Ultra-deepwater blowout well control analysis under worst case blowout scenario * Zhaoguang Yuan * , Yahya Hashemian, Daniel Morrell Schlumberger, 5599 San Felipe Street, Suite 100, Houston, TX, USA article info Article history: Received 9 June 2015 Received in revised form 22 August 2015 Accepted 22 August 2015 Available online xxx Keywords: Blowout well control Dynamic kill simulation Relief well Worst case blowout Worst case discharge abstract Because of the high frictional pressure losses in kill lines in ultra-deep water wells, it is challenging to control the blowout under worst case blowout scenarios. The operational parameters need to be carefully controlled to avoid exceeding the operational limitations such as breaking the formation or exceeding available pump pressure limit. In this study, dynamic kill simulations of multiphase flow are carried out to evaluate the operational parameters during the kill process. The simulations account for transient changes including frictional pressure losses, u-tube effect and fluid density variations. By optimizing the operational sequence with regards to, kill mud density, pump flow rate, pump down staging, relief well drillstring and trajectory, blowout can be controlled without exceeding the operational window. This paper shows that 10,390 bbls of the kill mud, 8000 psi pump pressure limit, optimum flow rate arrangement, and minimum 270 min required to get full kill mud return to the sea floor during the well kill operation. Through the aid of advanced transient software models, assessment of the required ca- pacity to kill a blowout enables development of realistic contingency plans to ensure that well control can be re-established in case of an ultra-deep water worst blowout scenario. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The Bureau of Safety and Environmental Enforcement (BSEE) defines deepwater as water depths of at least 500 feet, and ultra- deepwater as water depths of 5000 feet and deeper. Gulf of Mexico (GOM) ultra-deep water oil production has risen signifi- cantly since 2004 and more than tripled since 2005 (U.S EIA annual report, 2009). For ultra-deep water operations, the challenges involved with every step, from casing design, drilling (Rohleder et al., 2003), cementing (Mishra, 2006), completion, and perfo- rating (Wendler and Scott, 2012), to production. Since June 2010, Bureau of Ocean Energy Management (BOEM) required operators to calculate a worst case discharge scenario to apply for a drilling permit. The worst case discharge is defined in NTL No. 2010-N06 as “The daily rate of an uncontrolled flow from all producible reservoirs into the open wellbore”. The NTL No. 2010- N06 indicates that the worst case discharge scenario should include all hydrocarbon-bearing zones in each open-hole section as it is planned to be drilled. The uncontrolled flow is up unobstructed casing and liner, no drill pipe in the hole. Worst Case Discharge Scenario (WCD) rates for deepwater wells should be based on un- controlled flow at the sea floor with a hydrostatic water column or atmospheric pressure at sea level if well work is on an existing platform. Even there are wellbore stability issues (Willson, 2012; Willson and Sharma, 2013) during blowout, bridging is not considered by Bureau of Ocean Energy Management (BOEM). For ultra-deep water wells, the well control contingency planning and casing design needs to be carefully reviewed to meet the worst case discharge criteria. Located at GOM Keathley Canyon block 919 and 736, water depth around 7000 ft, at least two wells were reported by Bowman (2012) and Moyer et al. (2012) that an existing well design had to be significantly altered to meet the new worst case discharge criteria. Many blowout simulators have been developed to estimate the blowout rate and calculate blowout control hydraulic parameters. A blowout simulator (Santos, 2001) developed in FORTRAN to model blowout rate and dynamic kill technique using a relief well. During the blowout, the water buoyancy can be affected by the oil and gas plume (Adams and Economides, 2003). A comprehensive hazard and operability analysis, including risk assessment, is reported by Lage et al. (2006) to perform blowout rate calculations and relief * This paper (SPE 170256) was accepted for presentation at the SPE Deepwater Drilling and Completions Conference, Galveston, Texas, USA, 10e11 September 2014, and revised to publication. * Corresponding author. E-mail address: zyuan1@slb.com (Z. Yuan). Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse http://dx.doi.org/10.1016/j.jngse.2015.08.047 1875-5100/© 2015 Elsevier B.V. All rights reserved. Journal of Natural Gas Science and Engineering xxx (2015) 1e8 Please cite this article inpress as: Yuan, Z., et al., Ultra-deepwater blowout well control analysis under worst case blowout scenario, Journal of Natural Gas Science and Engineering (2015), http://dx.doi.org/10.1016/j.jngse.2015.08.047