Innovative Approach to Managing High Wax Content in an Un-Piggable Deepwater Subsea Gas Pipeline

Atoll field is a high-pressure high-temperature subsea gas field located in the East Mediterranean at 930-meter water depth. The field is producing from the Oligocene layer, Contains a high condensate gas ratio of 29 STB/MMSCF with high wax content and WAT of 37°C. The objective is to manage wax deposition issues in this Atoll production system and hydrate formation in the 111 km pipeline. Wax deposition is managed by injecting continuous wax inhibitor through the umbilical, which decreases the WAT to around 18°C. A two-stage process for wax mitigation is proposed. The first stage involves a chemical soak using xylene and hexane. The second stage includes a pigging campaign. The team proposed a virtual pigging system using MEG injected from onshore to the well flowlines through the subsea umbilical, in addition to shut down wells to allow liquid redistribution in the pipeline. The wax precipitation leads to a production decrease of 1.0 MMSCFD without any change in well performance, meaning the field would reach zero production in less than one year without intervention. Once the wax precipitates at a certain distance (first 20 km section), it behaves like an orifice, causing additional JT cooling effect and leading to hydrate formation. This created a complex and challenging problem of wax and hydrate formation in the subsea pipeline system. Atoll pipeline experienced three full blockage events. The virtual pigging job was repeated many times, resulting in increased field production compared to the condition before the intervention. PHPC established field-operating guidelines that defined intervention triggers, outlined methodologies, and updated the hydrate management strategy to account for the JT cooling effect caused by wax buildup. These improvements significantly reduced the need for interventions from four times a year to potentially just once annually. This innovation delivered a total gain of 76.5 K MMSCFD of gas and over 1.86 million bbl of condensate between 2021 and 2024 compared to 2020. This pioneering innovation of virtual pigging using MEG through the umbilical in a subsea pipeline without pigging facilities offers a new approach to wax and hydrate management. The methodology provides valuable insights for similar subsea developments and contributes to improving flow assurance under extreme offshore conditions