In the early 2000s the context of the pre-salt formations was conceptual geological models of possible oil bearing reservoirs underneath a thick salt layer, many technical challenges, uncertainties and risks. Past only eight years from first discovery (2006), there are nine production systems, FPSOs, in operation, reaching an average oil rate of more than 700 thousand barrels per day and a cumulative production greater than 400 million barrels of oil, through 34 production wells. To optimize recovery, the first desulfated sea water and gas injectors were started. But these impressive numbers cannot be taken from granted: although nature has revealed prolific reservoirs, much experience, talent, planning and perseverance were necessary. The first articles addressing the pre-salt fields had a focus on the technical challenges faced on first years: the heterogeneous nature of the microbial carbonate reservoir, the 2,000 m salt layer and drilling concerns associated, the variable CO2 content and compositional grading in the reservoir fluids, flow assurance issues and special demands concerning subsea engineering, well construction and processing plant. The main drivers and development strategies were also established: staged development, based on extended well tests (EWTs), multi well production pilots and definitive systems prioritizing the standardization of well projects and production systems. Now, challenges and plans are rewarding the efforts, as depicted by the concrete production numbers achieved to date. In this text, a historical perspective of the pre-salt exploration and development is presented, emphasizing the previous unknowns and uncertainties and how they were treated in order to attain the results. As we still have a lot to learn, since we are just on the beginning of the development of this extraordinary petroleum province, a look to the future and the present efforts on optimization are also commented.
Since the beginning of the Santos basin pre-salt commercial production, in December 2010, more than 1 billion barrels of high quality oil have been extracted from these ultra-deep water carbonate reservoirs. To enable and accelerate production, Petrobras and its partners applied advanced and innovative technologies in various areas of engineering. This paper focuses on the reservoir strategies conceived during the design phase of the Lula and Sapinhoá development projects and their application in these fields. The authors highlight practices and processes whose extensive use, in this type of scenario, were not standard. Among these, the dynamic characterization of the reservoirs by the use of long-term tests coupled with remote monitoring of pressure; water and gas production control by alternating injected fluids; intensive use of intelligent completion; convertible wells to accelerate production growth (ramp-up); CO2 injection from the start of production; rock-fluid interaction tests; optimization of well stimulation and many others. Knowledge acquired during the first seven years of commercial production and the actions implemented to manage the reservoirs reflect on the production plateau extension and the final length of their expected productive life. The collection and analysis of static and dynamic data proved to be valuable to reduce uncertainties and support further development decisions. Integrated effort contributed to risk mitigation, production maintenance and increased forecasted final recovery. The results obtained emphasize the importance of an effective reservoir management approach to maximize production and recovery. Concepts adopted are clarified through practical examples showing the advantages and gains from their implementation. The final message is that safe and viable operation of ultra-deep offshore fields benefits from additional investments in acquiring specific reservoir data. Their integrated analysis using advanced and up-to-date techniques is considered essential to maintain and improve asset values.
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