Some new pre-salt fields at Santos Basin in Brazil are located in water depths as deep as 2200m and about 300 km away from the coast. There is variable level of contaminants in the produced fluid, mainly CO2 that affects the material selection of the infield flowlines and risers. Based on these constraints, Petrobras has selected UNS N06625 clad or lined steel linepipes to develop the first fields in Pre-Salt area and also the module 3 of Roncador a post-salt field in Campos Basin. Several challenges have arisen during design, construction and installation of these facilities related to pipeline welding procedures, NDT inspection and Engineering Critical Assessment (ECA). Firstly weld overmatching condition may not be fully achieved due to differences in mechanical properties between UNS 06625 and API X65, and concern increases when reel-lay installation method is chosen. Another welding issue is the maximum interpass temperature of nickel alloys (DNV and PETROBRAS standards limit that to 100°C) and this impacts pipeline installation productivity. Thirdly, back purging characteristics and number of passes protected with purging gases affects the possibility of root oxidation. Also, the inspection of the weld overlay in the pipe end of lined linepipes is other point of great concern. As defect sizing is mandatory for ECA, lined pipes have been designed with a weld overlay length which allows the inspection of the final girth weld by AUT. However, AUT solutions are normally more efficient in rolled or extruded materials than in weld overlaid ones. Additionally, the ECA methodology for both girth welds and weld overlay has complexities that are not usually addressed in a regular ECA for carbon steel pipelines (e.g. internal misalignment of girth welds in risers has stringent requirements because of its effects on fatigue performance and, consequently, the ECA girth weld criteria). Also CRA clad/lined pipelines and risers qualification program may include additional testing when compared with usual carbon steel welding qualification process (namely pitting and intergranular corrosion, full scale fatigue, spooling trials of lined linepipes, segment testing for ECA, and others). Finally, the contribution of clad/lined layer in pipeline design strength is also discussed. This work presents challenges PETROBRAS has faced at design and construction phases of on-going Guaré and Lula-NE pre-salt fields and Roncador field projects, as well as the solutions proposed by the project team in order to overcome the issues raised during project execution.
This paper describes different alternatives to be adopted to assess the integrity of weld overlays of flexible joints and lined pipes in offshore pipeline and riser projects. Protective layers are adopted as an interesting alternative to full thickness corrosion resistant alloys due to the possibility to adopt carbon steel as base material in order to reduce overall material costs. UNS N06625 (alloy 625) is generally selected for internal layers, such as weld overlay steels, lined pipes or clad pipes because of its sulfide stress cracking (SSC) resistance and outstanding weldability. However, unless the long-term integrity of the cladding or overlay as a protective layer can be demonstrated under the intended service conditions, the base material shall also be resistant against sulfide stress corrosion cracking. Due to low resistance of carbon steel to corrosion fatigue in the presence of contaminants in fluid content, the rupture of thickness of CRA (Corrosion Resistant Alloy) layer becomes a failure mode. An Engineering Critical Assessment (ECA) shall be performed in order to assess if circumferential planar flaws in weld overlay regions will not propagate through the CRA layer, thus exposing the base material, when submitted to critical cyclic loads during the service life. Such analysis would involve fatigue crack growth simulation and surface interaction of full circumferential embedded defects to determine the maximum weld overlay pass height to be limited by machining. This limited height of machined layers should guarantee that a full circumferential flaw will withstand the operational fatigue life. However, this is a very time consuming manufacturing process and would implicate additional concerns for long extensions due to out of straightness and out of roundness. Alternatively, the ECA results may be used to determine the flaw acceptance criteria and required probability of detection of volumetric non-destructive testing. Recent developments in ultrasonic inspection were successfully adopted and represent a better solution for alloy 625 weld overlay in terms of project scheduling and manufacturing costs. Radiographic testing may also be used provided it meets the required sensitivity, in terms of image quality indicators (IQI). Anyway, validation tests shall be performed to demonstrate adequate reliability to detect the minimum required flaw height.
This paper presents the technical solutions adopted and implemented to develop the Brazilian pre-salt reservoirs, covering the main aspects of the subsea production systems already installed and in operation, that allowed overcome the challenges and turn the ultra deepwater pre-salt production into a reality that currently produces more than seven hundred thousand barrels per day. The characteristics related to this particular ultra deepwater scenario are presented, highlighting the ones that demanded to push the envelope of the available technological solutions, considering the conditions are more severe than typical ones from the previous experience with Campos Basin development projects: presence of CO2 and H2S contaminants in the produced fluids; higher internal pressure; high CO2 content gas injection; deeper waters and more severe metocean conditions. The aspects related to subsea trees, control systems, subsea manifolds, diverless connection systems, subsea flowlines, umbilicals and risers for the production systems are presented, as well as the flow assurance issues. The risers and pipelines for produced gas flow to shore are also covered. Considering the large number of projects that would be required to develop the Brazilian pre-salt province, different riser system solutions were developed and applied, being now field proven and available for the industry. Several firsts and records were established and are presented. The effort related to subsea equipment standardization, to cope with the large number of systems to be installed, is also part of this paper. Similarly to the situation of Campos Basin in the 80's, playing the role of a big laboratory for technology development towards deep water production, Brazilian pre-salt scenario, and specially Santos Basin pre-salt province, is nowadays the site where technology development is taking place for ultra deepwater production of high GOR oil with variable CO2 content. Subsea systems are enabling such production and this technology enhancement will contribute for the future development of other areas with similar characteristics.
This paper aims to describe developments in the Santos Basin Pre-Salt risers systems, which in some few years experienced many different concepts to overcome big challenges. This paper also describes initiatives to optimize configurations with evolution and maturity of riser technologies and expectations for future developments. In Santos basin Pre-Salt cluster, due to the challenging environmental conditions, presence of H2S and CO2, water depth up to 2310m, production riser's insulation requirements, relatively high temperature and high pressure, the riser system design for this scenario was something innovative and challenging for the industry. Currently, due to lower oil prices, an even more complex scenario is in evidence, imposing even greater challenges for risers systems regarding cost reduction. The experience acquired with the implementation of the first projects was a key factor to find viable and comprehensive ways to optimize cost. In approximately 7 years of production in the Santos basin Pre-Salt layer, oil production surpassed 1 million bpd by using several different riser concepts: BSRs (Buoy-Supported Risers), SLWRs (Steel Lazy Wave Risers), Flexible Lazy Wave Risers, Free Hanging Flexible Risers and FSHRs (Free Standing Hybrid Risers). Nowadays, with greater maturity and new design premises, considerable cost reduction results have been obtained, mainly motivated by the reduction of buoyancy modules and reduction of riser sections quantity in the flexible risers. For the future, there are other ongoing optimizations studies to apply both flexible and rigid risers in free hanging configuration. In early stages of project development, an extensive engineering work on riser analysis, the establishment of new design premise and some changes on current design process were done through a joint effort by operator, partners and suppliers. These are key factors for the achievement of considerable cost reduction. The maturity reached with the riser system designs was obtained through several design cycles, whose process can bring more future cost reductions.
Offshore oil development projects are complex and require high capital investment. The application of methodologies that seek optimization of economic parameters of projects became particularly important since 2014, when oil barrel prices plummeted. At that moment, some projects required modifications to regain economical attractivity. The recovery of project profitability depended on the break-even oil price criterion fulfillment (typically USD 40-45) among other requirements. This paper presents a methodology developed by Petrobras to increase the profitability of offshore projects in conceptual design phase while meeting the technical and safety minimum requirements. Successful solutions provided by the Petrobras team, enabled through this methodology, to make more than 15 projects economically viable are presented. The solutions include phased development, reuse of flexible lines from declining production wells, application of new technologies (including boosting and processing), use of innovative subsea architectures, procedures to increase ramp-up speed, long tie-backs, etc. This article is focused on subsea engineering solutions.
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