Deepwater Horizon Explosion

Note: This post summarizes the incident occurred one month ago. The context is partially modified from Deepwater Horizon and some other relative terms on wikipedia.org.

On April 20, 2010, an explosion occurred on Deepwater Horizon, an offshore rig owned by Transocean and leased by BP, and it caught fire.[1] Two days later, it sank in water approximately 5,000 feet (1,500 m) deep, and has been located resting on the seafloor approximately 1,300 feet (400 m) northwest of the well .[2]

INTRODUCTION

Deepwater Horizon is a Reading & Bates Falcon RBS8D design, Hyundai Heavy Industries build, 5th generation deepwater semi-submersible drilling unit capable of operating in harsh environments and water depths up to 8,000 ft (upgradeable to 10,000 ft) using 18¾in 15,000 psi BOP and 21in OD marine riser.[3] Construction started in December 1998 and it was delivered in February 2001 after the acquisition of R&B Falcon by Transocean. Since arriving in the Gulf of Mexico, Deepwater Horizon was under contract to BP Exploration. Its work included wells in the Atlantis and Thunder Horse fields, a 2006 discovery in the Kaskida field [4] and the 2009 Tiber oilfield.[5] In 2002, the rig was upgraded with “e-drill”, a drill monitoring system where technicians based in Houston, Texas receive real-time drilling data from the rig and transmit maintenance and troubleshooting information.[6] On September 2, 2009, the giant offshore rig drilled on the Tiber oilfield the deepest oil and gas well ever drilled with a true vertical depth (TVD) of 35,050 feet (10,680 m) and measured depth (MD) of 35,055 feet (10,685 m), of which 4,132 feet (1,259 m) was water.[7] In October 2009 BP extended the contract for Deepwater Horizon by three years, to begin in September 2010.[8] The lease contract was worth $544 million, a rate of $496,800 per day.[9]

Fig. 1 Deepwater Horizon Offshore Rig

BACKGROUND

Before the accident, it worked on BP’s Mississippi Canyon Block 252, referred to as the Macondo prospect.[10] The rig caught an explosion when it was last located approximately 41 miles offshore Louisiana on Mississippi Canyon block 252. [11]

Fig. 2 Location of Deepwater Horizon [12]

EXPLOSION

Though the cause of the explosion on the Deepwater Horizon remains under investigation, officials with Transocean have said a blowout within the deep oil well was likely to blame for the deadly blast. At the time of the accident, half of the crews were cementing, and the other half were installing casing to secure the walls of the well. [13] It was the rig in the final phases of drilling a well in which casing is cemented in place, reinforcing the well. This is a delicate process as there is the possibility of a blowout, the uncontrolled release of formation fluids from the well. [14]

The fire reportedly started at approximately 10 PM CST on Apr. 21, 2010. [11] Adrian Rose, a vice president for Transocean Ltd., said that there was “no indication of any problems” as crew members carried out routine work around the drill site before the blast. Officials said 126 people were on board at the time of the explosion. Of the 115 accounted-for workers, 17 injured were evacuated by helicopter from the rig, and another 94 people were taken to shore with no major injuries, and four more were transferred to another vessel, according to the Coast Guard. The rest of 11 were missing. [15]

Fig. 3 Deepwater Horizon was on fire[16]

Fig. 4 Deepwater Horizon was on fire[16]

According to survivors words, the sudden explosion gave them less than five minutes to escape as the alarm went off, and Chad Murray, 34, the rig’s chief electrician said he didn’t think any of the missing could have survived. [17]

The United States Coast Guard (USCG) launched a massive rescue operation.[11] One day after the explosion USCG spokesman Mike O’Berry said four helicopters, four Coast Guard boats and a plane were helping search for the missing workers. [18] Two USCG cutters continued the search overnight. By 6 AM of Apr 22, USCG has surveyed 1,940 square miles in a series of 17 separate air and sea search missions since the Tuesday explosion. [19] Official confirmed Murray’s word on Thursday and USCG stopped the search for the 11 missing persons. [20]

Fig. 5 United States Coast Guard Rescued the Wounded[19]

After the blast, the rig was tilting as much as 10 degrees. [21] Fire boats sprayed the rig with water in an unsuccessful bid to douse the flames. After burning for more than a day, Deepwater Horizon sank in water approximately 5,000 feet (1,500 m) deep, and has been located resting on the seafloor approximately 1,300 feet (400 m) northwest of the well on April 22, 2010. [2]

Fig. 6 Anchor Handling Tugs try to extinguish the oil rig explosion blaze on the Deepwater Horizon[16]

Fig. 7 Anchor Handling Tugs try to extinguish the oil rig explosion blaze on the Deepwater Horizon [19]

INVESTIGATION

On the day Deepwater Horizon sank on the bottom of Gulf of Mexico, the USCG and the Minerals Management Service launched an investigation on possible causes of the explosion. [22] According to interviews with rig workers conducted during BP’s internal investigation, a bubble of methane gas escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before exploding.[23] The blowout preventer (BOP, a huge and complex tower of valves and pipe crimpers on the ocean floor designed to shut down a well in an emergency) was supposed to activate once the escaping gas was detected and the alarm went off, but unfortunately it didn’t work. Bob Fryar, senior vice president of BP’s exploration and production operations in Angola, in southwestern Africa said BP had found there were some leaks on the hydraulic controls on the BOP, though it is unclear whether it caused the malfunction. [24]

AFTERMATH

Shortly after the explosion, the concern about the crude oil spill from the incident on the environment became more and more serious because the failure of BOP caused the oil leakage from the borehole.[25] Since BP has taken several measures (1. A remotely operated underwater vehicle attempting to turn on the Deepwater Horizon blowout preventer;[26] 2. BP now aims to deploy a small “top hat” dome over the leak after its effort over the weekend to cover it with a huge metal box was stymied by a buildup of crystallized gas hydrates;[27] 3. After several attempts, BP successfully inserted a 6 inches wide tube into a jagged 21 inches pipe that is leaking oil onto the Gulf seabed, which is surrounded by a rubber seal and attached to a tanker at the surface.[28]) to stop the oil leakage from the borehole, the spill is expected to eclipse the 1989 Exxon Valdez oil spill as the worst US oil disaster in history.[29] BP is leading the clean-up work of oil spill, and working with US government, communities, and organizations. [30]

Fig. 8 A remotely operated underwater vehicle (ROV) attempting to turn on the Deepwater Horizon blowout preventer[26]

Fig. 9 The oil slick as seen from space by NASA’s Aqua satellite on April 25, 2010 using its Moderate Resolution Imaging Spectroradiometer (MODIS) instrument[31]

Reference:
1. Oil rig explodes off La.; 11 missing, 17 hurt
2. Transocean Oil-Drilling Rig Sinks in Gulf of Mexico (Update3)
3. Fleet Specifications: Deepwater Horizon
4. BP & Partners Make Discovery at Kaskida Prospect in the Gulf of Mexico
5. Deepwater Horizon Drills World’s Deepest Oil & Gas Well Deepwater Horizon
6. Monitoring system reduces rig downtime
7. Transocean says well at BP discovery deepest ever
8. Deepwater Horizon contract extended
9. THE WELL
10. Offshore Field Development Projects: Macondo
11. Transocean Ltd. Reports Fire on Semisubmersible Drilling Rig Deepwater Horizon
12. Eleven workers missing after La. oil rig explosion
13. ‘Cementing’ of rig’s well eyed as possible culprit in blowout
14. Deepwater Horizon – A Failure of Well Control
15. At least 11 missing after blast on oil rig in Gulf
16. Deepwater Horizon Fire & Explosion – Breaking News
17. Rig blast survivor: ‘We had like zero time’
18. Oil rig blaze off Louisiana leaves at least 11 missing
19. Rescued oil rig explosion workers arrive to meet families at Kenner hotel
20. 11 missing in oil rig blast may not have escaped
21. Louisiana Oil Rig Explosion: Deep Water Horizon Workers Still Missing
22. Coast Guard confirms Horizon sinks
23. BP oil disaster: how a deadly methane bubble triggered explosion
24. Oil rig survivors recall a hiss before the blast
25. Oil slick spreads from sunken rig
26. ROV attempting to activate Deepwater Horizon Blowout Preventer
27. BP tries a new Gulf spill fix, as slick spreads
28. Engineers work to place siphon tube at oil spill site
29. Deepwater Horizon oil spill: Florida, Louisiana face worst disaster in US history (Video)
30. Gulf of Mexico response
31. Oil Slick Spreads off Gulf Coast