Greater Tortue Ahmeyim LNG, the deepest offshore project in Africa

The latest Oct 2023: A contract has been awarded for the completion of the laying of subsea pipelines for the ultra-deepwater Greater Tortue Ahmeyim (GTA) natural gas project offshore Mauritania and Senegal.

The contract was awarded to Allseas by BP plc. It covers the installation of approximately 75 kilometres of two 16-inch export pipelines with field termination assemblies (FTAs) in water depths between 1,500 and 2,800 meters, and four 10-inch CRA infield lines with FTAs up to two kilometres long in 2,800 meters of water.

Allseas will reportedly undertake the GTA offshore pipelay works in early December using the world’s largest construction vessel, Pioneering Spirit. Installation support will be provided by the company’s offshore construction support vessel Oceanic.

An Overview of the Greater Tortue Ahmeyim LNG

Greater Tortue Ahmeyim is an offshore liquefied natural gas (LNG) project that is being developed on the maritime border of Mauritania and Senegal. The project is being developed by BP, Kosmos Energy, Societe des Petroles du Senegal (Petrosen), and Societe Mauritanienne des Hydrocarbures (SMHPM) with BP as the operator.

The project is based on the development of two offshore gas fields dubbed the Greater Tortue and Ahmeyim. The Greater Tortue field is located in the Saint Louis Offshore Profond block of Senegal. The Ahmeyim field on the other hand is located in the C-8 block in Mauritania’s offshore waters.

The C-8 block offshore Mauritania is 62% owned by BP, 28% by Kosmos Energy, and 10% by SMHPM. The Saint-Louis Offshore Profond block offshore Senegal is 60% owned by BP,30% by Kosmos Energy, and 10% by Petrosen.

Scope of the Greater Tortue Ahmeyim project 

The Greater Tortue Ahmeyim (GTA) LNG project is being implemented in phases. In the first phase, which commenced back in 2019, the GTA LNG project will be developed with a deepwater subsea production system comprising four gas production wells. The wells are tied back to a floating production, storage, and offloading (FPSO) unit.

The gas will be processed for the removal of heavier hydrocarbon components on the FPSO, after which it will be transported via a new 100km-subsea pipeline to a near-shore Floating Liquefied Natural Gas (FLNG) vessel dubbed Gimi.

The Gimi FLNG will be capable of producing 2.5Mtpa of LNG a year for global export while the remaining gas will be sent through pipelines to Mauritania and Senegal gas markets, for domestic consumption. This phase is expected to start commercial production in 2022 with a capacity of 2.5Mtpa of LNG.

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BP Gas Marketing will off-take the entire LNG output from the Greater Tortue Ahmeyim phase one development. The entire Greater Tortue Ahmeyim LNG project is expected to produce up to 10 million tonnes of LNG a year (Mtpa) when operational.

Greater Tortue Ahmeyim LNG Project Timeline

2015

Tortue 1 discovery well was drilled up to a total depth of 5,250m. Drilled by the Atwood Achiever drillship, the Tortue 1 well encountered 117m of net gas pay.

2016

The Ahmeyim-2 discovery well was drilled to a total depth of 5,200m. Guembeul-1 was also drilled in the same year. Ahmeyim-2 encountered 78m of net gas pay while the Guembeul-1 met 101m.

In December, BP entered into a partnership agreement with Kosmos Energy to co-develop the gas fields.

2017

In October, CH2M HILL was subcontracted by KBR for the civil and marine engineering services of the Greater Tortue Ahmeyim LNG project.

2018

In February, the government of Mauritania and of Senegal signed an inter-government cooperation agreement to develop the cross-border Greater Tortue Ahmeyim offshore gas field. Spread over 33,000km², the field is estimated to contain approximately 15 trillion cubic feet (tcf) of recoverable gas reserves.

In April, a front-end engineering and design (FEED) contract for the Greater Tortue Ahmeyim (GTA) LNG project’s FPSO was awarded to TechnipFMC.

In the same month, Eiffage Génie Civil Marine in a consortium with Saipem was awarded the FEED contract for the near-shore terminal of the project.

In October, KBR was awarded a FEED contract for facilities integration as well as for the terminal quarters and utility management for the near-shore terminal.

2019

In February, BP signed a 20-year lease and operation agreement (LOA) for the Greater Tortue Ahmeyim FLNG unit with Gimi MS Corporation. Estimated to cost US$ 1.3bn, the FLNG development involves the conversion of LNG carrier Gimi at Keppel Shipyard in Singapore.

GIMI MS will construct and operate the FLNG unit. It will invest 70% of its total development cost, while First FLNG, a subsidiary of Keppel Capital, will provide the remaining 30% of the FLNG development cost.

In the same month, Eiffage Génie Civil Marine and Saipem consortium were awarded the Engineering, Procurement, Construction, Installation, and Commissioning (EPCIC) contract for the near-shore terminal of the project.

In March, TechnipFMC was awarded the EPCIC of the FPSO unit.

In April, KBR was also awarded the pre-FEED contract for the second and third-phase development of the Greater Tortue Ahmeyim offshore project.

In May, KBR was awarded the Engineering, Procurement, and Construction Management (EPCM) contract for the facilities integration as well as for the terminal quarters and utility management for the near-shore terminal of the project.

May 2021

Greater Tortue Ahmeyim LNG Project phase one implementation 58% complete

The initial phase of the Greater Tortue Ahmeyim LNG Project is reportedly over 58% complete. This is seen in Kosmos Energy Ltd.’s financial and operating results for the first quarter of 2021.

According to the company, significant progress has been made on all major sites. This includes the floating production, storage, and offloading (FPSO) unit, the floating liquefied natural gas (FLNG) facility and the central terminal (concrete breakwater). It also includes a deepwater subsea production system that comprises four gas production wells.

The project execution activities commenced back in 2019 with the first gas expected in 2022. However, due to some unexpected interruptions like the wake of the COVID-19 pandemic at the beginning of last year, the first gas is expected in the first half of 2023.

How gas will be produced

Once operational, the Greater Tortue Ahmeyim project will produce gas from the ultra-deepwater subsea system and the mid-water FPSO vessel that will process the gas, removing heavier hydrocarbon components.

The gas will then be transferred to the FLNG facility at an innovative nearshore hub located on the Mauritania and Senegal maritime border. The FLNG facility is designed to provide circa 2.5 million tonnes of LNG per annum on average, with the total gas resources in the field estimated to be around 15 trillion cubic feet.

The project, which is the first major gas project to reach FID in the basin, is planned to provide LNG for global export as well as make gas available for domestic use in both Mauritania and Senegal.

August 2021

The sale and leaseback of Greater Tortue Ahmeyim LNG’s FPSO concluded

Kosmos Energy, one of the companies working on the Greater Tortue Ahmeyim (GTA) LNG Project, has announced that the transaction for the sale and leaseback of the GTA floating, production, storage, and offloading vessel (FPSO) that is currently being built by Technip Energies in China, has been successfully completed.

According to the FPSO Sale, Purchase, and Lease Agreement, the FPSO vessel has been sold to BP Plc a shareholder in the Greater Tortue Ahmeyim LNG Project.  BP as the buyer (BP Buyer), will lease the FPSO vessel to BP as the operator (BP Operator) under a long-term lease agreement, for exclusive use in the GTA LNG project.

Also Read: Greater Tortue Ahmeyim LNG Project phase one implementation 58% complete

BP Operator will continue to manage and supervise the construction contract of the FPSO vessel with Technip. The vessel is expected to be delivered to BP Buyer when its construction is complete, expectedly late Q3 2022.  The FPSO will enter into international waters at the same time and the lease will also become effective immediately.

Kosmos will compensate BP Operator for its contribution in cost under the lease agreement, which will be classified as an operating expense.

Significance of the sale to Kosmos

This transaction secures additional funding for Kosmos’ future development costs on the GTA LNG Project whose net capital expenditures in 2021 for Kosmos were estimated at around US$ 350M. These expenditures have now been reduced to approximately US$ 190M, with remaining cash calls on the project covered through the proceeds of the sale.

The balance of the sale proceeds, as well as the additional savings from the transfer of remaining FPSO construction payments to BP, are expected to be largely realized in 2022. The company (Kosmos) also announced that it expects to refinance National Oil Company loans later this year, providing approximately US$ 100M in additional financing for the GTA LNG project.

Progress on the Greater Tortue Ahmeyim (GTA) LNG Project

Furthermore, it revealed that work on the Greater Tortue Ahmeyim (GTA) LNG Project is going well. For the floating LNG vessel, four remaining sponsons have been integrated into the final dry dock, while the construction of the living quarters on the FPSO is complete.

Seven caissons have all been transported offshore three of them installed to form a breakwater, and all subsea trees have been built.

In mid-November, Kosmos Energy announced that the mechanical completion work had started for the floating LNG vessel, and the topside integration and hull and living quarters mechanical completion activities were also underway for the FPSO.

“Twelve of the caissons have been installed for the breakwater for the LNG jetty and fabrication has also begun on the 20th (penultimate) caisson,” said the company adding that, “Marine supply bases have been established at Nouakchott and Dakar to support subsea operations.”

Feb 2022

Construction of 21 concrete caissons as part of BP’s Greater Tortue Ahmeyim LNG project completed 

The African FLNG Project has now attained the construction of 21 concrete caissons; the works have been completed this month. This project is part of BP’s Greater Tortue Ahmeyim LNG project. The GTA project aims to make use of two natural gas reserves; Ahmeyim and Tortue. The reserves are spread over 33,000 km², with a combined amount of 15 trillion cubic feet of gas. 

The African FLNG Project is located on the maritime boundary of Senegal and Mauritania, approximately 110 kilometres from the city of St. Louis. This breakwater is considered vital because it will protect GTA’s key infrastructure- a floating LNG vessel, as well as utilities and accommodation platforms from the Atlantic Ocean, swells.

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Progress Thus Far

At a purpose-built site in Dakar, France’s Eiffage Civil Marine built all the caissons.

The structures have been towed to a deep-water holding site right off Goree Island. As of the first week of February, 16 of the caissons had already been installed offshore. Each of the caissons weighs well over 16,200 tonnes and measures 55 meters long, 28 meters in width, and 32 meters in height. The project’s construction called for the production of well over 130,000 cubic meters of concrete, 30, 000 tonnes of steel were also needed. 

Effiage revealed that the construction of The African FLNG Project’s activities involved about 1700 people, 97% being of Senegalese nationality. Effinger is now planning to build a gas transfer platform for the GTA. The first phase of the GTA scheme will involve deep-water subsea wells. These wells will be sending liquids and gas to a floating production, offloading, and storage unit moored on the continental shelf. Liquids will then be offloaded onto shuttle tankers, with the gas piped to Golar LNG’s 2.5 million tonnes per annum floating liquefaction unit for subsequent export(s).

Jan 2023

Greater Tortue Ahmeyim’s FPSO vessel begins its journey to the site

The floating production, storage, and offloading (FPSO) vessel for the Greater Tortue Ahmeyim FLNG project has started its journey toward the project site off the coasts of Mauritania and Senegal. This comes after approximately three and half years of construction and a series of sea trials in Qidong, China.

The FPSO will cover a distance of approximately 12,000 nautical miles, the equivalent of 22,224 km, between the quay of the construction shipyard in China and the production perimeter.

The arrival date has not been announced. However, according to projections, it should arrive in time for the commissioning of the Greater Tortue Ahmeyim FLNG project. The commissioning was announced for the third quarter of 2023.

Aug 2023

Tortue Ahmeyim’s Golar Gimi FLNG unit to sail to site in Sep 2023

Tortue Ahmeyim’s Golar Gimi FLNG unit is set to sail to site September 2023. This is according to Golar LNG, the company tasked with delivering the unit.

Golar LNG said that currently, the FLNG Gimi conversion works are 97% complete adding that, “the final checks, storing up and sea trials will take place in Singapore starting around the end of September/early October.”

According to reports the construction of FLNG Gimi has cost upwards of US$ 1.3bn.