Oil drilling projects are planned assuming that the duration and cost of activities can be accurately estimated once methods, technologies, resources and expected targets are clearly defined. In reality, the success of drilling can be affected by many factors and events, most of which can not be exactly predicted; therefore a proper estimate of expected revenues and possible losses is important in order to evaluate the economic feasibility of a drilling project and to achieve better performances. This paper focuses on the development of a simulation model of drilling activities using a technique alternative to the Monte Carlo method, the standard simulation method currently used for quantitative risk analysis. Discrete Event Simulation (DES), performed with Arena Rockwell Software, starts from offset wells' historical data to derive probabilistic distributions of key variables of the drilling process, such as rate of penetration, drilled meters per run, generic activities duration, likelihood of drilling problems. It allows the project planners to consider both the sequence of operations and cause-effect links between events: in this way deviations from the planned duration and cost due to combinatory effect of general uncertainties and specific risks associated to the project can be assess and mitigated. In this paper, both methods of analysis have been used to evaluate a challenging drilling project which represents the first application to a highly deviated well of the Extreme Lean Profile technique, an innovative drilling technology developed by Eni. The lack of historical information for this experimental technique along with the complex geological features of the region, highlight the need for performing a thorough risk analysis on both the usefulness of the new drilling technique and the potential exposure to relevant risks

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