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The Well Control System or the Blowout Prevention System on a drilling rig is the system that prevents the uncontrolled, catastrophic release of high-pressure fluids (oil, gas, or salt water) from subsurface formations. These uncontrolled releases of formation fluids are referred to as Blowouts. Due to the explosive nature of oil and gas, any spark on the surface can result in the ignition of the fluids and an explosion on the rig. An explosive blowout and the failure of the Well Control System were the causes of the Mocondo Well disaster that killed eleven of the rig crew on the Deep Water Horizon Rig on April 20, 2010 and resulted in 35,000 to 60,000 bbl/day of crude oil to spill into the Gulf of Mexico. We will discuss this later in the lesson.

The blowout preventers are the principal piece of equipment in the well control system and are operated hydraulically; pressurized fluids are used to operate pistons and cylinders to open or close the valves on the BOP. The Accumulators (Item 18 in Figure 9.02) are used to store pressurized, non-explosive gas and pressurized hydraulic fluid to run the hydraulics systems on the rig. The accumulators store enough compressed energy to operate the blowout preventers even if the Power System of the rig is not operating.

The blowout preventer is a large system of valves each of which is capable of isolating the subsurface of the well from the rig to provide control over the well. These valves are typically stacked as shown in the Figure 9.11 and sit below the rig floor on land wells or some offshore wells; or they may sit on the seabed on other offshore wells.

In Figure 9.13, the blue area represents the doughnut-shaped bladder. As mentioned earlier, in the open position, (A), the drill pipe can be rotated or can be run up or down; while in the closed position, (B), the bladder pushes out, closing off the drill pipe, kelly, or open hole. The bladder based sealing element is not as effective as the ram type sealing elements; however, almost all blowout preventer stacks include at least one annular preventer.

A blowout begins as a Kick (entry of subsurface formation fluids into the wellbore). What distinguishes a kick from a blowout is that a kick can be controlled while a blowout is uncontrollable. We have already discussed two of the defenses against kicks when we discussed drilling fluids when we listed the objectives of the drilling fluid:

change in the apparent weight-on-bit (secondary indicator of a kick):If the weight-on-bit indicator in the rig’s Dog House shows a change in the weight-on-bit that is not explainable by the current drilling operations, then this may be an indication of a kick. The apparent weight-on-bit is affected by the buoyance caused by the wellbore fluid, which in turn, is affected by the density of the wellbore fluid. If a lighter formation fluid begins to replace the heavier, more dense drilling fluid, then an apparent increase in the weight-on-bit will occur.

reduction in the mud weight (secondary indicator of a kick):The Mud Man may observe a reduction or Cut in the mud density at the rig-site mud laboratory. This again may be an indication of a kick.

When a kick occurs, the Operating Company and Drilling Company always have well-specific plans in-place for all wells to ensure that any controllable kick does not turn into an uncontrollable blowout. I cannot go into the details of a well-specific procedures, but they will include some of the following features if a kick occurs during drilling operations:

Pick the drill bit off-bottom and Space Out (Spacing out refers to pulling the drill pipe out the hole so that the top connection – the thickest part of the drill string containing the threads and joints – is several feet above the rig floor. Spacing out ensures that the smaller diameter section of the drill string is inside the BOP, so that pipe rams can close and seat properly or blind rams or shear rams are opposite the smallest diameter section of steel. See Figure 9.15B)

So, we have discussed the role of drilling fluid to exert pressure on porous and permeable formations and to coat them with an impermeable filter cake to help prevent kicks from occurring. We have also discussed the role of the blowout preventer and company procedures to control a kick once one occurs. So, how do blowouts happen?

Perhaps you remember the Macondo Blowout (Deep Water Horizon Rig) disaster. The name Macondo was the Prospect name (remember, we discussed prospects and well proposals in a previous lesson) while the Deep Water Horizon was the name of the rig. This was the largest oil spill in the Gulf of Mexico. When the disaster occurred, eleven members of the rig crew were killed by the explosion when the natural gas ignited.

After learning about offshore drilling rigs, drilling crews, components of the drilling rig, kicks, and blowouts, I would highly recommend watching the movie “Deep Water Horizon” and use your knowledge about oil and gas well drilling to identify some of the technical aspects of the film. Ask yourselves some technical questions:

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The blast occurred on Wednesday at a remote site near Deanville, Texas, about 75 miles (120 km) east of Austin as contractors for Chesapeake Energy were using a workover rig, according to Sergeant Jimmy Morgan, a spokesman with the Texas Department of Public Safety. A workover involves re-entering a well to boost its production.

The fatality was the first in Texas involving a blowout since April 2013, when two Basic Energy Services workers were killed in West Texas, according to data from the Texas Railroad Commission, the state’s energy regulator. A blowout involves a sudden, high-pressure release of oil or gas from a well.

The number of workers in Texas injured during well blowouts has declined in recent years amid the rise in shale drilling. There were nine workers injured in blowouts last year, compared with 14 in 2017 and 21 in 2016, state data showed.

Blowout Preventers (BOPs) are a critical piece of safety equipment, as they protect rig crews, the rig, and the wellbore. Key maintains an inventory of

A blowout is the uncontrolled release of crude oil and/or natural gas from an oil well or gas well after pressure control systems have failed.blowout preventers intended to prevent such an occurrence. An accidental spark during a blowout can lead to a catastrophic oil or gas fire.

Gushers were an icon of oil exploration during the late 19th and early 20th centuries. During that era, the simple drilling techniques, such as cable-tool drilling, and the lack of blowout preventers meant that drillers could not control high-pressure reservoirs. When these high-pressure zones were breached, the oil or natural gas would travel up the well at a high rate, forcing out the drill string and creating a gusher. A well which began as a gusher was said to have "blown in": for instance, the Lakeview Gusher blew in in 1910. These uncapped wells could produce large amounts of oil, often shooting 200 feet (61 m) or higher into the air.gas gusher.

Despite being symbols of new-found wealth, gushers were dangerous and wasteful. They killed workmen involved in drilling, destroyed equipment, and coated the landscape with thousands of barrels of oil; additionally, the explosive concussion released by the well when it pierces an oil/gas reservoir has been responsible for a number of oilmen losing their hearing entirely; standing too near to the drilling rig at the moment it drills into the oil reservoir is extremely hazardous. The impact on wildlife is very hard to quantify, but can only be estimated to be mild in the most optimistic models—realistically, the ecological impact is estimated by scientists across the ideological spectrum to be severe, profound, and lasting.

The development of rotary drilling techniques where the density of the drilling fluid is sufficient to overcome the downhole pressure of a newly penetrated zone meant that gushers became avoidable. If however the fluid density was not adequate or fluids were lost to the formation, then there was still a significant risk of a well blowout.

In 1924 the first successful blowout preventer was brought to market.wellhead could be closed in the event of drilling into a high pressure zone, and the well fluids contained. Well control techniques could be used to regain control of the well. As the technology developed, blowout preventers became standard equipment, and gushers became a thing of the past.

In the modern petroleum industry, uncontrollable wells became known as blowouts and are comparatively rare. There has been significant improvement in technology, well control techniques, and personnel training which has helped to prevent their occurring.

A blowout in 1815 resulted from an attempt to drill for salt rather than for oil. Joseph Eichar and his team were digging west of the town of Wooster, Ohio, US along Killbuck Creek, when they struck oil. In a written retelling by Eichar"s daughter, Eleanor, the strike produced "a spontaneous outburst, which shot up high as the tops of the highest trees!"

The Shaw Gusher in Oil Springs, Ontario, was Canada"s first oil gusher. On January 16, 1862, it shot oil from over 60 metres (200 ft) below ground to above the treetops at a rate of 3,000 barrels (480 m3) per day, triggering the oil boom in Lambton County.

underwater blowout in U.S. history occurred on 20 April 2010, in the Gulf of Mexico at the Macondo Prospect oil field. The blowout caused the explosion of the Transocean and under lease to BP at the time of the blowout. While the exact volume of oil spilled is unknown, as of June 3, 2010United States Geological Survey Flow Rate Technical Group has placed the estimate at between 35,000 to 60,000 barrels (5,600 to 9,500 m3) of crude oil per day.

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights, and other organic compounds, found in geologic formations beneath the Earth"s surface. Because most hydrocarbons are lighter than rock or water, they often migrate upward and occasionally laterally through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as reservoirs) by impermeable rocks above. When hydrocarbons are concentrated in a trap, an oil field forms, from which the liquid can be extracted by drilling and pumping. The downhole pressure in the rock structures changes depending upon the depth and the characteristics of the source rock.Natural gas (mostly methane) may be present also, usually above the oil within the reservoir, but sometimes dissolved in the oil at reservoir pressure and temperature. Dissolved gas typically comes out of solution as free gas as the pressure is reduced either under controlled production operations or in a kick, or in an uncontrolled blowout. The hydrocarbon in some reservoirs may be essentially all natural gas.

The downhole fluid pressures are controlled in modern wells through the balancing of the hydrostatic pressure provided by the mud column. Should the balance of the drilling mud pressure be incorrect (i.e., the mud pressure gradient is less than the formation pore pressure gradient), then formation fluids (oil, natural gas, and/or water) can begin to flow into the wellbore and up the annulus (the space between the outside of the drill string and the wall of the open hole or the inside of the casing), and/or inside the drill pipe. This is commonly called a kick. Ideally, mechanical barriers such as blowout preventers (BOPs) can be closed to isolate the well while the hydrostatic balance is regained through circulation of fluids in the well. But if the well is not shut in (common term for the closing of the blow-out preventer), a kick can quickly escalate into a blowout when the formation fluids reach the surface, especially when the influx contains gas that expands rapidly with the reduced pressure as it flows up the wellbore, further decreasing the effective weight of the fluid.

Blowouts can eject the drill string out of the well, and the force of the escaping fluid can be strong enough to damage the drilling rig. In addition to oil, the output of a well blowout might include natural gas, water, drilling fluid, mud, sand, rocks, and other substances.

Blowouts will often be ignited from sparks from rocks being ejected, or simply from heat generated by friction. A well control company then will need to extinguish the well fire or cap the well, and replace the casing head and other surface equipment. If the flowing gas contains poisonous hydrogen sulfide, the oil operator might decide to ignite the stream to convert this to less hazardous substances.

Sometimes blowouts can be so forceful that they cannot be directly brought under control from the surface, particularly if there is so much energy in the flowing zone that it does not deplete significantly over time. In such cases, other wells (called relief wells) may be drilled to intersect the well or pocket, in order to allow kill-weight fluids to be introduced at depth. When first drilled in the 1930s relief wells were drilled to inject water into the main drill well hole.

The two main causes of a subsea blowout are equipment failures and imbalances with encountered subsurface reservoir pressure.Subsea wells have pressure control equipment located on the seabed or between the riser pipe and drilling platform. Blowout preventers (BOPs) are the primary safety devices designed to maintain control of geologically driven well pressures. They contain hydraulic-powered cut-off mechanisms to stop the flow of hydrocarbons in the event of a loss of well control.

Even with blowout prevention equipment and processes in place, operators must be prepared to respond to a blowout should one occur. Before drilling a well, a detailed well construction design plan, an Oil Spill Response Plan as well as a Well Containment Plan must be submitted, reviewed and approved by BSEE and is contingent upon access to adequate well containment resources in accordance to NTL 2010-N10.

An underground blowout is a special situation where fluids from high pressure zones flow uncontrolled to lower pressure zones within the wellbore. Usually this is from deeper higher pressure zones to shallower lower pressure formations. There may be no escaping fluid flow at the wellhead. However, the formation(s) receiving the influx can become overpressured, a possibility that future drilling plans in the vicinity must consider.

Myron M. Kinley was a pioneer in fighting oil well fires and blowouts. He developed many patents and designs for the tools and techniques of oil firefighting. His father, Karl T. Kinley, attempted to extinguish an oil well fire with the help of a massive explosion—a method still in common use for fighting oil fires. Myron and Karl Kinley first successfully used explosives to extinguish an oil well fire in 1913.

After the Macondo-1 blowout on the Deepwater Horizon, the offshore industry collaborated with government regulators to develop a framework to respond to future subsea incidents. As a result, all energy companies operating in the deep-water U.S. Gulf of Mexico must submit an OPA 90 required Oil Spill Response Plan with the addition of a Regional Containment Demonstration Plan prior to any drilling activity.

In order to regain control of a subsea well, the Responsible Party would first secure the safety of all personnel on board the rig and then begin a detailed evaluation of the incident site. Remotely operated underwater vehicles (ROVs) would be dispatched to inspect the condition of the wellhead, Blowout Preventer (BOP) and other subsea well equipment. The debris removal process would begin immediately to provide clear access for a capping stack.

Several not-for-profit organizations provide a solution to effectively contain a subsea blowout. HWCG LLC and Marine Well Containment Company operate within the U.S. Gulf of Mexico

On Sep. 30, 1966, the Soviet Union experienced blowouts on five natural gas wells in Urta-Bulak, an area about 80 kilometers from Bukhara, Uzbekistan. It was claimed in Komsomoloskaya Pravda that after years of burning uncontrollably they were able to stop them entirely.physics package into a 6-kilometre (20,000 ft) borehole drilled 25 to 50 metres (82 to 164 ft) away from the original (rapidly leaking) well. A nuclear explosive was deemed necessary because conventional explosives both lacked the necessary power and would also require a great deal more space underground. When the device was detonated, it crushed the original pipe that was carrying the gas from the deep reservoir to the surface and vitrified the surrounding rock. This caused the leak and fire at the surface to cease within approximately one minute of the explosion, and proved to be a permanent solution. An attempt on a similar well was not as successful. Other tests were for such experiments as oil extraction enhancement (Stavropol, 1969) and the creation of gas storage reservoirs (Orenburg, 1970).

Walsh, Bryan (2010-05-19). "Gulf Oil Spill: Scientists Escalate Environmental Warnings". Time. Archived from the original on June 29, 2010. Retrieved June 30, 2010.

Whipple, Tom (2005-03-15). "Full steam ahead for BC offshore oil drilling". Energybulletin.net. Archived from the original on 2008-01-20. Retrieved 2016-01-30.

"East Texas Oil Museum at Kilgore College – History". Easttexasoilmuseum.com. 1930-10-03. Archived from the original on 2016-02-08. Retrieved 2016-01-30.

Norris Mcwhirter; Donald McFarlan (1989). the Guinness Book of Records 1990. Guinness Publishing Ltd. ISBN 978-0-85112-341-7. Archived from the original on 2018-05-03.

Christopher Pala (2001-10-23). "Kazakhstan Field"s Riches Come With a Price". Vol. 82, no. 715. The St. Petersburg Times. Archived from the original on 2013-12-28. Retrieved 2009-10-12.

"NTL No. 2010-N10". BSEE.gov. US Department of the Interior Bureau of Ocean Energy Management, Regulation and Enforcement. Archived from the original on 2015-09-30.

Madrid, Mauricio; Matson, Anthony (2014). "How Offshore Capping Stacks Work" (PDF). Society of Petroleum Engineers: The Way Ahead. 10 (1). Archived (PDF) from the original on 2015-11-29.

CineGraphic (4 July 2009). "An Atomic Bomb will stop the Gulf Oil Leak, LOOK!". Archived from the original on 7 November 2017. Retrieved 3 May 2018 – via YouTube.

Welcome to Pickett Oilfield’s Blowout Preventers web page. Blowout Preventers otherwise called BOP’s are devices that are used in the drilling industry to seal off and control oil and gas wells. BOP’s are designed to prevent “blowout” which is the unconstrained discharge of oil or gas from the well being drilled. These Preventers are large valves that withstand high pressure in order to safely, and often times remotely, inhibit the uncontrolled release of liquids from the well during operation. Moreover, they are usually installed in stacks and are the second line of defense to safeguard the well and employees.

Our company has been in the oil & gas drilling equipment industry for over 38 years, supplying new and used Blowout Preventers and pressure control equipment to customers in practically every producing region in the world. We are here to serve all your drilling equipment needs – if you don’t see it on this site, just give us a call or email. We can get it, if you need it!

Pickett Oilfield, LLC offers prospective buyers an extensive selection of quality new and used oil & gas drilling equipment, including Blowout Preventers to choose from at competitive prices. Browse our inventory of Preventers and BOP parts for sale at competitive rates.

Welcome to Pickett Oilfield’s Blowout Preventers web page. Blowout Preventers otherwise called BOP’s are devices that are used in the drilling industry to seal off and control oil and gas wells. BOP’s are designed to prevent “blowout” which is the unconstrained discharge of oil or gas from the well being drilled. These Preventers are large valves that withstand high pressure in order to safely, and often times remotely, inhibit the uncontrolled release of liquids from the well during operation. Moreover, they are usually installed in stacks and are the second line of defense to safeguard the well and employees.

Our company has been in the oil & gas drilling equipment industry for over 38 years, supplying new and used Blowout Preventers and pressure control equipment to customers in practically every producing region in the world. We are here to serve all your drilling equipment needs – if you don’t see it on this site, just give us a call or email. We can get it, if you need it!

Pickett Oilfield, LLC offers prospective buyers an extensive selection of quality new and used oil & gas drilling equipment, including Blowout Preventers to choose from at competitive prices. Browse our inventory of Preventers and BOP parts for sale at competitive rates.

PickettOilfield.com offers prospective buyers an extensive selection of quality new and used oilfield equipment, including blowout preventers and pressure control equipment to choose from at competitive prices. For more information or to request a quote contact us by phone at 936-336-5154 or by email at sales@pickettoilfield.com

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Summary Finding 2.1: The flow of hydrocarbons that led to the blowout of the Macondo well began when drilling mud was displaced by seawater during the temporary abandonment process.

Summary Finding 2.2: The decision to proceed to displacement of the drilling mud by seawater was made despite a failure to demonstrate the integrity of the cement job even after multiple negative pressure tests. This was but one of a series of questionable decisions in the days preceding the blowout that had the effect of reducing the margins of safety and that evidenced a lack of safety-driven decision making.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Finding 2.6: Evidence available before the blowout indicated that the flapper valves in the float collar probably failed to seal, but this evidence was not acted on at the time.

Finding 2.10: Although data were being transmitted to shore, it appears that no one in authority (from BP onshore management or a regulatory agency) was required to examine test results and other critical data and render an opinion to the personnel on the rig before operations could continue.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Observation 2.5: Had the path of the blowout been up the annulus, a liner top or the rupture discs could have failed and allowed flow to escape the well into a shallow formation. This would result in a downhole blowout that could breach at the seafloor under the correct conditions. Future well construction could avoid this possibility by running one of the deeper casing strings back to the wellhead where it can be sealed. For example, in this well the 13 ⅝-inch liner could have been run back to the wellhead. This would protect the shallower liner tops and rupture discs from potential exposure to high pressure from flow up the annulus from a deeper reservoir.

Recommendation 2.2: During drilling, rig personnel should maintain a reasonable margin of safety between the equivalent circulating density and the density that will cause wellbore fracturing.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Finding 3.2: The crew did not realize that the well was flowing until mud actually exited and was expelled out of the riser by the flow at 21:40. Early detection and control of flow from a reservoir are critical if an impending blowout is to be prevented by a BOP whose use against a full-flowing well is untested.

Finding 3.3: Once mud began to flow above the rig floor, the crew attempted to close the upper annular preventer of the BOP system, but it did not seal properly. The BOP system had been used in the month previously to strip 48 tool joints, and apparently it was untested for integrity afterwards. Annulars are often unable to seal properly after stripping. In addition, the flowing pressure inside the well may have been larger than the preset annular closing pressure could overcome. What tests of sealing against flow have been done on this design of annular are unknown.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Finding 3.4: The crew also closed the VBRs. The damaged pipe under the upper annular demonstrated its failure to seal, and the well was only sealed, resulting in the final pressure spike, when these VBRs were closed. The DNV investigation also found that these rams closed, and they could only be closed by command from the rig control panels and not by an ROV. At this point the flow from below the VBRs would have been closed off, but gas and oil had already flowed into the marine riser above the BOP system and continued to rise to the surface, where the gas exploded.

Finding 3.6: Once the fire started on the rig, an attempt was made (after 7 minutes) to activate the EDS, which should have closed the BSR and disconnected the LMRP. This appears to have failed because the MUX communication cables were destroyed by the explosion or fire.

Finding 3.7: Once hydraulic and electrical connection with the rig was lost at the BOP, the AMF should have activated the BSR. It might have failed at this time because of a low battery charge in one control pod and a mis-wired solenoid valve in the other, but both these points are in dispute. However, no short-term reduction in hydrocarbon flow from the well was observed after the initial fire and explosion. Such a reduction would necessarily have resulted from the VBRs sealing the annulus in the BOP and the failed BSR shearing action effectively choking, at least for a brief period of time, virtually the entire cross section of the 5½-inch drill string. Viewed in total, the evidence appears more supportive of the autoshear activation of the BSR.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Finding 3.15: Unfortunately, even if the BSR had functioned after being activated by the EDS or the AMF, it would not likely have prevented the initial explosions, fire, and resulting loss of life, because hydrocarbons had already flowed into the marine riser above the BOP system. If the BOP system had been able to seal the well, the rig might not have sunk, and the resulting oil spill would likely have been minimized.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Finding 3.17: Regulations in effect before the incident required the periodic testing of the BOP system. However, they did not require testing under conditions that simulated the hydrostatic pressure at the depth of the BOP system or under the condition of pipe loading that actually occurred under dynamic flow, with the possible entrained formation rock, sand, and cement, and no such tests were run. Furthermore, because of the inadequate monitoring technology, the condition of the subsea control pods at the time of the blowout was unknown.

2. While individual subsystems of various BOP designs have been studied on an ad hoc basis over the years, the committee could find no evidence of a reliability assessment of the entire BOP system, which would have included functioning at depth under precisely the conditions of a dynamic well blowout. Furthermore, the committee could find no publicly available design criteria for BOP reliability.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Finding 3.21: When a signal is sent from the drilling rig to the BOP (on the seafloor) to execute a command, the BOP sends a message back that the signal has been received. However, there are no transducers that detect the position or status of key components, and there are no devices to send a signal that any command has been executed (such as pressure or displacement sensors confirming that the hydraulics have been actuated, that rams have moved, or that pipe has been cut). Furthermore, there are no sensors to communicate flow or pressures in the BOP to the rig floor.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Summary Recommendation 3.1: BOP systems should be redesigned to provide robust and reliable cutting, sealing, and separation capabilities for the drilling environment to which they are being applied and under all foreseeable operating conditions of the rig on which they are installed. Test and maintenance procedures should be established to ensure operability and reliability appropriate to their environment of application. Furthermore, advances in BOP technology should be evaluated from the perspective of overall system safety. Operator training for emergency BOP operation should be improved to the point that the full capabilities of a more reliable BOP can be competently and correctly employed when needed in the future.

Summary Recommendation 3.5: Instrumentation and expert system decision aids should be used to provide timely warning of loss of well control to drillers on the rig (and ideally to onshore drilling monitors as well). If the warning is inhibited or not addressed in an appropriate time interval, autonomous operation of the BSRs, EDS, general alarm, and other safety systems on the rig should occur.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Recommendation 3.8: A reliable and effective EDS is needed to complete the three-part objective of cutting, sealing, and separating as a true “dead man” operation when communication with the rig is lost. The operation should not depend on manual intervention from the rig, as was the case with the Deepwater Horizon. The components used to implement this recommendation should be monitored or tested as necessary to ensure their operation when needed.

Finding 4.1b: The rig was not designed to prevent explosion or fire once it was surrounded by the extent of combustible atmosphere facing the Deepwater Horizon.

Finding 4.1c: Hydrocarbon flow was not redirected overboard. Overboard discharge of the blowout might have delayed the explosion and fire aboard the rig.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Finding 4.2a: The rig’s dynamic positioning system operated as designed until the loss of power disabled the rig’s ability to maintain station or reposition under control.

Finding 4.3: Alarm and indication systems, procedures, and training were insufficient to ensure timely and effective actions to prevent the explosions or respond to save the rig.

Finding 4.3a: The rig design did not employ automatic methods to react to indications of a massive blowout, leaving reactions entirely in the hands of the surviving crew.

Finding 4.3e: The training routine did not include any full rig drills designed to develop and maintain crew proficiency in reacting to major incidents.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Finding 4.3g: Crew members lacked cross-rate training to understand rig total systems and components. As a result, many of the crew were inadequately prepared to react to the incident.

Finding 4.4: Confusion existed about decision authority and command. Uncertainty as to whether the rig was under way or moored to the wellhead contributed to the confusion on the bridge and may have impaired timely disconnect.

Finding 4.5: The U.S. Coast Guard’s requirement for the number and placement of lifeboats was shown to be prudent and resulted in sufficient lifeboat capacity for effective rig abandonment. The Coast Guard’s investigation report (USCG 2011) notes a lack of heat shielding to protect escape paths and life-saving equipment.

Finding 4.6: The above findings indicate that the lack of fail-safe design and testing, training, and operating practices aboard the rig contributed to loss of the rig and loss of life. The chain of events that began downhole could have been interrupted at many points, such as at the wellhead by the BOP or aboard the rig, where the flow might have been directed overboard or where the rig itself might have been disconnected from the well and repositioned. Had the rig been able to disconnect, the primary fuel load for the fire would have been eliminated.

Observation 4.1: The actions of some crew members in requiring due consideration of additional survivors before launching lifeboats, despite the fearsome fires engulfing the rig, are commendable and were important in the highly successful evacuation.

Observation 4.3: Conditions of explosion, fire, loss of lighting, toxic gas, and eventual flooding and sinking could have resulted in many more injuries or deaths if not for the execution of the rig"s evacuation.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Summary Recommendation 4.1: Instrumentation and expert system decision aids should be used to provide timely warning of loss of well control to drillers on the rig (and ideally to onshore drilling monitors as well). If the warning is inhibited or not addressed in an appropriate time interval, autonomous operation of the BSRs, EDS, general alarm, and other safety systems on the rig should occur.

Recommendation 4.2: Rigs should be designed so that their instrumentation, expert system decision aids, and safety systems are robust and highly reliable under all foreseeable normal and extreme operating conditions. The design should account for hazards that may result from drilling operations and attachment to an uncontrolled well. The aggregate effects of cascading casualties and failures should be considered to avoid the coupling of failure modes to the maximum reasonable extent.

Recommendation 4.3: Industry and regulators should develop fail-safe design requirements for the combined systems of rig, riser, BOP, drilling equipment, and well to ensure that (a) blowouts are prevented and (b) if a blowout should occur the hydrocarbon flow will be quickly isolated and the rig can disconnect and reposition. The criteria for these requirements should be maximum reasonable assurance of (a) and (b) and successful crew evacuation under both scenarios.

Recommendation 4.4: Industry and regulators should implement a method of design review for systemic risks for future well design that uses a framework with attributes similar to those of the Department of Defense Standard Practice for System Safety (DoD 2000), which articulates standard practices for system safety for the U.S. military, to address the complex and integrated “system of systems” challenges faced in safely operating deepwater drilling rigs. The method should take into consideration the coupled effects of well design and rig design.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Recommendation 4.12: Drilling rig contractors should require realistic and effective training in operations and emergency situations for key personnel before assignment to any rig. Industry should also require that personnel aboard the rig achieve and maintain a high degree of expertise in their assigned watch station, including formal qualification and periodic reexamination.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Recommendation 4.15: Regulators should require that all permanent crew on a rig achieve a basic level of qualification in damage control and escape systems to ensure that all hands are able to contribute to resolving a major casualty.

Recommendation 4.21: Industry and regulators should develop and implement a certification to ensure that design requirements, material condition, maintenance, modernization, operating and emergency instructions, manning, and training are all effective in meeting the requirements of Recommendation 4.3 throughout the rig’s service life.

Recommendation 4.22: Regulators should require that the rig, the entire system, and the crew be examined annually by an experienced and objective outside team to achieve and maintain certification in operational drilling safeguards. The consequence of unsatisfactory findings should be suspension of the crew’s operation except under special supervisory conditions.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Summary Finding 5.1: The actions, policies, and procedures of the corporations involved did not provide an effective system safety approach commensurate with the risks of the Macondo well. The lack of a strong safety culture resulting from a deficient overall systems approach to safety is evident in the multiple flawed decisions that led to the blowout. Industrial management involved with the Macondo well–Deepwater Horizon disaster failed to appreciate or plan for the safety challenges presented by the Macondo well.

Observation 5.4: The operating leaseholder company is the only entity involved in offshore drilling that is positioned to manage the overall system safety of well drilling and rig operations.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Summary Recommendation 5.1: Operating companies should have ultimate responsibility and accountability for well integrity, because only they are in a position to have visibility into all its aspects. Operating companies should be held responsible and accountable for well design, well construction, and the suitability of the rig and associated safety equipment. Notwithstanding the above, the drilling contractor should be held responsible and accountable for the operation and safety of the offshore equipment.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Recommendation 5.3b: In addition to rig personnel, onshore personnel involved in overseeing or supporting rig-based operations should have sufficient understanding of the fundamental processes and risks involved.

Recommendation 5.3c: A research process is needed for establishing standardized requirements for education, training, and certification of everyone working on an offshore drilling rig. Additional standardized requirements should be established for education, training, and certification of key drilling-related personnel working offshore and onshore.

Recommendation 5.5b: Effective response to a crisis situation requires teamwork to share information and perform actions. Training should involve on-site team exercises to develop competent decision making, coordination, and communication. Emergency team drills should involve full participation, as would be required in actual emergency situations, including a well blowout. Companies should approach team training as a means of instilling overall safety as a high priority.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Summary Recommendation 5.6: Efforts to reduce the probability of future blowouts should be complemented by capabilities of mitigating the consequences of a loss of well control. Industry should ensure timely access to demonstrated well-capping and containment capabilities.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Recommendation 6.10: BSEE should review existing codes and standards to determine which should be improved regarding requirements for (a) use of state-of-the-art technologies, especially in areas related to well construction, cementing, BOP functionality, and alarm and evacuation systems, among others, and (b) approval and certification incumbent to management of changes in original plans for well construction.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

should be held responsible and accountable for well design, well construction, and the suitability of the rig and associated safety equipment. Notwithstanding the above, the drilling contractor should be held responsible and accountable for the operation and safety of the offshore equipment.

DNV. 2011a. Forensic Examination of Deepwater Horizon Blowout Preventer, Vols. 1 and 2 (Appendices). Final Report for U. S. Department of the Interior, Bureau of Ocean Energy Management, Regulation, and Enforcement, Washington, D.C. Re-

Suggested Citation:"Appendix C: Findings, Observations, and Recommendations." National Academy of Engineering and National Research Council. 2012. Macondo Well Deepwater Horizon Blowout: Lessons for Improving Offshore Drilling Safety. Washington, DC: The National Academies Press. doi: 10.17226/13273.

DNV. 2011b. Addendum to Final Report: Forensic Examination of Deepwater Horizon Blowout Preventer. Report No. EP030842. http://www.boemre.gov/pdfs/maps/AddendumFinal.pdf. Most recently accessed Jan. 17, 2012.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

In response to your request, the National Academy of Engineering (NAE) and the National Research Council (NRC) formed a committee to examine the causes of the Deepwater Horizon mobile offshore drilling unit (MODU)–Macondo well blowout, explosion, fire, and oil spill that occurred on April 20, 2010, and to identify measures for preventing similar incidents in the future. The committee membership includes NAE members and other similarly qualified practitioners and academicians who bring a broad spectrum of expertise, including the areas of geophysics, petroleum engineering, marine systems, accident and incident investigations, safety systems, risk analysis, human factors, and organizational behavior (see Appendix A). This letter constitutes the interim letter report required in the committee’s statement of task (see Appendix B).

To inform its deliberations, the committee obtained information from a variety of sources. It heard presentations from representatives of government and private organizations, observed hearings conducted by the Marine Board of Inquiry (MBI),1 made site visits, and assessed written information (see Appendix C). At the time the committee completed its deliberations for this report, it had not been able to examine the blowout preventer (BOP) that was part of the drilling operation at the Macondo well nor to interview representatives of Cameron (manufacturer of the recovered BOP) or Transocean [owner and operator of the Deepwater Horizon mobile offshore drilling unit (MODU)]. Also, the committee only recently received requested technical drilling data, which are still being analyzed. Therefore, the committee’s information-gathering activities and deliberations concerning the probable causes of the Deepwater Horizon incident will continue beyond this interim report.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

The committee notes that, at this time, multiple theories and factors have been proffered with regard to the specific failure mechanism and hydrocarbon pathway that led to the blowout of the Macondo well. Most of the theories and factors have in common issues regarding the effectiveness of cementing the long-string production casing to prepare the well for temporary abandonment.

The committee further notes that it may not be possible to definitively establish the precise failure mechanism and hydrocarbon pathway that led to the blowout of the well, given the tragic loss of 11 witnesses, the sinking of the rig along with important operating records, and the general difficulty in obtaining reliable forensic information at the depth of the Macondo well. In addition, no information is available yet from the detailed examination of the recovered BOP. Nonetheless, in preparing this report, the committee believes it has been able to develop a good understanding of a number of key factors and decisions that may have contributed to the blowout of the well, including engineering, testing, and maintenance procedures; operational oversight; regulatory procedures; and personnel training and certification. It is important to note that the findings and observations in this interim report are preliminary and serve to identify areas of concern that will be pursued in greater detail in the final report. The committee will also consider government and private-sector initiatives recently developed for deepwater exploration in the United States. Therefore, the committee does not present recommendations at this time. As indicated in the committee’s statement of task, this interim consensus report is provided to inform the ongoing activities of the MBI, the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling2 and other formal investigations.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

The bottom section of the casing in the Macondo well, called the “shoe track,” was a section of casing about 189 ft long with a reamer-guide shoe at the bottom and a dual-flapper float collar on top.22 This section of casing is meant to contain the last, or “tail,” cement that is pumped—in this case unfoamed cement. The float collar flappers are designed to close after the cement is in place (and starts setting up) to prevent any flow back into the casing (and up the well) caused by hydrostatic pressure differences between the dense cement and drilling mud on the outside of the casing and the less dense displacement fluid on the inside. The float collar also acts as the landing point for the cementing plugs used during the job. The float collar used employed a differential fill tube that allowed mud to flow into the casing as it was run into the well. The fill tube in this case was designed to be pumped out of the float collar if the pump rate was higher than 5 barrels per minute. The top of the float collar in this well was at a depth of 18,115 ft measured from the rig floor. This placed the float collar above the base of the productive reservoir. The potential impacts of the location of the float collar will be evaluated by the committee, including whether it potentially precluded full evaluation of the cement job by logging. The committee will also consider available information related to the differential pressure to close the float collar flappers, the utility and the removal of the fill tube from the float collar, the utility of a float shoe rather than a guide shoe, and the possible fate of the cement placed in the shoe track.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

Findings 1 and 3 in the BP Deepwater Horizon Accident Investigation Report23 are, respectively, “The annulus cement barrier did not isolate the hydrocarbons” and “The negative-pressure test was accepted although well integrity had not been established.” Proceeding to displace the dense drilling mud in the riser without an effective cement barrier was followed by the entry of hydrocarbons into the well and the eventual blowout and explosion.

There were several clear failures in the monitoring of the Macondo well that appear to have ultimately contributed to the blowout and explosion on the Deepwater Horizon MODU. Because detection of hydrocarbons, especially gas entering a well, is critical for maintaining safe operations, this report focuses on monitoring failures immediately prior to the first explosion on April 20, 2010. The possibility of hydrocarbons entering a well has such important implications for safety that it is common practice for the mud-logging company, drilling contractor, and operator to focus on determining whether this is occurring to ensure that remedial action can be taken immediately.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

When hydrocarbon flow was finally noted, the Deepwater Horizon crew diverted the flow to the mud-gas separator. This resulted in gas exiting the vents located on the derrick, directly above the rig floor. It is unknown why personnel did not choose to divert the gas directly overboard.

The BOP is relied on as a critical component for preventing uncontrolled hydrocarbon flows and avoiding a catastrophic blowout of a well. Various attempts were made to activate BOP functions on the Deepwater Horizon MODU, and there are indications that one of the annular preventers and perhaps a variable bore ram did operate to some degree, once actuated. These operations failed to control the flow, however. Furthermore, the blind shear ram (BSR), which was intended to shear the drill pipe and the production casing and seal the well bore in an emergency, was unable to recapture control, even after the explosion when hot stab procedures were initiated via remotely operated vehicle.

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

The committee will pay particular attention to the design, test, and maintenance of the automatic mode function (designed to activate the BSR upon loss of hydraulic pressure and electric power from the rig) and of the emergency disconnect system that is intended to separate the lower marine riser from the rest of the BOP.

The Deepwater Horizon MODU, built in 2001, was a semisubmersible, dynamically positioned vessel designed for deepwater drilling. Once the uncontrolled flow of hydrocarbons had enveloped the deck of the rig on April 20, ignition was most likely, given the large volume of gas, the multitude of ignition sources on the rig, moderate temperature, and limited wind conditions. Testimony provided at the MBI hearings indicated, however, that various alarms and safety systems on the rig failed to operate as intended, potentially affecting the time available for personnel to evacuate.

Combustible gas detectors on the rig were designed to automatically activate visual and auditory alarms when monitored gas concentrations exceeded a predetermined level of safety. Some of those detectors were designed to activate systems that automatically closed dampers and shut down fans to prevent ambient gas flow into specific zones on the rig. Similar kinds of emergency closures and shutdowns on other parts of the rig required manual activation in response to a combustible gas detector alarm. According to MBI testimony, inspectors working on behalf of the U.S. Coast Guard and MMS verified that components of the rig’s safety systems were in place and functioning properly.30 Rig personnel testified, however, that several fire and gas detectors were not functioning or had been inhibited because of frequent false alarms.31 In an inhibited mode, automatic systems would display an alert on one or more control panels upon detection of high levels of gas; subsequent responses would require manual activation. Testimony also indicated that although systems were in place to determine the operating status of individual gas detectors and alarms, there was no procedure for tracking the status of all alarms on the rig.32

Engines on the rig were equipped with devices designed to shut them down automatically when predetermined overspeed conditions occurred. It was reported that the air intake controls for the engine room on the rig were not set up to automatically close upon detection of high concentrations of gas. According to testimony, at least one engine on the vessel appeared to speed up excessively prior to the first explosion.33 At this time, the

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such Events. Washington, DC: The National Academies Press. doi: 10.17226/13047.

During the course of its study, the committee will examine evidence on the maintenance, testing, operating procedures, and reliability of alarms and other safety systems on the Deepwater Horizon MODU. It will also assess the adequacy of such systems given the hazards present on such vessels and the need to provide adequate time for emergency response by rig personnel.

Witnesses at the MBI hearings exhibited a variety of perspectives with regard to the assignment of responsibility aboard the Deepwater Horizon MODU. Testimony suggested that decision making was a “team process” involving personnel from various companies, or that the offshore installation manager (OIM) and/or the well site leader (“company man”) were responsible for individual decisions.34 Also, concern was expressed by rig personnel regarding the change in well site leader just prior to critical temporary abandonment procedures.35 A lack of specific identification of authority appears in testimony regarding the involvement of shore-based personnel. The decision to accept the results of the negative-pressure test as satisfactory—rationalized as being the result of some hypothesized “bladder effect” (or annular compression)36—without review by adequately trained shore-based engineering or management personnel37 suggests a lack of onboard expertise and of clearly defined responsibilities and the associated limitations of authority. Similarly, the decision to disregard the OptiCemTM modeling

Suggested Citation:"Letter Report." National Academy of Engineering and National Research Council. 2010. Interim Report on Causes of the Deepwater Horizon Oil Rig Blowout and Ways to Prevent Such