An Innovative Approach for Stochastic Analysis of Blowout Inventories and Impacts

Abstract

The uncontrolled eruption of a well is one of the most critical accidents that could happen in the oil and gas industry. Thanks to challenging R&D activities and collaborations, eni Upstream and Technical Services has developed and implemented Rainbow, an integrated methodology for blow-out risk analyses. As the Methodology has been applied in a wide range of HSE studies, the database of the analyzed blowout scenarios has been increasing for about 15 years, including for example release rates, total oil spill volumes and impact parameters (e.g. beached volumes for offshore scenarios and rainout area extension for onshore blowouts).Considering, for example, oil rates (BOPD), they could extend in a range as wide as 5 orders of magnitude, therefore a probabilistic analysis has been performed in order to evaluate the stochastic distribution of the above mentioned impact parameters.Applying short-cut models included in the Rainbow Methodology, the database of the analyzed blowout events has been integrated in order to include all potential scenarios. Moreover, in order to take into account both the local parameters affecting the well blowout frequency and the different flow paths (i.e. in-well geometry) distribution, a complete frequency assessment has been carried out.The stochastic distributions of the following parameters have been obtained as results:• total spill volume (all the scenarios).• extension of impacted areas involved in the oil fallout (for onshore wells).• length of impacted shoreline, oil volumes beached and open sea impacted area extension (for offshore wells, considering both underwater and atmospheric releases).The distribution curves have been clustered distinguishing among:• HPHT and normal wells.• Subsea and atmospheric.• Crude oil and gas condensate wells.The above information can be useful for several purposes, e.g.:• To categorize wells and potential blowouts in a rational risk ranking.• To support the Company clustering procedure focused on the cost evaluation of the blowout events. • To compare the blowout impact distribution with other accidents associated to hydrocarbon releases in the environment (e.g. tanker/ship, pipeline, storage, etc.)The comparison between the stochastic distribution curves and some real accidents (including Macondo blowout) occurred in the oil and gas industry is also presented in the Paper.