At the time of selecting the development plan of a petroleum field, little information is available and the range of uncertainty is large. Once the main variables that most strongly affect the production behavior have been identified, the next step consists in generating the set of possible results for production forecast, and obtaining the probability distribution of the economical parameters, as the net present value (NPV). Depending on the range and nature of the uncertainty variables, the best way to protect the project, instead of collecting information, may consist in changing the exploitations strategy, in order to reduce reservoir risks. In next phase of exploitation of Marlim Sul field, Campos Basin, Brazil, the main source of uncertainty is an extensive fault, located in the middle of the reservoir, which breaks the oil zone into two blocks. According to the strategy of the original plan, the injection wells are located on one side of the fault, while the production wells on the other side. The sealing capability of this fault is a critical issue, since it could be an obstacle to oil sweeping by the water injection. To face this issue, we have two alternatives: either collect more information in order to reduce the level of uncertainty, or select an alternate plan, less sensible to transmissibility of that fault, and more adequate to the various scenarios. To compare these alternatives, we utilize uncertainty analyses, enriched with risk aversion considerations. The use of the expected monetary value (EMV) as parameter of comparison proved to be a good way to meet better all the scenarios, but not sufficient to traduce the economic risk of the project. The use of concepts of the utility theory indicated that the alternate plan has lower sensibility to critical uncertainty, is more protected against reservoir risks, and is the best development strategy to be implemented. Introduction The selection of the best development project of an oil field is mostly accomplished with base on limited data available, in a scenario of large uncertainty about reservoir properties, mainly those related to fluids volume and flow capacity. This is an intrinsic feature of the petroleum industry, where data collection, such as well drilling, formation tests or seismic acquisitions, requires quite high cost investments. The adopted exploitation strategy is the one that reach the maximization of economical parameters, like the net present value (NPV), when applied to the most likely reservoir scenario, which show the expected values of the properties linked to geometry and fluid flow in porous medium. When the range of uncertainty is high, this strategy reveals not being efficient, since the adopted project is the best for the moderate scenario, but may be inadequate for other scenarios, such as, for example, the pessimistic one. In this case, protective and risk reducing action should be undertaken. The use of expected monetary value (EVM), which represents the values of NPV of each scenario, weighted by its probability, is a more consistent parameter to help the selection. An alternate strategy, less sensible to sources of uncertainty, apparently is more adequate, even having a lower NPV in the most likely scenario. Nevertheless, even the utilization of the EMV parameter may not be sufficiently robust to indicate the best option to be pursued. While analyzing aspects of risk aversion, it can be noticed that, in a general sense, deficits resulting from a pessimistic scenario are fare more serious than simple economical losses. Further questions may be involved, such as company image, team motivation, and even company survival. To represent issues of this nature, the preference or utility theory and the concept of utility function are tools of great value and are applied here for the decision making process. The objective of this paper is to present a comparison between oil field development strategies, under conditions of high reservoir uncertainty, utilizing, as base the EMV, conjugated to concepts of utility function. The target field is Marlim Sul, located in the Campos Basin, Brazil. In the following sections, we describe the reservoir aspects, its critical sources of uncertainty and the strategies for oil recovery to be compared. Subsequently, the methodology for strategy comparison is presented and, lastly, the practical application and the results analysis.

In petroleum industry, scarce information is available at the time of adopt the exploitation strategy, and the expected production profiles comprise a high level of uncertainty. Depending on the range of the uncertainty variables, the best decision may be to collect more information by drilling more wells, performing a new seismic acquisition or making long term tests. But, sometimes, the best way to protect the project is to assume an uncertainty-proof development strategy. These ideas were applied to help decision in two real cases, in Marlim Sul field, Campos Basin, Brazil. In the first case, the main uncertainty source is the quality of the flow transmissibility between producers and injectors wells. If that communication is restricted, the production decline is more accentuated and the best strategy would be to place the injectors nearer the producers, although the displaced oil is reduced. In order to elect the best strategy, we have compared two different plans containing different positions of injector wells, applied to three different scenarios of flow transmissibility. In the second case, we have a channeled reservoir, with an extensive fault in the middle, the transmissibility along which is unknown. In a scenario of good communication, the best strategy is to position the injectors on one side and the producers on the other side of the fault. But in scenarios of restricted communication, the best scheme could be to place injectors and producers on both sides of the fault. To make the best decision, we have used different plans, applied to different scenarios. The results demonstrate that, in both cases, the alternate plan has not the higher net present value (NPV) in the moderate scenario, but presents the higher expected monetary value (EMV), having also a lesser sensitivity to the reservoir uncertainties, being more protected to the risk. In both cases the original plan has been abandoned and the alternative plan started being implemented. Introduction The definition of the development project of an oil field is generally made with basis on insufficient information and under conditions of a great uncertainty as to the geologic parameters that characterize the fluid volumes and the flow properties. The adopted strategy is generally the one that produces the maximization of the fluids recovery, or the maximization of the economic parameters, when applied under the conditions regarding the most likely scenario. This scenario comprises the most representative image of the reservoir, with the most expected values of the properties related to the geometry and the flow of fluids in porous medium. After that, the analyses for characterization of uncertainty in the production curve, and also in the economic parameters, are carried out, with basis on the previously fixed project. But this strategy may not be the most adequate, mainly if the uncertainties comprise a substantial range and if the application of the same strategy, under the conditions of the pessimistic scenario, reveals very serious consequences and very low economic results. An alternate strategy, less subject to these uncertainty sources, could be a more adequate option, even being economically less valuable and less appealing in the moderate scenario. The purpose hereof is to present the application of a methodology of comparison and decision upon the best strategy for the recovery of oil, in scenarios of great uncertainty in the reservoir properties. The target field is situated in Campos Basin, Brazil, and two of its main development projects have been analyzed. In the items hereafter some details on the field and its reservoirs, its main uncertainty sources and the strategies for the recovery or oil are presented. Following is it described the methodology of comparison of the strategies and, at last, the results of their application in two projects of the field. Proposal of the problem: the field and its projects Marlim Sul field is a turbiditic complex formed by channels, lobes, crevasse and spill deposits 1. It is composed of fifteen reservoirs blocks of eocenic, oligocenic and miocenic ages, with excellent characteristics of porosity and permeability, and oil ranging from 15 to 25 API.

This paper addresses the innovative appraisal strategy applied to the Libra project; located in ultra-deep waters offshore Brazil. It details the key role of the Extended Well Test (EWT) Program, within the field overall Risk Mitigation Plan, as well as its interfaces with additional appraisal activities. The Value of Information (VoI) for the main acquired data is described, highlighting the associated impacts for the full field development and validation of the enhanced recovery strategy. A case study approach details how the whole EWT project maximized the acquired information, mainly from a reservoir point of view. Although the EWT approach is not new to Petrobras in the offshore environment, this is the first one with simultaneous oil production and gas reinjection. Several reasons justify the use of the industry’s first dedicated offshore EWT system with this capability. Gathering data on the main dynamic parameters of the field was critical to speed-up the development, with an acceptable risk level. The incorporation of these data in the reservoir models and the impacts in the most relevant development decisions are also described. The chosen methodology brought many opportunities, as well as challenges to interpret the data and to incorporate them in the reservoir models. Furthermore, the capability to produce without continuous gas flaring makes it possible to apply such approach anywhere else in the world.

fax 01-972-952-9435. AbstractDeep offshore oil production demands very high investments (CAPEX) so its development must rely on a careful planning. This frequently takes place in a setting with very limited amount of information due to high costs of appraisal operations. The figure becomes even more complicated when heavy oils are the target: low energy reservoirs require water flooding which, in turn, reflects in low recoveries and excessive water handling, not to mention other production problems.This paper highlights different simulation studies that have been performed in order to set up an economical development plan for a 16 API 1700m water depth oil reservoir offshore Campos Basin. The main reservoir consists of a high thickness turbidite channel crossed by a N-S fault whose hydraulic conductivity is the main uncertainty. Vertically the reservoir is composed of three zones, where the upper one has a gas cap partially in contact with the two bottom ones. These structural complexities required a detailed study for positioning injectors and horizontal producers based on a decision tree analysis.