A Perspective View of Flow Assurance in Deepwater Fields in Brazil

Abstract

Abstract Significant part of the Brazilian oil reserves is located in ultradeepwater fields (WD > 1500 m). In this scenario, flow assurance plays a crucial role due to the existing high pressures and low temperatures. This paper focuses on the strategies concerning flow assurance issues for the near future. These strategies are strongly based on our specific field experiences as well as on the foreseeable technological scenario. The future, as treated in this work, refers to the short and mid-term future and not to the prospective long term one. Thus, it will mainly discuss current R&D in flow assurance activities to tackle existing problems and the ones foreseen for the discoveries already in development. In order to facilitate the understanding of our vision, a brief summary about todays flow assurance issues is presented. Currently, the main flow assurance concerns are related to hydrate formation and wax deposition. Accordingly, design criteria and operational procedures to avoid these problems are briefly described. There is also an increasing concern about heavy and extraheavy oil production, since a relevant part of recent offshore discoveries involves this type of oil. Among the initiatives that are being taken aiming at optimizing flow assurance design in the near future, one can mention:rheology of heavy oil and water in oil emulsion;heavy oil multiphase flow (gas-liquid) simulation;hydrate slurry transportability;improvements on wax deposition modeling; andimprovements on heat management. Introduction Flow Assurance has been a relevant theme to field development teams in Brazil, since the mid 80's, with the discovery of Albacora and Marlim fields, both in deepwater. The pilot production systems for these fields were based on the use of Floating Production Units (FPU), subsea wells, flexible flowlines, gas lift as artificial lift method, and waterflood as the Enhanced Oil Recovery Method (EOR) (Figure 1). Due to high heat losses in multiphase flow, the wax deposition in the flowlines was severe, especially in Albacora, becoming, at that time, the main challenge to overcome. The application of corrective techniques, especially Nitrogen Generating System (SGN), an exothermal chemical reaction method to dissolve wax deposits, and round-trip cleaning pigs, has been decisive for the operational continuity of these pilot production systems(1). Nevertheless, cost-benefit analyses showed that preventive solutions would present a better economic result for the following development phases of these fields, as well as for other new deepwater fields. Such analyses also took into account the potential of hydrate issues in the multiphase flowlines. Therefore, more strict design criteria regarding flow assurance were adopted since then. Currently, the main flow assurance issues are still wax deposition and hydrate blockage. Accordingly, for steady-state condition, keeping the wellstream temperature above the wax appearance temperature (WAT) and outside the hydrate equilibrium envelope became a demand. This is accomplished by an appropriate subsea layout combined with insulated flowlines. Even if the wellstream temperature is designed to stay above the WAT, flowlines are usually designed to be piggable.