Hydraulic Blowout-Control Requirements

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 105612, "Hydraulic Blowout- Control Requirements for Big-Bore and HP/HT Developments: Validation With Field Experience," by P. Oudeman, SPE, Shell Intl. E&P, prepared for the 2007 SPE/IADC Drilling Conference, Amsterdam, 20–22 February. The full-length paper presents equations and guidelines for determining requirements for pump rates, number of wells, and kill fluids required to kill a blowout. A comparison with selected field cases demonstrates that the formulated guidelines match the requirements to actually kill these blowouts. This comparison gives confidence that the guidelines presented are a good starting point for contingency planning. Several blowout scenarios for a giant North Sea gas field are examined to demonstrate application of the guidelines. Introduction Because of advances in drilling and production technology, blowouts have become an increasingly rare phenomenon. A report published by the United Nations Environment Program that cites statistics from the US Gulf of Mexico (GOM) and the North Sea shows the probability of shallow-gas blowouts in exploration wells to be approximately one in every 200 wells; for workover operations, one in every 2,500 wells for oil wells and one in every 1,000 wells for gas wells; and for infill wells, less than one in every 10,000 wells drilled. Because of this, blowout prevention is a top priority in drilling and well intervention. A contingency plan must be formulated before spudding development wells to limit the consequences of a blowout by prescribing an adequate emergency response to a possible well-control incident. On the basis of the emergency-response plan, preparations can be made to take action rapidly after an incident is reported. Such preparations would include ensuring the availability of a nearby rig for drilling a relief well, sufficient tubular-goods stock to complete a relief well, and pump capacity to kill the blowing well. With these elements in place, relief efforts can be started quickly, thus reducing the time to regain control of the well. The plan should consider the possible modes of failure and the response to these failures to restore well integrity. In the majority of cases, "capping" of the well (i.e., replacing the damaged wellhead) is the most efficient method to stop flow from the well. To illustrate, most of the more than 780 wells that were sabotaged and set on fire during the 1991 Gulf War in Kuwait were brought under control within 8 months by capping. With this success, well-control companies demonstrated that even under harsh post-war conditions, capping technology could deal with almost any form of wellhead damage.