Decision analysis applied to petroleum field development is always strongly related to risk due to uncertainties present in the process. The appraisal phase of a petroleum field is characterized by several uncertainties, high investment and critical decisions. The use of numerical simulation allows a detailed study of the reservoir performance by several possible models obtained through a probabilistic approach. Methodologies to quantify the impact of uncertainties are still not well established due to the amount of variables that have to be considered and due to the computational effort that may be required. To make this process possible, some methodologies were developed to simplify a risk analysis. In this paper shows several details of a methodology that can be applied to complex and simple reservoirs in a reasonable amount of time to quantify the impact of the necessary simplifications, mainly by the selection of the ideal number attributes, discussing especially the influence:
gradual combination the less critical attributes in sensitivity study,
influence of the number of critical attributes.
The concept of representative models is selected to integrate the analysis with economic uncertainties. The simulations results in this process are combined to calculate the NPV (Net Present Value). After the statistical treatment of the results, it is possible to define the risk curve. This paper shows the importance of the simplifications and the number of simulation run besting the accuracy of the risk curve.
In petroleum exploration and production, a decision to be taken has to consider the risk involved in the process, which can be obtained by quantifying the impact of uncertainties on the performance of petroleum fields. The process is even more critical because most of the investments are realized during the phase in which the uncertainties are greater. The most important uncertainties are due to the geological model, economic conditions and technological developments. An applied risk analysis to a field on the appraisal phase should focus on quantifying the impact of geological uncertainties. Uncertainties on the economic conditions are always present in the petroleum industry. The methodology for risk analysis here is based on the work proposed by Loschiavo et al(1) and implemented by Steagall and Schiozer (2) that apply numerical simulation of several possible scenarios of the reservoir, combining the uncertain attributes. Other papers as Ligero et al (3), Santos and Schiozer (4), perform risk analysis using numerical reservoir simulation. Depending on the complexity of the problem, size of the reservoir and importance of the project, it's not possible include all uncertain parameters and, therefore, simplifications are necessary to yield viability of the process. The main objective of this work is to quantify the impact of some aspects of these simplifications, mainly by selection of the ideal number attributes. Other simplifications are: automation of the process, Ligero and Schiozer (5), and treatment of production strategy, Santos and Schiozer (4). All these authors have performed risk analysis with a fixed economic model in order to quantify the impact of geological model.