BlowFlow - Next Generation Software for Calculating Blowout Rates
Authors: Karlsen Hans Christian , Ford Eric P. 
Published: March 2015

A blowout is known to be the most severe event that can happen during explortation of petroleum resources. Oil-spill preparedness is important in general, particularly in the arctic region where uncertainties about consequences are high and contingency planning for major accidents requires extra attention. Calculation of blowout rates and durations from potential blowouts is an important part of environmental risk management, both in the planning phase of a well and during other well activities.

BlowFlow is a software tool that has been developed for risk based evaluation of blowout scenarios in order to quantify blowout flow rates, volumes and durations. The results can be used as input to Environmental Risk Analysis, to dimension the emergency preparedness organization and identify both probability and consequence measures in the oil-spill preparedness planning. BlowFlow is meant as a cross-disciplinary tool for communication between petroleum, reservoir, drilling and HSE engineers. The basic design has been inspired by the guidelines given in [1]. Based on a fixed definition of potential blowout scenarios, BlowFlow provides probability distributions of potential blowout rates, durations and volumes for that can be used as input for the Environmental Risk Analysis. Since there are large uncertainties involved at the stage when such an analysis is performed, a stochastic modeling approach is used, i.e. Monte Carlo simulations and spline interpolations, based on multi-discipline expert input.

Introduction

Operators on the Norwegian Continental Shelf (NCS) are required by law to document the risk of petroleum activities as well as using this information for managing and reducing risk where applicable. Examples of risk analyses performed are Environmental Risk Analysis (ERA), Oil Spill Response Analysis (OSRA) and Total Risk Analysis (TRA), the latter for fields only. Today's practice in oil companies varies with respect to level of detail, assessment of uncertainty, nomenclature, documentation and traceability of the analysis. Due to the lack of relevant international and national standards, the Norwegian Oil and Gas Association has developed guidelines, c.f. for example [1], [2] or [3], based on a reference methodology in order to standardize nomenclature, procedure and documentation of blowout calculations.

An ERA consists of a combination of probabilities for oil spill scenarios and corresponding blowout rates and durations, inducing a potential environmental damage. Oil drift models contribute to calculate damages of Valuable Ecological Components (VEC; for example fish and fish habitats) in the area of influence, and the time of restitution for the most vulnerable stock in the influence area is used to define the acceptance criteria for an activity. OSRA includes plans for consequence reducing measures and type and quantity of response resources needed. Efficient oil pollution response capability will reduce free oil on the surface, thereby reducing the total area of influence. Important inputs include geographical location, scenarios for oil spill and corresponding probabilities, type of operation, blowout rates and durations, oil type, wind and currents, time of year and VEC. In a Total Risk Analysis (TRA) and well killing context, potential gas release/blowout followed by loss of lives and structures are of interest. In the risk analyses previous mentioned, calculating realistic blowout rates and the duration of a blowout are important for the following analysis.