Comprehensive Methodology to Evaluate Blowout Probability Through the Combination of Geological Uncertainties, Human Errors and Equipment Reliability

Abstract

Abstract The most significant threat to oil exploration and development is an uncontrolled release of reservoir fluids during drilling operations, commonly called a blowout. Besides its tragic environmental and human impacts, Macondo accident fostered the awareness in the industry that blowout risk goes further the idea of an implicit risk of drilling activities: blowout is an operative risk to be properly assessed, as reported in the European Directive 2013/30/EU on offshore operations. In order to tackle such request, Eni developed a standardized methodology called e-wise™ (eni Well Incident Systematic Evaluation) that provides an objective and reliable assessment of blowout risk. As a prelude, the common criteria based on statistical occurrence of blowout was considered neither exhaustive, nor accurate. Actually these statistics are suffering from many limitations: limited time span, outdated technologies, inconsistent environment (now deeper wells), variety of technical approaches, and no consideration of risk exposure duration. ENI decided to measure blowout probability with a comprehensive methodology accounting for the three key elements affecting blowout occurrence: geological uncertainties, equipment reliability and human errors. The methodology put together automatically in properly designed fault tree, the three root causes and it applies them on specific well designs. The result of this approach is a standard way to calculate blowout risk that can be applied on rig/rigless operations, supporting well engineering and permitting process. This solution, named e-wise™ is able to generate two types of standard outputs: full breakdown of blowout frequency by section/flowpath and extensive bow-tie for communication and certification purposes. The full breakdown of blowout frequency allows the engineering and the operations to focus their attention on the most critical phases of the well. The model can be used for further sensitivity analyses foreseeing alternative operating procedures or additional safety technologies in order to have an univocal assessment of their benefits in term of blowout probability reduction. As a matter of fact, specific R&D programs are assessed through e-wise™ to address their potential value in terms of safety improvement. The bow-tie depiction of the results provides a synthetical representation of all detailed calculations, where some models encompass more than 20 scenarios, each one having dozens of sub components. A bow-tie supports the communication of the results toward management and authorities by giving a complete vision of the blowout with the relative reliability of safety barriers and the different impact scenarios including containment and relief strategies.