Offshore deepwater oilfield development
The Sangomar (formerly SNE Deepwater) oil field is located in the Rufisque, Sangomar and Sangomar Deep Blocks, which cover a combined area of 7,490km² within the Senegalese portion of the Mauritania-Senegal-Guinea Bissau Basin. The field was one of the world’s largest oilfields in 2014.
The project is being developed by a joint venture of Rufisque Offshore, Sangomar Offshore and Sangomar Deep Offshore (RSSD), comprising Capricorn Senegal, a subsidiary of Crain Energy (36.44%), Woodside Energy (31.89%), FAR (13.67%) and PETROSEN (18%), where Woodside Energy is the project operator.
The environmental and social impact assessment (ESIA) for phase one of SNE project was completed in November 2018.
The project owners submitted the development and exploitation plan to the Senegalese Government in October 2018. FEED activities began in December 2018 following the approval by the Senegalese Minister of Petroleum and Energies. The field was renamed Sangomar in November 2019.
Final investment decision (FID) for the project was achieved in January 2020. Work on the field development began in early 2020, while first oil from the project is anticipated to flow in 2023.
Production from phase one is expected to be approximately 231 million barrels (MMbbl) of oil. The total recoverable oil resources are estimated to be around 500MMbbl over the life of the field.
The Sangomar oil field was discovered in November 2014 with the drilling of the SNE-1 exploration well to a water depth of approximately 1,100m and a total depth of 3,000m. The well encountered a 95m gross oil-bearing column within upper Albian sandstones.
The oil field was further evaluated by drilling the SNE-2, SNE-3, SNE-4 and BEL-1 appraisal wells from November 2015 to May 2016.
The drilling and evaluation of the SNE-2 well was completed in January 2016. The well was drilled at a water depth of 1,200m and to a total depth of 2,800m within the Sangomar Block. Oil from the well flowed at 8,000bopd from the lower reservoir unit and at 1,000bopd from the shallower heterolithic reservoir unit during drill-stem testing (DST).
The drilling of the SNE-3 well was completed in March 2016. Oil from the well flowed at a maximum rate of 5,200bopd and had a main flow rate of 4,500bopd over a six-hour period during DST.
Completed in April 2016, the BEL-2 well encountered an oil column of 100m and confirmed the extension of reservoirs in the northern area of the oilfield.
The SNE-4 was drilled at a water depth of 942m and to a total depth of 2,944m within the Sangomar Block in May 2016. It encountered a gross oil column of 100m in the upper reservoir and confirmed the extension of reservoirs in the eastern extent of the oilfield.
As of August 2017, the contingent recoverable resources from the field were estimated to be 1C, 2C and 3C of 346 million metric barrels (MMbbl), 563MMbbl, and 998MMbbl respectively.
Phase one of the development project, the Sangomar field development phase 1, will feature a permanently moored floating production storage and offloading (FPSO) facility along with 23 oil production wells and associated subsea systems.
With a length ranging between 250m and 325m, the FPSO will be installed at a water depth of 800m. The FPSO will also hold the tie-backs of the oil production wells, along with water injection and gas interjection wells.
The oil storage tank of the FPSO unit will have a capacity to hold one million barrels of processed oil. The FPSO will allow the integration of subsequent development phases, including gas export to shore and future subsea tie-backs from other reservoirs and fields.
The subsea system will comprise wellheads and subsea trees, 9km to 22km in-line tees, up to six manifolds, flowlines and risers ranging from 50km to 150km (connecting to the FPSO), 15km to 50km of flowline end terminals, and 15km to 70km of umbilicals for the monitoring of wells.
The exploration wells were drilled with Transocean’s fifth-generation, dynamically positioned, semi-submersible deepwater drilling rig named Cajun Express.
The appraisal wells were drilled using the seventh-generation dual-activity drillship named Ocean Rig Athena.
A subsidiary of Japan-based MODEC, MODEC International, was awarded the front-end engineering and design (FEED) contract by Woodside Energy for the FPSO unit of the SNE project in February 2019.
A joint venture between OneSubsea, Schlumberger and Subsea 7, Subsea Integration Alliance, was awarded the FEED contract by Woodside Energy in December 2018 for the subsea infrastructures, comprising subsea umbilicals, risers and flowline systems (SURF).
The Senegalese Ministry of Petroleum and Energies awarded the advisory contract to Doris Engineering for the project in January 2019.
An environmental and social impact assessment (ESIA) for the offshore development project was conducted by Earth Systems and Xodus Group.
Transocean provided the drilling rigs for exploration and appraisal activities for the SNE project.
Diamond Offshore was awarded two well-based contracts for the Ocean BlackRhino and Ocean BlackHawk drill rigs.
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