Semi-quantitative Hazop Methodology Applied to Upstream Oil & Gas Activities

Recent off-shore drilling accidents showed that the consequence magnitude can be really disastrous; this suggest that a greater effort should be exerted to reach an advanced control of risks. In this framework this paper will show the advantages of a semi-quantitative HAZOP analysis applied to Upstream Oil & Gas operations. The paper will: •• Introduce and describe the use of semi-quantitative HAZOP analysis o Definition of likelihood and magnitude of consequences classes o Structure and characteristics of risk matrix o Definition of tolerability criteria; common and most used tolerability criteria o Use of risk matrix during HAZOP sessions to assess the tolerability of risk •• Apply the methodology to some examples to show how it allows more objective and consistent assessment, better evaluation of risk, protective measures and barriers o Example #1: off-shore oil reservoir drilling activities o Example #2: natural gas reservoir storage plants. The classic HAZOP technique relies on the experience, knowledge and judgment of team members to asses if the barriers available to protect from a given scenario can be considered enough; likelihood and consequence modelling are developed only later, outside the team. The semi-quantitative HAZOP introduces in the standard methodology the use of a risk matrix and a tolerability criterion. Likelihood classes and consequences classes will be defined, and they will be the x and y axis of the matrix. The likelihood of events can be easily evaluated since in the Oil and Gas sector a large set of statistical, highly reliable, well organized data is available (OREDA, OGP, E&P forum, etc.). The magnitude of consequences can be estimated using shortcut methods, or complete, detailed, complex consequence modelling (CFD, computational fluid dynamics models ), considering damages to people, the environment, the plant, company reputation, and so on. The tolerability criterion will be represented in the risk matrix dividing it in different areas, i.e. low risk (low frequency, low magnitude), unacceptable risk (high frequency, high magnitude), ALARP area. For each deviation, after indentifying a scenario, the likelihood and the magnitude of consequences classes are evaluated. It’s then possible to enter the risk matrix, verify the tolerability of risk, and find out if more barriers are needed. This preliminary quantification of the risk will take place involving all the team members, hence leading to more consistent and shared technical choices. The methodology will be applied to offshore drilling activities.