Bijupira Salema: Flow Assurance Analysis to Support Operating Strategy

Abstract

Abstract This paper highlights the flow assurance analysis performed to develop operational strategies for the Bijupira and Salema deepwater development offshore Brazil. Benchmarking the thermal performance with data from the initial field start-up is presented. Operating strategies were developed for shutdown, restart and remediation options through detailed flow assurance modeling. One of the major operational challenges for the Salema field is the inability to depressurize the downhill flow lines. To protect the Salema flow lines from hydrate formation, the flow lines would require dead oil displacement even for short-term shutdowns. A novel method of depressurizing was identified and modeled by opening the pigging valve subsea and then depressurizing one flow line in the roundtrip loop. This method enables the operator to reduce the deepwater flow line pressure quickly to avoid hydrate formation after a shut down, thereby reducing downtime and lowering the risk compared to the conventional method of flow line displacement with dead crude. Various schemes of hot oil circulation were also investigated to avoid the need for injecting large volumes of hydrate inhibitor during well start-up. This procedure has already been implemented in the field start-up operations, which has resulted in savings in operating costs. Based on the flow assurance modeling results, operational strategies were developed for the two scenarios - process upsets, which can be rectified within the system cool down time and secondly for prolonged shutdowns requiring treatment of wells, flow lines, and risers. Benchmarking thermal performance of the subsea production system with data from the initial field start-up has assisted the operator to optimize the operations. Introduction Bijupira & Salema field is located in the Campos Basin offshore Brazil. The two fields are developed as subsea tiebacks to an FPSO with offset distances ranging from 2 to 3 km. The system comprises subsea manifolds, flowlines and risers with capability for round trip pigging. A previous paper highlighted many of the flow assurance challenges in this field1. The key flow assurance challenges include hydrate management, wax management, optimizing system deliverability with downhole gas lift, subsea chemical injection and liquid slugging. Field experience by Petrobras indicates that some of the subsea manifolds in the Albacora field were plugged with hydrates during a shut down event. This paper will present an overview of the flow assurance challenges and design solutions to manage hydrates and wax deposition in the subsea production system. Prior to the start-up of the field, several hydrate management challenges were identified. Hot oil circulation prior to start-up needed to be optimized to reduce the risk of hydrates while minimizing the consumption of chemicals. Salema field could not be blown down below the hydrate formation pressure after an unplanned shut down. Further flow assurance analysis was performed to develop the operating strategy specifically to address hydrate management philosophy. These analyses and operating strategies are presented in this paper. System Overview Bijupira and Salema fields are located in the Campos basin offshore Brazil located approximately 250 km East of Rio de Janeiro. The fields are being produced by the FPSO Fluminense, which has a processing capacity of 70,000 STB/day of oil, 75 MMSCFD of gas and water injection of 92,000 BPD. The FPSO has a storage capacity of 1.2 million barrels.