Giant meandering channel evolution, Campos deep-water salt basin, Brazil

Submarine channels are conduits for sediment delivery to continental margins, and channel deposits can be sandy components of the fill in tectonically active salt basins. Examples of salt-withdrawal basin fill commonly show successions of sandy channelized or sheet-like systems alternating with more mud-rich mass-transport complexes and hemipelagites. This alternation of depositional styles is controlled by subsidence and sediment-supply histories. Salt-basin fill comprising successions of largely uninterrupted meandering-channel deposition are less commonly recognized. This begs the questions: can sediment supply be large enough to overwhelm basin subsidence and result in a thick succession of channel deposits, and, if so, how would such a channel system evolve? Here, we use three-dimensional seismic-reflection data from a >1500 km2 region with salt-influenced topography in the Campos Basin, offshore Brazil, to evaluate the influence of salt diapirs on an Upper Cretaceous–Paleogene giant meandering submarine-channel system (channel elements >1 km wide; meander wavelengths several kilometers to >10 km). The large scale of the channels in the Campos Basin suggests that sediment discharge was large enough to sustain the meandering channel system in spite of large variability in subsidence across the region. We interpreted 22 channel centerlines to reconstruct the detailed kinematic evolution of this depositional system; this level of detail is akin to that of recent studies of meandering fluvial channels in time-lapse Landsat satellite images. The oldest channel elements are farther from salt diapirs than many of the younger ones; the centerlines of the older channel elements exhibit a correlation between curvature and migration rate, and a spatial delay between locations of peak curvature and maximum migration distance, similar to that observed in rivers. As many of the younger channel centerlines expanded toward nearby salt diapirs, their migration pattern switched to downstream translation as a result of partial confinement. Channel segments that docked against salt diapirs became less mobile, and, as a result, they do not show a correlation between curvature and migration rate. The channel migration pattern in the Campos Basin is different compared to that of a tectonically quiescent continental rise where meander evolution is unobstructed. This style of channelized basin filling is different from that of many existing examples of salt-withdrawal minibasins that are dominated by overall less-channelized deposits. This difference might be a result of the delivery of voluminous coarse sediment and high discharge of channel-forming turbidity currents to the Campos Basin from rivers draining actively uplifting coastal mountains of southeastern Brazil. Detailed kinematic analysis of such well-preserved channels can be used to reconstruct the impact of structural deformation on basin fill.

Tectonic and Stratigraphic Evolution Based on Seismic Sequence Stratigraphy: Central Rift Section of the Campos Basin, Offshore Brazil

The rift section of the Brazilian basins represent the sedimentary record associated with the first stages of Gondwana break-up in the Early Cretaceous phase (Berriasian to Aptian). The rift succession of the Campos Basin constitutes one of the main petroleum systems of Brazil’s marginal basins. This interval contains the main source rock and important reservoirs in the Lagoa Feia Group deposits. The Lagoa Feia Group is characterized by siliciclastic, carbonate and evaporite sediments deposited during the rift and post-rift phases. Despite the economic relevance, little is known in stratigraphic terms regarding this rift interval. To date, most studies of the Lagoa Feia Group have adopted a lithostratigraphic approach, while this study proposes a tectonostratigraphic framework for the deep-rift succession of the Campos Basin (Lagoa Feia Group), using the fundamentals of seismic sequence stratigraphy. This work also aims to establish a methodological and practical procedure for the stratigraphic analysis of rift basins, using seismic data and seismofacies, and focusing on tectonicstratigraphic analysis. The dataset comprised 2D seismic lines, core and lithological logs from exploration wells. Three seismic facies were identified based on reflector patterns and lithologic data from well cores, providing an improved subdivision of the pre-, syn- and post-rift stages. The syn-rift stage was further subdivided based on the geometric patterns of the reflectors. Tectonics was the main controlling factor in the sedimentary succession, and the pattern and geometry of the seismic reflectors of the syn-rift interval in the Campos Basin allowed the identification of three tectonic systems tracts: (i) a Rift Initiation Systems Tract; (ii) a High Tectonic Activity Systems Tract and (iii) a Low Tectonic Activity Systems Tract.

A Safe and Cost Effective Diverless Method for Hull Wetted Surface Side Shell Repairs Executed On FPSO Fluminense

The Bijupira and Salema oil fields in the Campos Basin, Brazil, are tied-back to the FPSO Fluminense. The design life of FPSO Fluminense was 15 years, first oil was in 2003. In 2017, Shell as operator and partner Petrobras decided to execute a 5 year life extension project to extend production until 2023. Although the life extension project encompassed many vessel, moorings, and production facility renovation projects, this paper will focus on the repairs of cracks in the wetted surfaces of the hull. Crack repairs were executed during production operations using a novel methodology designed to eliminate the risks of diving operations, while significantly reducing the costs of the offshore hull repairs. Earlier attempts using traditional methods with divers to deploy cofferdams were unsuccessful due to the high safety risk of diving in the persistent 2-plus knot Brazil current. In early 2019, the operator and a team of engineering consultants concluded that a novel repair approach that eliminates diving operations was feasible. The concept methodology was developed, one element of which included positioning and securing a cofferdam over a cracked area of the FPSO side shell. The cofferdam was lowered from the FPSO deck while being guided into position and secured in place by guide wires passed through holes in the side shell. Water ingress into the void spaces was eliminated via a hot tap and winching system that penetrates the side shell from inside the tank. Following the concept development, a step-by-step procedure was written, vetted with the classification society and subsequently used in the tendering process to select an execution contractor. The selected execution contractor constructed a test tank that replicated the actual hull structure. The prototype was used to test the method at full scale, including procedures, communication protocols, and equipment. The learnings were incorporated into both the procedures and equipment. This process was repeated as a training exercise for the offshore personnel and HSSE leaders prior to offshore execution. The execution contractor was mobilized offshore in the first quarter of 2020 and successfully performed the hull repairs. The job was completed as planned, including removal and replacement of several independent sections of stiffened hull plating, which included both flat and curved surfaces. Based upon successful execution, this method has been proven to be a technology that can be used to eliminate the risks of diving and to significantly reduce the costs of future offshore hull repairs. This paper will address the methodical approach taken to develop and integrate the various elements of this novel technology developed jointly by the operator and consultants, as well as the phases testing, pre-mobilization surveys, project execution, and other activities that drive success.

Invasive Sun Coral Species Challenges Decommissioning of Structures Offshore Brazil

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30656, “Decommissioning of Subsea Structures in Brazil: Effect of Invasive Species and Genome Sequence of the Azooxanthellate Coral Tubastraea sp.,” by João Humberto Guandalini Batista, SPE, Repsol; Mauro Rebelo, Universidade Federal do Rio de Janeiro; and Giordano Soares-Souza, SENAI CETIQT, prepared for the 2020 Offshore Technology Conference, originally scheduled to be held in Houston, 4–7 May. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. Decommissioning of offshore assets in Brazil is subject to high levels of uncertainty because of Tubastraea, an invasive species of sun coral. This species has a high capacity for dispersion and recruitment and has been associated with the replacement of native species in rocky shores, exerting a serious effect on native biodiversity. The complete paper explores the biology of the invasive species, aiming to identify methods to eliminate or diminish its spread. The authors write that data generated in this study will foster the development of effective technologies in coral-species management, whether species are invasive or threatened. Introduction Originally from the Coral Triangle in the Pacific Ocean—a highly diverse region with hundreds of coral species—Tubastraea was first observed in the Campos Basin in the 1980s. Tubastraea sp. have high fecundity and growth rates with the ability to reproduce asexually, establishing very dense populations. This fast reproduction allows larvae to outcompete native species in both natural and artificial substrates in the sea. Sun coral is extremely resistant to environmental change. It has been found in shallow waters, sometimes exposed to air, showing tolerance even to short periods of desiccation. Recently, new species have been identified in Brazilian waters, heightening concern over the proliferation of sun coral. In the past, the common understanding was that subspecies coccinea and tagusensis were those found in Brazilian waters. However, recent studies dedicated to the research of the Tubastraea genus raised suspicion of the presence of diaphana and aurea, with the possible occurrence of hybrids as well. The preference of Tubastraea is to live in structures that are static or mostly motionless, such as production platforms, subsea structures, and drilling rigs. This trait has made sun coral a major challenge for the local oil and gas industry. While in the Campos Basin, the main objective is to decrease dispersion of already bioencrusted production units and subsea structures, in the Santos Basin, the goal is to avoid colonization in structures in operation or those scheduled to be installed soon. To further complicate matters, drilling and intervention vessels and rigs are contracted to service both basins. They work in dynamic-positioning mode, stationary around the production units and subsea structures for lengths of time that exceed the reproduction cycle time of the sun coral, allowing larval dispersion.

A Norwegian Oil Company Could Play a Key Role in Brazil’s Gas Transformation

Equinor could play a critical role in Brazil’s drive to boost its economy by opening up its gas markets. The Norwegian oil company operates two huge deepwater blocks with enough gas to lower prices in the country where big users pay some of the highest prices in the world. The development plan for one of those blocks, BM-C-33 in the Campos Basin, would deliver an average of 14 million m3/d of gas—about 15% of the country’s gas demand on a high-consumption day, which is about 92 million m3/d, based on data from Rystad. A second project in the heart of the presalt, Bacalhau, could become a model for how an international oil company can market gas successfully in the country’s richest oil play, the Santos Basin presalt. The gas potential in that play is also huge; the gas/oil ratio is high compared with other Brazilian fields but has largely been untapped. So far, Equinor and its partners in the projects have not committed to developing gas on either lease, but Equinor appears to be seriously considering doing so. The big question it needs to answer is what the gas market there will look like in a year or so. Brazil has set out to promote domestic gas supplies by ending Petrobras’ virtual monopoly in the pipeline business in favor of a less-regulated, competitive gas market. Equinor avoided gas sales at Bacalhau with an $8 billion Phase 1 plan that will use the popular practice of reinjecting produced gas. Gas reinjection maintains reservoir pressure and allows the development to comply with Brazil’s ban on routine flaring. Brazil’s energy regulator, ANP, said that when Equinor develops a plan for its second phase of development, the company needs to con-sider gas production. The role of gas market pioneer is the latest technical challenge taken on by Equinor in Brazil. Previously, it became the operator of an offshore heavy-oil field—Perigrino—and an aging giant—Roncador—both in the Campos Basin. While the Norwegian company has not promised to take on that role, it has a huge incentive to do so as the operator of Block BM-C-33, where most of the reserves are in the form of gas. The resource is estimated at 3 Tcf of gas and 700 million bbl of condensate, according to Offshore Technology. Equinor and its partners Repsol and Petrobras have developed a plan that would move the liquids by tanker from the platform, which is in water as deep as 2900 m, and build a pipeline about 200 km from there to shore. When asked about the status of the project, Geir Tungesvik, senior vice president for project development at Equinor, said the company is working to “improve the business case.” A Potential Case Study Tungesvik’s bland description fails to reflect the risks and uncertainties faced by those trying to put together offshore gas marketing plans in Brazil. If Equinor and its partners go forward with their plan to monetize that massive gas reserve, the result is likely to be a case study for those who follow. It could either be a model for successful development or a cautionary tale.