Civil Engineering September 2022 | Vol 30 No 8

52 September 2022 Civil Engineering MOSSEL BAY OFFSHORE AND ONSHORE Subsea pipelines from the FA Platform to the GTL Refinery onshore Two subsea pipelines with a length of 87 km and diameters of 18 inch and 8 inch, which run from the FA Platform to the shore crossing, were installed in 1990. The 18-inch pipeline was installed to convey gas to shore with the 8-inch pipe- line designed for condensate (a mixture of liquid hydrocarbons). These sub-sea pipelines are tied into lines that run from the shore crossing to the GTL Refinery, over a distance of 6 km. The owner and operator of these pipelines is PetroSA. The gas pipeline was inspected in 2017 and the conden- sate pipeline in 2020. The UPRD Bill specifies that the pipelines, umbilicals and wellheads must be decommissioned and removed from the site. Effluent pipeline from the GTL Refinery out to sea An effluent pipeline, measuring 5 km in length and 14 inch in diameter, was installed from the GTL Refinery through the beach crossing and 1 km into the sea at Vleesbaai. The operator is PetroSA. Subsea pipelines and umbilicals – FA satellites development The FA Platform relied on a number of gas discoveries to supply gas to the GTL Refinery. It started with the FA satellites, where drilling for hydrocarbons com- menced and pipelines and umbilicals were installed. The FA satellites have been depleted and are no longer in use. Subsea pipelines and umbilicals – EM development The lease acreage where the EM develop- ment occurred belonged to PetroSA. PetroSA was the operator and installed the control buoy, well heads, pipelines and umbilicals to the FA Platform in 2000. After depletion of the gas the EM develop- ment was decommissioned and closed. Subsea pipelines and umbilicals – South Coast Gas The lease acreage where the South Coast Gas development took place belonged to Pioneer Natural Resources and PetroSA. PetroSA was the operator and installed the well heads, pipelines and umbilicals to the FA Platform in 2004. Pioneer Natural Resources transferred its lease to PetroSA and pulled out of South Africa. After deple- tion of the gas, the South Coast gas develop- ment was decommissioned and closed. Subsea pipelines and umbilicals – Ikwezi Development The wells are based off the F-O field lo- cated 40 km south-east of the F-A produc- tion platform. The pipelines are 12 inches with umbilicals to various wells and skids. First gas was achieved in 2014. The results of geological assessments of well reserves were underestimated (25 bcf instead of 242 bcf) and the project and did not deliver the intended results. The project has come to the end of its life. Onshore and offshore pipelines to the SBM A pipeline was installed from the PetroSA refinery to a tank farm at Vleesbaai. From the storage tank farm at the beach a multi- purpose bidirectional pipeline was installed Figure 6 Horizontal drilling through the surf zone for pipeline installation Figure 7 Offshore developments to the west of the FA Platform Figure 8 Offshore developments to the east of the FA Platform