Broad Strategy to Face with Complex Reservoirs: Expressive Results of Production in Pre-Salt Area, Offshore Brasil

摘要

Recently discovered oil fields in the Pre-salt area in the Santos Basin, offshore deepwater Brazil, containrna huge volume of hydrocarbons in carbonate rocks, mostly of microbial origin, with pronouncedrnheterogeneity, without any analogues in the world. The fluid usually presents expressive levels ofrncontaminants and a significant compositional grading, laterally and vertically. This complexity denotesrnhow challenging is to define robust development plans and suitable recovery mechanisms. In order tornadequately address these issues and optimize the hydrocarbon recovery, the development strategy wasrnsupported on three pillars: (i) extensive data acquisition; (ii) strong interpretative work on the geologicalrncharacteristics which impact fluids displacement and (iii) adoption of comprehensive recovery mechanismsrnand strategies, adequate for the various scenarios generated in the studies. The data acquisitionrnprogram includes, at first, a high resolution seismic data acquisition and interpretation. Well informationrncomprises conventional logs, image logs, cores, downhole fluid samples, sidewall cores, pressure transientrntests. Additionally, for each area candidate for a production system, an extended well test is performed,rnwith on-line interference tests with neighboring appraisal wells, aiming to evaluate the dynamic propertiesrnin terms of areal and vertical connectivity, as well as to anticipate potential problems regarding formationrndamage, fluid composition variation and flow assurance. Even with this comprehensive data acquisition,rnthe complexity of reservoir rock sustains a large range of uncertainty in their properties, which will onlyrnbe reduced throughout the productive life of the field. Therefore, the second pillar of the field developmentrnis built through a deep dive on the data by the geoscientists, in order to extract the geological attributesrnthat impact the displacement and sweep efficiency of the oil. This goal is not always possible to obtainrnin a straight and deterministic way, but often through multiple possible scenarios. This is referred mainlyrnto features as horizontal permeability distribution, presence of faults and barriers, vertical communication,rnfracture corridors, high permeability channels, among others. For the construction of the third pillar, arnstrong synergy between the disciplines of geoscience and reservoir engineering is necessary, so that therngeological interpretation is incorporated and applied to the flow simulation model and, the most important,rnsupport the design of robust strategies to optimize oil recovery, under uncertainty conditions. Whenrninformation is considered as perfect, it is immediately incorporated into the plan. Otherwise, multiplernscenarios will persist for a longer period, making it necessary to apply strategies that can be effective inrndifferent conditions, and can be matched as soon as the real scenario is revealed. This paper describes thernapproach adopted for the development of the Pre-salt fields, supported by the aforementioned three pillars,rnand details the main strategies to maximize oil recovery under uncertainty conditions, presenting somernresults from the operation of the first production systems.