Abstract

Site-specific challenges related to water depth, geological and environmental conditions, rapid technological development and increased demands with respect to cost effectiveness and environmental consciousness are all factors that impact the uncertainty picture related to drilling and well operations. Thus risks related to undesirable outcomes such as kick and blowout are also influenced. It is however questionable whether the ruling practices for use of quantitative risk analyses in planning of the operations keep up with this development. As the nature of the operations change drastically, use of overall statistics from earlier incidents hardly provides a satisfactory basis for decision making. Such statistics does not reflect the exposure of the specific well to the various kick and blowout mechanisms or the effect of measures introduced to reduce the probability of these mechanisms to occur. KickRisk, a new risk analysis tool with focus on kick and blowout is developed in order to improve the basis for risk-based well control planning. The idea behind this tool is a more detailed system modeling, which enables the planning to include more well- and operation-specific information in the analyses and to obtain a more differentiated risk description. Uncertainty is expressed through probabilities related to factors at a detailed system level and is propagated in kick and blowout probabilities through the logic of the model structure. The intention of this paper is to discuss the requirements for risk analysis methods with respect to kick and blowout in well planning and how these can be met in practice. The principles of the new tool KickRisk are described and the experiences from case studies on real wells are presented.

Introduction

Having the potential to result in catastrophic consequences with respect to the lives and health of personnel, the environment, assets and economic values, blowouts represent the most feared and unwanted phenomena that might result from drilling and well operations. In operations not involving production, taking a kick represent the first barrier lost in the development of a blowout. Even if well control is retained, kick incidents in themselves often imply considerable costs in terms of:

  • increased rig costs and lost production due to several days delay

  • additional operation costs related to the well control activities

  • reduced production or recovery actions as consequence of well or formation damage inflicted by the kill operation

  • loss of credibility in the marked.

Avoiding kicks and blowouts are basic objectives in well design and operation planning. Characteristic for probabilistic planning against these events is dealing with uncertainty associated with a great number of factors related to local geology, the performance of equipment and human actions. This uncertainty implies that some probability of taking a kick, which again might develop into a blowout scenario, follows any well operation. In planning of traditional operations in areas with normal pressure regimes the uncertainty has to a large extent been handled by good industry practices involving application of rules of thumb and safety factors developed through experience and standard engineering methods. Even for more complex wells the industry has so far mainly used deterministic approach, applying physical models for kick and blowout development. For example, advanced deterministic kick simulators1,2 are used to plan casing setting depths and for kick tolerance evaluations in the design phase as well as during operations. Some evaluate possible scenarios by playing "what-if" games with realistic simulators.

Probabilistic methods taking uncertainty into account more explicitly are also applied in various parts of the planning process. Examples are use of standard reliability analysis in design of critical well control equipment and methods of structural reliability in casing design.

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