General summary of Gas Compression, Dehydration, Injection Flowline De-Watering and Sweetening Systems typically found on Floating Production Storage and Offloading (FPSO).
Gas Compression and Dehydration
- Gas Dehydration should be based on a Triethylene glycol (TEG) system to remove water from the natural gas stream.
- Turbine drivers should be capable of handling the range of fuel gas compositions (including carbon dioxide content) and should be designed to automatically adjust to swings in fuel gas composition as wells are brought on and offline.
- Gas compression and dehydration facilities should be capable of operating on the full range of imported gas compositions at a capacity consistent with the functional requirement for provision of lift gas to start oil production.
- Reciprocating gas compressors should not be used.
Gas Injection Flowline De-Watering
- Provision should be allowed for temporary routing of the gas injection flowline to either the flare or the separation train to accommodate gas injection flowline dewatering during commissioning.
- Provision should be allowed for temporary routing of the gas injection flowline to the production flowlines to accommodate production flowline de-watering during commissioning.
- Dewatering should be carried out within the liquid handling constraints set by the topsides. Low temperature issues should be managed appropriately, if necessary via inclusion of temporary topsides equipment.
Gas Sweetening System
- FPSO including turret piping and equipment downstream of the gas sweetening unit should be robust to failure of the gas sweetening unit, taken to be none of H2S is removed from the processed gas, coincident with failure of the gas dehydration. This provides design robustness against an unrevealed failure of the gas sweetening unit and dehydration system to meet specification (from a hydrogen induced cracking / sulphide stress cracking perspective).
- In order to manage subsea flowline and downstream equipment integrity (including wells) the gas sweetening unit should be configured such that the risk of the H2S concentration exceeding, assuming, 100 ppm (volume basis) meets Layers of Protection Analysis (LOPA) requirements.
- Allowance should be made for future gas export such that the gas sweetening system can be re-configured with the FPSO on station to achieve an H2S content of predetermined value "ppm" (maximum, volume basis) and an inert gas content (CO2, N2) content of predetermined value "mol%". The modification of the gas sweetening system must be executed as part of overall modifications to support future gas export.