The Sanha Lean Gas Connection (SLGC) project is an offshore subsea gas pipeline system located at a water depth of 230ft, stretching from offshore Angola. The blocks are located in two different concessioons.
Developed by Chevron’s Angolan subsidiary Cabinda Gulf Oil Company (CABGOC), the project aims to deliver up to 480 million metric standard cubic feet of lean gas per day (scfd) from Sanha field, offshore Cabinda, Angola, to Angola LNG (ALNG) in order to mitigate a forecasted gas supply shortfall between 2022 and 2025.
Chevron holds a 36.4% interest in ALNG, which operates a single train onshore natural gas liquefaction plant located 350km north of Luanda in Soyo, Angola, with a processing capacity of 1.1 billion cubic feet of natural gas per day and liquefied natural gas (LNG) production capacity of 5.2 million tonnes per annum (Mtpa). Other stakeholders in ALNG include Sonangol (22.8%), BP (13.6%), TotalEnergies (13.6%), and Eni (13.6%).
The final investment decision (FID) for the SLGC project was taken in January 2021.
Sanha Lean Gas Connection (SLGC) project development details
The brownfield project includes the development of a lean gas platform, and SLGC pipelines.
The existing platforms at the Sanha condensate complex, which is located directly above the Sanha field, will undergo process, instrumentation, electrical and structural changes to enable connection with the new SLGC lean gas platform under the brownfield modification works.
The new SLGC’s lean gas platform is being developed as a fixed-legged, four-piled platform that will be connected to the Sanha condensate complex through a bridge. The platform will weigh 4,200t including the piles, bridge, and 285ft flare system.
Equipped with an electric booster compression module (BCM), it will have the capacity to process up to 600MMscfd of gas. The BCM will have two 6,000hp electric motor-driven compressors. Equipped with variable frequency drives, the compressors will increase the pressure of the gas to 3,300 pounds per square inch gauge (psig) when the reservoir depletes. The platform will maintain the pressure ideal for the pipeline that feeds the Angola LNG facility.
Two 20in gas pipelines and a 16in gas pipeline, measuring approximately 1.2km long each, will form the SLGC pipeline network.
The new connecting pipelines will tie the existing complex to the new SLGC lean gas platform for gathering and exporting gas from to ALNG via the existing Congo River Crossing subsea pipeline system. The subsea infrastructure of the SLGC will comprise a new riser and associated riser clamps for connecting the subsea pipeline to the Sanha Complex.
The project is expected to provide additional structural capacity to assist future booster compression for additional developments in blocks 0 and 14.
Existing Sanha condensate complex details
The Sanha condensate complex is located in Block 0, 48.28km offshore the Malongo terminal in Cabinda province, off the coast of Angola. The complex comprises a drilling production platform (DPP), a process and compression platform (PCP), and a quarters platform.
The DPP platform has 40 well slots and two rigs in operation for primary oil and gas separation, while the PCP platform has a turbo-expander liquified petroleum gas (LPG) plant for condensate stabilisation. The quarters platform has safe utilities and provides accommodation for 180 individuals.
The PCP platform receives oil and gas from the DPP platform wells as well as from other satellite fields. Oil and gas are processed into four product streams: LPG for export to floating production storage and offloading (FPSO) Sanha; treated gas that is reinjected into the Sanha reservoir; fuel gas for its own consumption and export to South Sanha and FPSO Sanha; and crude and condensate for export. The Sanha field achieved the first condensate production in March 2005.
EDG, a global consulting company, is responsible for the gas pressure reduction and flare capacity expansion of the project. The contractual scope includes front-end engineering design , and detailed engineering of the lean gas platform, flare system, bridge, and the BCM.
EDG contracted Cronus Technology, a consulting firm based in the US, to provide project management and engineering assistance for the pre-FEED design of the SLGC pipeline.
Subsea 7, a subsea engineering, construction and services company, was awarded the contract for the construction and installation of the lean gas platform system in January 2021.