SUBSEA SYSTEM ARCHITECTURE FOR CORAL SOUTH FLNG

Transcription

1 Introduction to Eni Our new mission: We are an energy company. We are working to build a future where everyone can access energy resources efficiently and sustainably. Our work is based on passion and innovation, on our unique strengths and skills, on the quality of our people and in recognizing that diversity across all aspects of our operations and organization is something to be cherished. We believe in the value of long term partnerships with the countries and communities where we operate. Highlights: Eni is active in 69 countries in the upstream sector the exploration, development and extraction of oil and natural gas. In particular, we are the world s number one in oil exploration; since 2004 we have discovered 11.9 billion barrels of resources, representing around 2.4 times our total production in the same period, when the industry average is 0.3. In 2015 Eni supplied 4.2 BSCM of feedgas to LNG plants, held 10.9 BSCM of liquefaction capacity, 15.6 BSCM of regasification capacity and sold 13.5 BSCM equivalent of LNG. Eni intends to significantly strengthen its position along the whole LNG chain. This growth will be largely driven by Mozambique where Eni is a significant player. Mozambique / Area 4 Eni entered Mozambique in December 2006, with the signature of the Exploration and Production Concession Contract (EPCC) for the Area 4 block in the Northern deep offshore area in the Rovuma Basin. The first discovery in the Area 4 block was made in October As of today, fourteen exploration and appraisal wells have been drilled. The wells have confirmed the huge gas discoveries of Area 4 at around 85 Tcf of gas in place, of which around 35 Tcf exclusively located in Area 4, the remaining straddling between Area 4 and the adjacent Area 1 block. The exploration success in Mozambique expands the leadership of Eni in Africa and opens a new Eastern front to its activities. Eni East Africa (71.43% Eni, 28.57% CNPC) is the operator of the Offshore Area 4 block with a 70% participating interest. Co-venturers in the Area 4 are Empresa Nacional de Hidrocarbonetos de Mozambique E.P. (ENH) (10%), Galp Energia Rovuma (10%) and Kogas Mozambique (10%). Coral South FLNG project involves the construction of 6 subsea wells connected to a floating production facility FLNG (Floating Liquefied Natural Gas), with a liquefaction capacity of over 3.3 million tons of liquefied natural gas (LNG) per year, equivalent to approximately 5 billion cubic meters. Mozambique authorities approved the project development plan in February

2 This project highlights Eni s technological leadership in the development of deepwater gas fields via FLNG facilities. The Coral field, discovered in May 2012 and outlined in 2013, is entirely located within Area 4 and contains about 450 billion cubic meters (16 TCF) of gas in place. In October 2016, Eni and its Area 4 partners signed an agreement with BP for the sale of the entire volumes of LNG produced by the FLNG Coral South, for a period of over twenty years. In November 2016 Eni's Board of Directors has authorized the investment for the first phase of the development of the Coral discovery (Coral South project), located in the deep waters of the Rovuma Basin (Area 4), offshore Mozambique. Coral South FLNG Subsea Eni has been one of the first oil Companies in developing Deep Water exploration and production technologies. Eni has acquired considerable know-how and has adopted state of the art technologies and methodologies in this sector installing XTs around the world at different level of water depths from shallow to deep. Subsea production facilities for Coral South FLNG project, illustrated in the figure below, will include 6 subsea wells, 3 production manifolds, 6 flexible flowlines, 6 flexible risers and 3 umbilical lines connecting the wellheads to the FLNG vessel. Figure 1 Coral South pictorial The subsea system architecture has been developed considering the operating philosophy and constraints of the whole field: 2

3 No bottlenecks in the subsea production system: the feed gas producible from the subsea wells can satisfy the maximum capacity of the liquefaction unit onboard the FLNG. Full subsea system redundancy, for maximising availability: the system is designed to guarantee the required feed gas rate even in case of shutdown of one cluster of two wells; Continuous MEG injection for hydrate prevention at the Xmas tree through the umbilicals, so to optimize the number of lines to be installed; Round-trip pigging capability from topside for flowline inspection and cleaning as might eventually be required; As the individual well productivity is substantially higher than the actual production rates required during most of the project life, the impact of planned or unplanned events on gas production and deliverability from individual wells or flowlines can be mitigated by increasing production from the unaffected wells. This provides a high level of operational flexibility not typically encountered in most upstream gas field developments associated with LNG projects. Coral South FLNG Seabed Figure 2 Area 4 subsea geophysics The predominant feature of the Coral development area is the Vamizi Canyon which crosses from west to east across Coral. The Vamizi Canyon is joined by the Metundo Canyon and the Nuini Canyon to the west of development resulting in a large canyon complex. Coral South is located on the 3

4 southern side of this canyon complex. Studies of the canyon itself have shown a complex geological composition of sand, gravel, clay and silt from historical spreading slides and flow events which have resulted in a very uneven canyon floor which has proven difficult to investigate due to the very heterogeneous geological composition. Evidences obtained through age dating showed that turbidite flow events through the canyon have taken place within the last 250 years hence the canyon is considered as potentially active for debris and turbidite flows. The potential size and strength of these flows have been assessed and an FLNG is considered the most prudent solution in de-risking the project of possible future geological events, since the whole Coral South FLNG development is out of the canyon boundaries. The geophysical and geotechnical campaign investigated the canyon area and focused on the development area. In order to add confidence in the subsea development, an extensive geophysical and geotechnical campaign has been implemented within the Rovuma Basin of North East Mozambique in the last five years. Being an unexplored area, at the beginning of the project there was very few data available with almost no geological information in the deep water areas. The first phase of the campaign was a detailed geophysical AUV campaign implemented in 2013 consisting of 2m x 2m bathymetry across the development area with side scan sonar, boomer and pinger. This information was reviewed in parallel with the survey and a shallow geotechnical campaign covering 6m below the seabed to enable an initial profile of the area and to validate the interpretation of the geophysical survey. Following this campaign and the first detailed geological model of the development area, a second more intensive campaign was implemented with a variety of investigation techniques including CPTs, piston cores, box cores and boreholes (up to 120m depth) for a total of about 250 sampling and testing. This was organised in parallel with the FEED for Coral South project to ensure that the data collected were relevant to the proposed design of the FLNG and to reduce uncertainty in the geological model and therefore to reduce project risks. The information were collected and used for geotechnical investigation for flowlines and foundations, slope stability analysis and geohazard review. With all the available data acquired, a ground model of the area has been created which enabled a detailed understanding of the processes that created the geology of the area and what processes are active today. At present, the site area is considered fully characterized allowing the project to be brought forward with confidence. Coral South FLNG Subsea facilities The subsea facilities are designed for up to 2,300 m water depth, with service life of 30 years and will generally comply with the following criteria: Use of well-proven, reliable technology, plus standard and qualified equipment; Modularity and interchangeability of components with other Area 4 projects; Flexibility of the system; and 4

5 Optimisation of the number and complexity of the subsea structures. As the availability of the facilities depends on maintainability aspects, equipment and components have been standardised to reduce maintenance costs and to increase the overall system reliability. The 6 subsea Xmas trees consider a horizontal 7 tree, with a pressure rating of 690 bara (10,000 psi). Figure 3 Xmas tree All the subsea wellhead trees will be provided with a multiphase wet gas flow meter (WGFM) upstream of the choke valve. As a back-up to the flow meters, pressure transducers upstream and downstream of the wellhead choke will also be used to monitor flow rates. All chemicals, including MEG, will be delivered to the XTs for the injection into production. The subsea facilities will include three production manifolds that are controlled from the FLNG vessel through umbilical lines. The manifolds have an arrangement that has been field proven in other applications. Each manifold will have two main headers to collect the individual well streams, allowing a range of operations like commingling gas wells in a single flowline or even switching the flowline. 5

6 Figure 4 Subsea manifold The manifolds are connected to the flexible risers located near the FLNG vessel through six flexible flowlines, with a total combined flowline length of approximately 21 km. The flexible risers will have two different sections, a bottom section that connects to the flowlines and a top segment that connects to the FLNG turret. The risers will have the same internal diameter as the flowlines. The umbilical system comprises the following main facilities: Topside termination unit providing the physical interface connection between the subsea umbilical network and the topside production control system equipment. Three umbilicals and ancillary equipment connecting the topside FLNG equipment and the subsea production system; Three subsea termination assemblies, including ROV operated isolation valves, hydraulic and electrical distributions, and couplers and connectors; The topside facilities associated with the SPCS will include the following components: Master Control Stations (MCS) to control and monitor the subsea and topside control systems and to interface with other FLNG systems; Uninterruptible Power Supply (UPS) unit to provide electrical power to the subsea equipment; Hydraulic Power Unit (HPU) to generate and provide hydraulic power to the subsea control system equipment at the required pressure levels; and Topside Umbilical Termination (TUTU) unit to provide the physical interface connections between the umbilical network and the topside SPCS equipment. The MCS will include the control and data processing units, the Human-Machine Interface (HMI) unit, and the subsea communication units. 6

7 CONCLUSION Coral South Development Project started in 2011 with the first gas discovery in Area 4. The interested area has been covered by extensive surveys which provided all the data required for the design of the subsea facilities and to minimise the relevant risks. The design of the subsea facilities has been carried out with the objective to avoid bottlenecks for the FLNG production in all the operating conditions and to have full redundancy in order to maximise the availability and production of the whole Project. 7