Preparing for the Worst – Expounding on Worst-Case Discharge (WCD) Evaluations for Niger-Delta Reservoirs

Abstract Globally, hundreds of well blowouts have been reported since the inception of oil and gas drilling activities. In Nigeria's Niger Delta, there have been around three major well blow-outs since 2000 with varying accounts of hydrocarbons spilled into the environment. These blow out incidences could cost over US$10M in asset losses, clean-up, and remediation. While preventing loss of well control is a key safety consideration in any well entry, the management of blow out incidences when they occur is equally important to minimize the environmental and social impacts. A key factor in preparing for effective management of well blow-outs is the accurate estimation of expected fluid volumes to be released from a blow-out well. Worst Case Discharge (WCD) in the upstream oil industry refers to the daily rate of uncontrolled flow of natural gas and oil from all producible reservoirs into the open wellbore. The assessment of the worst-case discharge rate at which hydrocarbons are being expelled due to full blowout is now a mandatory process safety requirement following the Macondo incident in the Gulf of Mexico in 2010. One of the learnings from that incident is that operators must now demonstrate that they are prepared to deal with the potential for a blowout. Thus, it is necessary to demonstrate that the blowout well, in its worst-case discharge condition, can be dynamically killed. This paper introduces typical evaluations for WCD rates in Niger Delta reservoirs, using case studies from normal pressure and high-pressured reservoirs. It demonstrates the dynamic kill calculations which are factored into the relief well planning. Best-practices in worst case discharge evaluations are elucidated. The objective of this technical paper is to strengthen prevention and preparedness for blow-out incidences in Nigeria. While it is true that safety checks have been increasingly tightened up since the previous blow out incidences, it is important to be continuously equipped for the ‘worst case scenarios.’