Modelling and Management of Annular Surface Blowouts - An SPDC Case Study

Abstract

This case study describes the planning and execution of a surface gas fire blowout control operation that resulted in re-entering, killing and abandoning a wellbore that was blowing out at the surface via the annuli "A and B" at an SPDC well blowout. As part of the kill plan, simulations by use of the dynamic two-phase pipe flow simulator OLGA were performed. This paper presents the principles of the kill simulator and how the results were used in the design of the kill operation. A comparison with observed data and actual result are presented. The challenges faced include, accessing the wellhead due to the raging gas fire, obsolete wellhead, vandalised wellhead entry points, and absence of top packer in the original completion are highlighted in this paper. The techniques and equipment employed, plus good teamwork, provided the necessary ingredients to divert the gas fire and gain access to the wellhead thus enabling killing, securing and partial abandonment of the well. Introduction After a blowout, everyone wants to find the cause, prevent recurrence and understand how it was controlled. In-house papers/documentations may be written, measures are introduced to prevent another occurrence and be better prepared next time. In time, experience is lost as individuals leave and conditions become ripe for another blowout. Therefore, it is important to record, publicize, discuss and review case histories and past actions to learn about and prevent future disasters. Failure to use available information, not a lack of knowledge, usually causes and can certainly worsen disasters. This article is meant to disseminate information on an SPDC well blowout, analysis of causes, control methodology, etc., which will prove useful in educating and helping to avoid the disasters of blowout control in another well or region. Surface control operations are normally more difficult to develop due to the many possible blowout scenarios; potential escalation and unknown well response associated with intermediate control steps. For example:removing debris from Wellhead area;extinguishing fire;capping and diverting wellhead;shut-in and bullhead well dead ordynamically kill well. At these points additional information is gained that guides the team to the course of action required to meet the next milestone (1).