reached on July 13, this year.
All four FPSOs – and the future units – have CO₂ capture and reinjection, to reduce emissions, but also aid enhanced oil recovery. Each unit also has flaring gas recovery systems, to reduce gas flaring. The fifth, a leased FPSO, Almirante Barroso, a similar size to the first four, is being built by Modec, and is due to start production in 2022 as part of the initial development of the field.
Yet more FPSOs
Yes, there's more to come. In 2019, as the last of the first four units was coming on stream, the state auctioned the additional volumes proven in the field, with Petrobras and its partners winning the so-called ToR+ prize. That gave the firm the keys to unlocking all the estimated recoverable reserves it had discovered. It also meant more FPSOs – up to seven more, in fact, which is expected to help increase the drainage rate at Búzios three-fold, from 750,000 bpd to 2 million bpd. To do this, Petrobras is going bigger, with the next tranche of FPSOs having 180,000-225,000 bpd capacity.
Work is already well underway. The sixth FPSO, the Almirante Tamandaré, being built by SBM Offshore, is under construction and due for delivery in 2024. Almirante Tamandaré has been tagged as one of the largest oil-producing units operating offshore Brazil and one of the largest in the world. It's set to have 250,000 bpd water injection capacity and a minimum 1.4 million bbl storage capacity.
FPSO-76: Petrobras Agency
"As we better understood the reservoir and its productivity, associated with our process and naval engineering capabilities, Petrobras increased the size of our standardized hull, paving the way to larger production facilities, bringing better economies of scale to our projects, and increasing their profitability," explains Turazzi.
The seventh unit, P-78, is being built by Keppel Offshore and Marine and Hyundai Heavy Industries, with Korea Shipbuilding & Offshore Engineering working on the hull. P-79, or unit eight, is being built by a consortium of Daewoo Shipbuilding & Marine Engineering and Saipem. These two, seven and eight, are both due in service in 2025, and will both have capacity to pump 180,000 bpd each and process 7.2 million cubic meters of gas per day. Bidding on unit number nine (P-80) started earlier this year, with the contract including the potential for two further units, P-81 and P82.
Innovation on ToR+
"Innovation is a core value within Petrobras, and we are looking into many new technologies to apply to our Búzios ToR+ projects," adds Turazzi. "We can highlight that Búzios field, when at full capacity, will be the largest offshore carbon capture and reinjection asset in the world. Also, the ToR+ wells include innovations such as open-hole hydraulic intelligent completion for three zones; electric intelligent completions, and electric downhole safety valves (DHSV); advances in the top hole section targeting to execute slender wells and optimize the post salt section.
"Subsea, Petrobras is developing a new riser support system, both for flexible and rigid risers, enabling a considerable reduction in diver-assisted operations and (achieving) cost savings associated to the feasibility of steel lazy wave risers pull-ins in keel hauling with minimum impact on the FPSO design. As for the FPSOs, the TOR+ will receive the largest vessels owned and leased by Petrobras (225,000 bpd/12 million m³/d), increasing value added to Búzios field development. They also considerer solutions to improve energy efficiency and technologies to reduce greenhouse gas emissions."
The scale of Búzios is immense. So much that partner CNOOC recently asked to exercise an option and acquire an additional 5% stake in production rights for the field, $2.08 billion.
"Petrobras is extremely pleased with Búzios development. It is our main asset, both in terms of value and volume in place," adds Kahn. "And we place a lot of effort to keep our plans for Búzios on track, and take a lot of pride to mention that we have achieved all of main milestones for ToR+ even through the pandemic."