Well-specific Blowout Risk Assessment

Abstract

As oil and gas projects explore more and more challenging territories, and as public opinion is increasingly aware of risks from drilling operations, it is of furthermost importance to better understand and systematically manage these risks.For every well project on the Norwegian sector, the risks from a blowout are studied from the safety and the environmental perspective, through Quantitative Risk Assessments and Environmental Risk Analyses, respectively. The blowout characteristics (probability, flow rates, durations) are among the most influent input parameters for these analyses. Traditionally these parameters have been extracted from available historical statistics from blowout databases. These databases provide generic data with very limited consideration for the well and operation specific characteristics (e.g. exploration, development, HPHT).DNV has developed a methodology for the assessment of blowout risks in order to better understand them and to be able to provide a more realistic risk picture. A multidisciplinary approach is applied during the risk assessment process, assessing the drilling or well operations according to a set of predefined criteria or risk factors. This benchmarking analysis is used as a basis for assessing the probability of a leak or a blowout. Well flow simulations are used and adjusted in order to assess the well specific leak and blowout rates for the different operations. The potential leak and blowout durations are calculated using statistical models and taking into account the context of the drilling and well operations.This new method considers the field specific reservoir challenges, best available technology and best operational practices in order to generate a more field and operation specific risk exposure. The results are more accurate risk predictions. Traditional analysis may be too conservative and would typically not reflect the actual well conditions, barriers and operational steps. Relevant examples from the Norwegian sector are presented.

Probabilistic analysis of risk and mitigation of deepwater well blowouts and oil spills

“…We list these in the following by considering the floating rig and year of occurrence as identifiers : Sedco 135G 1969;Sedco 135F 1979;Sea Quest 1980;Petromar V 1981;Vinland 1984;Treasure Seeker 1984;West Vanguaard 1985;Ocean Odissey 1988;Treasure Saga 1989;Actinia 1993;Jim Cunningham 2004;Sedco 700 2009; Deepwater Horizon 2010. The method we employ to assess time and probability of occurrence of subsequent events is equivalent to the so-called well-specific risk assessment used to assign a risk level to each well type considered in the study of Vandenbussche et al (2012).…”

“…To project historical documented data into a future setting, we introduce risk factors f (Vandenbussche et al 2012) A score Sb, f is then assigned to each risk factor f of blowout b. Table 2 lists the criteria of scoring risk factors f. We subdivide these into three classes (1-3) according to an increasing risk level.…”

“…An approach is grounded on SINTEF and/or Scandpower historical statistics, that include the extinction of the release by external causes (i.e., well bridging, coning, natural depletion). Most of the recent works published after the Macondo accident (Rasmussen 2011;Dyb et al 2012;Johnsen 2012;Vandenbussche et al 2012Vandenbussche et al , 2014Jouravel 2013) follow a different approach, i.e., the complete blowout extinction (with no possibility of partial flow reduction) is related to: (a) the bridging of the well (with probability and occurrence time estimated from historical data) and/or (b) the application of blowout stopping techniques available at the time of the accident (surface killing methods, subsea capping stack, killing by relief well), each with its probability of success and intervention time calculated according to a series of assumptions. Neglecting the possibility to consider partial reductions of blowout flow rate is a notable limitation.…”

“…Among the most recent works on the subject, we refer here to Brude (2007), Brandt et al (2010), Kruuse-Meyer et al (2011), Rasmussen (2011), Ji et al (2012, Dyb et al (2012), Johnsen (2012), Jouravel (2013), Vandenbussche et al (2012Vandenbussche et al ( , 2014, Ahluwalia and Ruochen (2016), and Ruochen et al (2016) and references therein.…”

Dynamic Blowout Risk Analysis Using Loss Functions

“…Case‐specific data are used to update the generic data used in risk assessment during the design phase of the system . Vandenbussche et al . developed a well‐specific blowout risk assessment methodology for determining the blowout probability by considering the flow rates and duration of the blowout as well as risk factors such as pressure margins, permeability, pore pressure, drilling crew experience, cement performance, and logging runs in adjusting the blowout probability to reflect the existing well condition.…”