QUANTITATIVE RISK ASSESSMENT (QRA) OF AN EXPLORATORY DRILLING OIL SPILL IN DEEPWATER GULF OF MEXICO

摘要

Major offshore accidents such as Macondo well incident highlight one of the possible failure modes and subsequent disasters when an offshore engineering project could go wrong. Such events can potentially happen during any phase of an offshore well's life - starting from the exploratory drilling phase to the final phase of plug and abandonment. Major factors that significantly contribute in defining such accident scenarios are the geological and operational complexities, equipment reliability, human factors, geographical/economy location, and environmental conditions. The path taken by the reservoir fluids to reach the sea floor is also an important factor in determining the worst case discharge rates. It is expected that the environmental risks from an oil/gas spill would also be function of the type of hydrocarbons released and duration of the spill. A representative Neogene well is studied for quantitative risk assessment (QRA) for spill in exploratory phase from the Mississippi Canyon in the Gulf of Mexico with a water depth of 3,000ft and total vertical depth of 16,726 ft and the representative reservoir properties for this area are selected from the literature. Due to the large variation of reservoir properties, lognormal distributions have been assumed for some of the reservoir properties and from the Monte Carlo simulations P10, P50 and P90 values are estimated. Based on P50 and P90 values, the worst case discharge rates are calculated using a commercially available multiphase flow simulator with black oil model. Based on historical trends, release of hydrocarbons during blowouts are simulated for the following circumstances: seabed and topside releases, restricted and unrestricted flow through BOP, flow with drill pipe inside the wellbore and open hole flow without drill pipe and flow from the reservoir when it is either fully or partially penetrated. To incorporate the technological improvements and study their effects on the reduction of the overall risk associated with deepwater drilling activity, two cases are considered and compared to each other. First case is based on the historical data and the second case is a modified version of the first case by incorporating some of the recent technological improvements and newly built oil spill response systems e.g. capping stacks. The historical kick statistics and the equipment reliability data available in the literature is used to analyze various scenarios and corresponding flow rates. Risk is analyzed using the failure probability and consequence analysis and is presented in the form of a risk matrix for the different case studied and for the overall drilling activity as well.