Carbonate reservoirs contain expressive part of the world oil reserves. The exploitation of these resources, however, presents several challenges mainly associated with their complex pore geometry, large scale variation in permeability and sometimes unfavorable wettability. These challenges can become more significant when we move to a deep offshore environment. As off-shore projects need to be planned well in advance, due to the lack of room in the platforms for future expansion, the pioneer application of EOR methods needs to be considered from the conceptual stage of the development.
This paper addresses the approach used to design the development basis for Lula field, formerly known as Tupi area, in the Pre-Salt Cluster (SBPSC) in Santos Basin, offshore Brazil. It focuses on the strategy of phased development, dynamic data acquisition and actions to add flexibility to the production system and how to manage uncertainties. A comprehensive analysis of the existing uncertainties, such as the reservoir characterization, early water and gas breakthrough, bypassed oil saturation, flow assurance in deep water flowlines and CaCO3 scale possibility in production wells, favored a phased development concept aiming to mitigate risks. The approach used to cope with these uncertainties in a Pilot Project as well as in the future development scenarios is presented. Most of the discussion is focused on how to consider feasible Enhanced Oil Recovery techniques through Pilot testing and future implementation in large scale in the field. It comprises the investigation of different recovery processes and first field results, including miscible processes using hydrocarbon gas and CO2. To optimize the oil displacement, a water alternating gas (WAG) injection process is also being designed.
After one and a half year of extended well test production and the implementation of the first Pilot project in January, 2011, results confirm the decision of providing additional flexibility to the project. Dynamic appraisal proved essential to assess reservoir connectivity, evaluate stimulation methods, support reservoir characterization studies and define aspects related to flow in subsea lines. The first results of the injection of the CO2 stream, separated from the associated gas in the Pilot project, indicate that the chosen strategy has potential to be a successful one. The continuing production and pressure data monitoring of the WAG implementation in the Pilot, from 2012 on, will provide a more definitive conclusion about the feasibility. Good responses will translate in the EOR expansion to field scale.