How To Develop a Well-Specific Capping-Stack Blowout Contingency Plan

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 181393, “How To Develop a Well-Specific Blowout Contingency Plan That Covers Engineering Analysis of the Deployment, Installation, and Soft Shut-In of a Subsea Capping Operation,” by Ray T. Oskarsen, SPE, Morten H. Emilsen, SPE, and Amir S. Paknejad, Add Energy; Mike Cargol, Trendsetter Engineering; and Kwee Choong See, SPE, Shell International Exploration and Production, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed. The planning process for developing a well-specific subsea-capping contingency plan involves assessing the feasibility of deploying a capping stack from a floating vessel, determining the weight and stability of the capping stack to overcome the force of the blowout jet, and performing dynamic-flow simulations of closing the capping stack outlets without loss of well integrity. This process not only assesses the feasibility, complexity, and risk exposure of the capping operation but also may justify further planning, studies, or expenditure. Introduction Blowout-kill techniques can be classified as either surface-intervention or relief-well methods. Relief wells aim to kill a blowout from the bottom by injecting fluid into the wellbore until the influx of formation fluid is stopped and the well is static when pumping stops. In many cases, a relief well will be the safest intervention and have the highest likelihood of success, and often it is considered the last line of defense against a blowout. Surface interventions are kill attempts aimed at controlling the discharge at the wellhead or at the fluid-exit point. An example is to install a capping stack on top of the wellhead and close its openings, which can be gate valves, chokes, or rams. Blowout Contingency Planning. Blow-out contingency plans ensure that people understand and can manage risks, thus ensuring safe and sustainable operations at all times. All blowouts are inherently different; thus, it would be both impractical and impossible to attempt to cover every possible blowout scenario in a contingency plan. For source-control planning, an operator should, at a minimum, address a worst credible scenario to demonstrate how the well will be brought under control. This scenario may be different from the worst-case discharge, which is used to estimate spill potential and necessary resources for containment and cleanup. As an example, if there is uncertainty about the gas/oil ratio (GOR), a low-case GOR may cause more oil spill, while a high-case GOR may make source control more challenging.