Initial Start-Up of India's First Deepwater Oil Field - Addressing Flow Assurance Challenges with Innovative Strategies

Abstract The M-field development plan involves an FPSO located in 400 meters of water, with five subsea oil wells connected through a 10-inch dual flowline system in a daisy chain configuration tied back to the FPSO using flexible risers. This paper describes the flow assurance challenges associated with the start-up of deepwater oil field in India, as well as presenting the novel approaches utilized to overcome these to ensure the successful commencement of oil production. Initial start-up strategy involves a phased approach to opening four wells, employing a gradual opening and well bean-up strategy over a period of 32-36 hours to achieve the desired ramped-up production rates. Transient simulations using OLGA model to predict flow behaviors in various field sections and address flow assurance challenges during the initial well start-up phase. Simulations identified a significant risk of slugging, characterized by cyclic zero-gas arrival at the FPSO. Additionally, the simulations indicated possibility of temperatures remaining below the treated pour point during the well bean-up process, which could lead to wax gelation within the network. Transient simulations were utilized to develop a flow assurance strategy to address challenges encountered during the start-up phase. It was deemed essential that mitigating slugging would not only guarantee uninterrupted operations at the FPSO but also reduce the likelihood of wax deposition. The primary objective of flow assurance is to uphold the design flow conditions from the onset of production, thereby keeping the subsea system temperature above the Wax Appearing Temperature (WAT). As part of the standard operating procedure, the circulation of hot diesel in the dual pipeline system through the FPSO is established to pre-heat the pipelines before initiating well start-up. Nevertheless, a significant challenge that remains unresolved is the occurrence of slugging during the ramp-up phase, leading to rapid cooling in the pipeline system. To address this issue and ensure the maintenance of design flow conditions from the outset, continuous circulation of hot diesel along with topside choke optimization at FPSO during the initial start-up phase until production reaches the desired level will not only alleviate slug flow condition but also eliminate low-temperature conditions in the subsea system. This approach will consequently reduce the propensity for wax deposition and promote a seamless commencement of operations. With implementation of this strategy, successful commencement of the oil production from the country's first deepwater field is achieved. The lessons learned during start-up operation are a combination of work-around, benchmarking of field data with predicted simulation results, and general operational experiences related to flow assurance.