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

Abstract

Recently discovered oil fields in the Pre-salt area in the Santos Basin, offshore deepwater Brazil, contain a huge volume of hydrocarbons in carbonate rocks, mostly of microbial origin, with pronounced heterogeneity, without any analogues in the world. The fluid usually presents expressive levels of contaminants and a significant compositional grading, laterally and vertically. This complexity denotes how challenging is to define robust development plans and suitable recovery mechanisms. In order to adequately address these issues and optimize the hydrocarbon recovery, the development strategy was supported on three pillars: (i) extensive data acquisition; (ii) strong interpretative work on the geological characteristics which impact fluids displacement and (iii) adoption of comprehensive recovery mechanisms and strategies, adequate for the various scenarios generated in the studies. The data acquisition program includes, at first, a high resolution seismic data acquisition and interpretation. Well information comprises conventional logs, image logs, cores, downhole fluid samples, sidewall cores, pressure transient tests. Additionally, for each area candidate for a production system, an extended well test is performed, with on-line interference tests with neighboring appraisal wells, aiming to evaluate the dynamic properties in terms of areal and vertical connectivity, as well as to anticipate potential problems regarding formation damage, fluid composition variation and flow assurance. Even with this comprehensive data acquisition, the complexity of reservoir rock sustains a large range of uncertainty in their properties, which will only be reduced throughout the productive life of the field. Therefore, the second pillar of the field development is built through a deep dive on the data by the geoscientists, in order to extract the geological attributes that impact the displacement and sweep efficiency of the oil. This goal is not always possible to obtain in a straight and deterministic way, but often through multiple possible scenarios. This is referred mainly to features as horizontal permeability distribution, presence of faults and barriers, vertical communication, fracture corridors, high permeability channels, among others. For the construction of the third pillar, a strong synergy between the disciplines of geoscience and reservoir engineering is necessary, so that the geological interpretation is incorporated and applied to the flow simulation model and, the most important, support the design of robust strategies to optimize oil recovery, under uncertainty conditions. When information is considered as perfect, it is immediately incorporated into the plan. Otherwise, multiple scenarios will persist for a longer period, making it necessary to apply strategies that can be effective in different conditions, and can be matched as soon as the real scenario is revealed. This paper describes the approach adopted for the development of the Pre-salt fields, supported by the aforementioned three pillars, and detail...

Introduction: geology of fractured reservoirs

“…The more recently discovered Cretaceous lacustrine reservoirs offshore Brazil (commonly termed "Pre-Salt) are also influenced by fractures (e.g. Salomão et al 2015) and have become a focus of exploration and production activity since 2006.…”

Relative permeability hysteresis analysis in a reservoir with characteristics of the Brazilian pre-salt

“…One of the great challenges of exploration in the Pre-salt involves the advanced recovery methods to be applied to improve the effective oil recovery from the reservoirs. The heterogeneity of carbonatic reservoirs, combined with high pressure and lithological complexity result in a low sweep efficiency, which decreases the productive efficiency of the reservoirs, leaving an undesired residual oil saturation (Salomão et al, 2015). Such concern increases with the application of the Water Alternating Gas -WAG injection pilot and the plans to extend the application of the method in the Pre-salt, as methods based on gas injection are objects of the poor sweep efficiency (Lima, 2021).…”