OIL AND GAS

Interior Has 

Strengthened Its 

Oversight of Subsea 

Well Containment, but 

Should Improve Its 

Documentation

Report to Congressional Requesters

February 2012

GAO-12-244

United States Government Accountability Office

GAO
United States Government Accountability Office

Highlights of GAO-12-244, a report to 

congressional requesters

February 2012

OIL AND GAS

Interior Has Strengthened Its Oversight of Subsea 

Well Containment, but Should Improve Its 

Documentation 

Why GAO Did This Study

On April 20, 2010, an explosion and 

fire on board the Deepwater Horizon, 

an offshore drilling rig, resulted in 11

deaths and the largest oil spill in U.S. 

history in the Gulf of Mexico. After this 

event, the Department of the Interior

(Interior), which oversees oil and gas 

operations in federal waters, 

suspended certain offshore drilling 

operations. After developing new 

guidance, Interior resumed approving

drilling operations in the Gulf of 

Mexico. GAO was asked to examine 

(1) the industry’s improved capabilities 

for containing subsea wells (those on 

the ocean floor) in the Gulf of Mexico; 

(2) Interior’s oversight of subsea well 

containment in the Gulf of Mexico; and 

(3) the potential to use similar subsea 

well containment capabilities in other 

federal waters, such as those along the 

Alaskan coast.

GAO reviewed laws, regulations, and 

guidance; documents from oil and gas 

operators; and Interior’s oversight

processes. GAO also interviewed 

agency officials and industry 

representatives. 

What GAO Recommends

To help ensure that operators can 

respond effectively to a subsea well 

blowout, GAO recommends that 

Interior document a time frame for 

incorporating well containment 

response scenarios into unannounced 

spill drills. In commenting on a draft of 

this report, Interior concurred with 

GAO’s recommendation.

What GAO Found

Since the Deepwater Horizon incident, the oil and gas industry has improved its 

capabilities to respond to a subsea well blowout—the uncontrolled release of oil 

or gas from a well on the ocean floor—in the Gulf of Mexico. In particular, 

operators have formed two new not-for-profit organizations that can quickly make 

available well containment equipment, services, and expertise. Among the

equipment that these organizations can provide are capping stacks—devices 

used to stop the flow of oil or gas from a well. This improved well containment 

response equipment consists primarily of existing technologies that have been 

modified to support well containment, according to industry representatives. 

Following the Deepwater Horizon incident, Interior strengthened its review plans 

and resources to contain a subsea well blowout; however, its internal oversight 

processes have not yet been fully documented. Interior has issued guidance to 

operators outlining information that must be provided to Interior to demonstrate 

that operators can respond to a well blowout. Interior officials said that they 

expect to have documentation of their process for reviewing this information in 

place by spring 2012. Also, Interior incorporated tests of an operator’s well 

containment response capabilities into two unannounced spill drills, and Interior 

officials told us they intend to incorporate such tests into future spill drills. 

However, Interior has not documented a time frame for incorporating these tests, 

and until it does so there is limited assurance of an operator’s ability to respond 

to a subsea well blowout. 

Subsea well containment capabilities developed for the Gulf of Mexico could 

generally be used elsewhere, including Alaskan waters, according to industry 

representatives and Interior officials. However, because other areas lack the

infrastructure and equipment present in the Gulf of Mexico, well blowout 

response capabilities are more limited. Two operators have submitted plans to 

Interior to drill in waters north of Alaska as early as the summer of 2012. They 

are developing, but have not submitted, final well containment plans to Interior, 

and these plans will need to be approved by Interior before drilling. Oil and gas 

exploration and production off the coast of Alaska is likely to encounter 

environmental and logistical risks that differ from those in the Gulf of Mexico 

because of the region’s cold and icy conditions—factors that would also likely 

affect the response to a well blowout. 

A Capping Stack Ready for Deployment

View GAO-12-244. For more information, 

contact Madhav Panwar at (202) 512-6228 or 

panwarm@gao.gov or Frank Rusco at (202) 

512-3841 or ruscof@gao.gov. 
Page i GAO-12-244 Subsea Well Containment

Letter 1 

Background 3

Industry Has Improved Its Capabilities for Subsea Well 

Containment in the Gulf of Mexico 9

Interior Has Issued New Guidance and Is Documenting Many of Its 

Oversight Processes, but Has Not Documented a Time Frame for 

Testing Operators’ Responses to a Subsea Blowout 16

Subsea Well Containment Capabilities Available for the Gulf of 

Mexico Could Be Used in Other Federal Waters, but 

Environmental and Logistical Risks Differ 20

Conclusions 25

Recommendation for Executive Action 26

Agency Comments and Our Evaluation 26

Appendix I Supplemental Information on Typical Components of Well

Containment Plans 28

Appendix II Comments from the Department of the Interior 32

Appendix III GAO Contacts and Staff Acknowledgments 34

Table

Table 1: Capping Stacks Developed by the Oil Industry 29

Figures

Figure 1: Key Equipment Used during the Drilling Phase 7

Figure 2: Subsea Well Containment Response Equipment 13

Figure 3: A Capping Stack Ready for Deployment 15

Figure 4: The Beaufort and Chukchi Seas off the Coast of Alaska 22

Contents
Page ii GAO-12-244 Subsea Well Containment

Abbreviations

BOEM Bureau of Ocean Energy Management

BOEMRE Bureau of Ocean Energy Management, Regulation and 

 Enforcement

BSEE Bureau of Safety and Environmental Enforcement

EPA Environmental Production Agency

HWCG Helix Well Containment Group

MMPA Marine Mammal Protection Act

MWCC Marine Well Containment Company

ONRR Office of Natural Resources and Revenue

psig pounds per square inch

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without further permission from GAO. However, because this work may contain 

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Page 1 GAO-12-244 Subsea Well Containment

United States Government Accountability Office

Washington, DC 20548

February 29, 2012

The Honorable Henry A. Waxman

Ranking Member

Committee on Energy and Commerce

House of Representatives

The Honorable Edward J. Markey

Ranking Member

Committee on Natural Resources 

House of Representatives

On April 20, 2010, the Deepwater Horizon offshore drilling rig exploded 

and caught on fire, resulting in 11 deaths, serious injuries, and the largest 

marine oil spill in the history of the United States. Located over 40 miles 

off the coast of Louisiana and at a depth of nearly 5,000 feet in the Gulf of 

Mexico, the subsea well spilled oil for 87 days before responders were 

able to cap the well and contain the flow of oil. According to government 

estimates, by that time, over 4.9 million barrels of oil had spilled into the 

Gulf of Mexico. The spill damaged the environment and adversely 

affected oil workers and nearby businesses, with estimated costs to 

compensate for these damages totaling in the billions of dollars.

The nation’s economy and security are heavily dependent on oil and 

natural gas.1

 

1

Petroleum exists in both liquid and gaseous forms. Throughout this report, we refer to the 

liquid forms as “oil” and the gaseous forms as “gas.”

The Department of the Interior (Interior) regulates oil and 

gas activities in federal waters, including in the Gulf of Mexico. According 

to a 2010 Interior study, almost 97 percent of U.S. offshore oil and gas 

activity in federal waters occurs there. However, drilling for oil and gas is 

an inherently risky undertaking, and although industry has the capability 

to respond to subsea blowouts—the uncontrolled release of oil or gas 

from a well on the ocean floor— the risk of the loss of control of a subsea 

well can never be entirely eliminated. Given this risk––and the severity of 

the consequences––it is critical that the operators who lease public lands 

and the federal agency that oversees them demonstrate that they are 

taking all reasonable steps to mitigate these risks. Following the 

Deepwater Horizon incident, for example, Interior suspended certain 

 
 

Page 2 GAO-12-244 Subsea Well Containment

offshore drilling operations and developed new regulations and guidance 

for oil and gas operators. Interior lifted this moratorium on October 12, 

2010, and on February 28, 2011, issued its first permit for offshore drilling 

under the new guidance.

In this context, you asked us to examine Interior’s approach to addressing 

the risk of subsea well blowouts and oversight of industries’ well 

containment capabilities.2

To examine subsea well containment capabilities, we reviewed technical 

documents that the two well containment organizations that operate in the 

Gulf of Mexico provided to Interior and visited facilities, both in the United 

States and in the United Kingdom, where certain well containment 

equipment was stored, displayed, or tested. In addition, we also 

interviewed Interior officials to identify the capabilities used to support 

new applications to drill. We also interviewed representatives of the two 

well containment organizations to identify capping and containment 

capabilities and learn how they would deploy and operate these 

capabilities in a subsea well blowout.

Our objectives were to examine (1) 

improvements to subsea well containment capabilities now available for 

use in the Gulf of Mexico; (2) Interior’s oversight of subsea well 

containment in the Gulf of Mexico following the Deepwater Horizon

incident; and (3) the potential to use similar subsea well containment 

capabilities in other federal waters, such as those off the Alaskan coast.

3

 

2

“Well containment” refers to measures taken after an event such as a blowout to regain 

control of the well and capture any released oil. 

For the purposes of this report, we 

focused on capacities for subsea well containment and did not review 

surface oil spill response capabilities, such as booms, which are floating 

barriers serving to contain an oil spill, or oil skimmers, which are devices 

that separate oil from water. To examine Interior’s oversight of subsea 

well containment, we reviewed laws, regulations, and current guidance 

that pertain to subsea well control and interviewed agency officials 

responsible for reviewing and approving well containment plans. We 

reviewed a nonprobability sample of 7 well containment plans from the 

over 30 that had been approved by Interior as of August 2011 

representing different well characteristics to further understand the 

3

The Marine Well Containment Company and the Helix Well Containment Group were the 

two organizations formed after the Deepwater Horizon incident to offer well containment 

services in the Gulf of Mexico.
 

Page 3 GAO-12-244 Subsea Well Containment

capabilities and plans for capping and containment.4

We conducted this performance audit from April 2011 to January 2012, in 

accordance with generally accepted government auditing standards. 

Those standards require that we plan and perform the audit to obtain 

sufficient, appropriate evidence to provide a reasonable basis for our 

findings and conclusions based on our audit objectives. We believe that 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives.

We also interviewed 

officials from Interior and the oil and gas industry to identify the 

capabilities that U.S.-based and international organizations use to 

address subsea well blowouts. To determine the potential to use subsea 

well containment capabilities available for the Gulf of Mexico in other 

federal waters, such as those along the Alaskan coast, we reviewed 

documents and interviewed officials from Interior responsible for 

permitting in Alaskan waters as well as operators and industry groups.

According to a 2010 Interior study, 97 percent of oil and gas production in 

federal waters occurs along the U.S. outer continental shelf of the Gulf of 

Mexico. The outer continental shelf is the submerged lands outside the 

territorial jurisdiction of all 50 states but within U.S. jurisdiction and 

control.5 The outer continental shelf contains an estimated 85 billion 

barrels of oil, and over half of this oil is located in the Gulf of Mexico.6

Interior is responsible for the oversight of oil and gas activities on the U.S. 

outer continental shelf, which includes submerged lands in federal waters 

off the coast of Alaska, in the Gulf of Mexico, and off the Atlantic and 

Significant reserves also exist in the outer continental shelf off Alaska.

 

4

Because this was a nonprobability sample, we cannot generalize the information derived 

from these well containment plans to all such plans; these plans provide examples of 

plans developed by five different operators and different well depths, ranging from 3,300 

to 6,600 feet.

5

The outer continental shelf consists of submerged federal lands, generally extending 

seaward between 3 and 200 nautical miles off the coastline. 

6

This estimate is according to a 2006 Interior assessment of technically recoverable 

resources, not all of which may be economically recoverable. 

Background 
 

Page 4 GAO-12-244 Subsea Well Containment

Pacific coasts.7

Also under its oversight responsibilities, Interior issues guidance called a 

Notice to Lessees and Operators to clarify, supplement, or provide more 

detail about certain requirements, including requirements for applications 

for permit to drill. In response to the Deepwater Horizon incident, Interior 

As part of its responsibilities, Interior leases blocks of land 

in the outer continental shelf for mineral development, including oil and 

gas exploration and production. The lease holder may operate the well or 

may hire other companies to perform drilling operations and other related 

services. Operators submit a series of documents to Interior for approval 

to drill, including an application for permit to drill and an oil spill response 

plan. In October 2010, Interior promulgated certain new requirements for 

the application for permit to drill process designed to prevent a blowout 

including, among other things, requiring independent third-party 

verification that the subsea blowout preventer is compatible with the 

specific well location and well design. The oil spill response plan is to 

include an operator’s proposed methods for ensuring that oil spill 

containment and recovery equipment and response personnel are 

mobilized and deployed in the event of a spill. This plan is to be 

implemented immediately following a spill. The plan is also to include an 

inventory of spill response resources such as materials and supplies, 

services, equipment, and response vessels available locally and 

regionally, as well as a description of the operator’s procedures for 

conducting monthly inspections and necessary maintenance of recovery 

equipment. As part of its oversight responsibilities, Interior is required to 

conduct scheduled and unscheduled inspections of offshore facilities, 

such as drilling rigs and production platforms. Equipment scheduled for 

inspections includes equipment designed to prevent or alleviate blowouts, 

fires, spillages, or other major accidents.

 

7

In April 2010, Interior initiated a reorganization of its bureau responsible for overseeing 

offshore oil and natural gas activities. Specifically, in May 2010, Interior announced that it 

would be reorganizing its Minerals Management Service—the bureau previously tasked 

with overseeing offshore oil and natural gas activities into three separate bureaus: the 

Bureau of Ocean Energy Management (BOEM), the Bureau of Safety and Environmental 

Enforcement (BSEE), and the Office of Natural Resources and Revenue (ONRR). In June 

2010, Interior announced that the former Minerals Management Service would be known 

as the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE). 

Effective October 1, 2010, ONRR became an office under the Interior’s Assistant 

Secretary-Policy, Management and Budget. On October 1, 2011, BOEM—which oversees 

leasing and resource management, and BSEE, which is responsible for issuing oil and 

natural gas drilling permits and conducting inspections—began functioning as separate 

bureaus. 
 

Page 5 GAO-12-244 Subsea Well Containment

issued a number of these notices, which, among other things, notified 

operators that Interior would be evaluating whether they had submitted 

adequate information about their well containment capabilities with their 

oil spill response plans. Specifically, in a November 2010 notice, Interior 

informed operators that it would evaluate whether operators could 

demonstrate that they had access to and could deploy well containment 

resources that would be adequate to promptly respond to a blowout or 

other loss of well control. This notice applies only to operators conducting 

operations using subsea blowout preventers, which are devices placed on 

wells to help maintain control over pressures in the well, or blowout 

preventers on floating facilities. Operators provide information on their 

well containment capabilities to Interior in a collection of documents that 

compose a well containment plan. According to Interior officials, all 

approved applications for permit to drill subject to the November 2010 

notice have included a well containment plan. For additional information 

on the types of information operators provide in their well containment 

plans, see appendix I.

There are three phases to produce oil or gas from a subsea well: drilling, 

completion, and production. During the drilling phase, operators drill a 

hole, called the wellbore, from the seafloor down to the reservoir of oil or 

gas. Early in this phase, a blowout preventer is placed on top of the 

wellhead, which, in turn, is installed on top of the wellbore to provide an 

interface between the wellbore and other equipment. A large-diameter 

pipe called the riser connects the drilling rig to the blowout preventer, and 

the drill pipe, drill bit, drilling mud, and casing are routed down to the well 

through the riser and blowout preventer.8

 

8

Casing is a metal pipe that is inserted inside the wellbore to prevent high-pressure fluids 

outside the formation from entering the well, and to prevent drilling mud inside the well 

from fracturing fragile sections of the wellbore. As drilling progresses with depth, casings 

that are slightly narrower than the hole created by the drill bit are inserted into the wellbore 

and bonded in place with cement, sealing the wellbore from the surrounding formation. 

Drilling mud is special fluid pumped through the wellbore at different densities to maintain 

a pressure balance inside the wellbore, lubricate the drilling bit, and bring rock and other 

matter cut from the formation back to the rig.

Industry officials we spoke with 

said that during the drilling phase, operators must constantly balance the 

pressure of the drilling mud inside the wellbore with the pressure from the 

surrounding formation thousands of feet below the seafloor. Interior 

officials explained that during this phase, operators may encounter a 

number of unknown well conditions, which if not controlled or corrected 

could pose a risk of a blowout. During a blowout, operators close the 
 

Page 6 GAO-12-244 Subsea Well Containment

valves in the blowout preventer in an attempt to seal the wellbore and 

prevent oil and gas from escaping to the surface. Figure 1 illustrates the 

drilling phase.
 

Page 7 GAO-12-244 Subsea Well Containment

Figure 1: Key Equipment Used during the Drilling Phase

Note: Objects in figure are not to scale.
 

Page 8 GAO-12-244 Subsea Well Containment

In the second phase, known as completion, the operator opens the 

wellbore to allow the flow of oil and gas from the reservoir, and installs 

equipment at the top of the wellbore to control and collect the oil and gas. 

The third phase is production, the extraction of oil or gas from the well.9

The difficulty of the drilling process can vary depending on the depth of 

the seafloor as well as the depth of the reservoir. According to a 2010 

Interior study, the majority of oil production in the Gulf of Mexico occurs in 

deep water, which the study defined as 1,000 feet or more below sea

level.10

According to several studies of the Deepwater Horizon incident, drilling 

had already been completed when high-pressure oil and gas 

unexpectedly breached a cement barrier placed inside the wellbore. This 

allowed oil and gas to flow unimpeded up the riser to the Deepwater 

Horizon drilling rig on the surface, resulting in an explosion.

Deepwater wells tend to produce a relatively large amount of oil 

and gas compared with wells in shallower water, in part because high 

reservoir pressures contribute to well productivity. These high pressures 

also make drilling deepwater wells significantly more dangerous than 

drilling shallow wells because, among other things, the increased 

pressure can exacerbate the effects of a blowout and make a well 

containment response more challenging. In the case of the well that the 

Deepwater Horizon was drilling, the seafloor was nearly 5,000 feet below 

sea level, and the operator, BP, drilled an additional 13,000 feet below 

the seafloor to reach the reservoir.

11

 

9

Before the production phase begins, the blowout preventer is removed to allow 

installation of equipment for producing oil or gas. 

As a result, 

the Deepwater Horizon drilling rig caught fire and sank roughly 36 hours 

later. Over the next 87 days, BP made numerous attempts to stop the 

flow of oil from the well but was unsuccessful until it installed a capping 

stack, a device similar to but generally smaller than a blowout preventer 

10According to a 2011 report by the National Commission on the BP Deepwater Horizon

Oil Spill and Offshore Drilling, companies and governmental organizations have adopted 

definitions for deepwater ranging from 600 to 1,500 feet.

11The crew of the Deepwater Horizon drilling rig attempted to stop the flow of oil and gas 

by closing the blowout preventer after the fluids had entered the riser, but this failed to 

seal the well.
 

Page 9 GAO-12-244 Subsea Well Containment

that is specifically designed to cap a well after a blowout.12 While the 

blowout preventer is designed to manage drilling operations and prevent 

a blowout, a capping stack is designed to be deployed after a subsea 

blowout has already occurred. At the time of the Deepwater Horizon 

incident, there were few capping stacks in existence, and capabilities to 

support subsea well containment were limited.

Since the Deepwater Horizon incident, the oil and gas industry has 

improved its capabilities to respond to a subsea well blowout in the Gulf 

of Mexico. In particular, operators have formed two new organizations 

that are expected to offer improved well containment capabilities, 

including more effective equipment and services, and expertise to 

member operators in the event of a well blowout. The subsea well 

containment capabilities available for the Gulf of Mexico consist primarily 

of existing technologies that have been modified to support well 

containment.

Following the Deepwater Horizon incident, two not-for-profit organizations 

of oil and gas companies—the Marine Well Containment Company 

(MWCC) and the Helix Well Containment Group (HWCG)—formed to 

provide subsea well containment capabilities and support to operators in 

the Gulf of Mexico that enter into contracts with them. Once under 

contract and in the event of a spill, each of these well containment 

organizations is to provide certain containment equipment and services—

capping stacks, vessels, and other resources necessary to respond to a 

subsea blowout—that operators can customize to their well containment 

needs. Equipment and services provided by these well containment 

organizations were developed in consultation with Interior and have been 

a key part of the well containment plans that operators submit to Interior, 

according to Interior officials. All of the operators subject to Interior’s 

November 2010 notice that have received permission to drill in the Gulf of 

Mexico since the moratorium was lifted have contracted with one or both 

 

12According to a 2011 report by the National Commission on the BP Deepwater Horizon

Oil Spill and Offshore Drilling, the well was closed permanently when BP drilled a relief 

well that intersected the problem well and then pumped concrete into the problem well to 

seal the wellbore. Interior also published a Drilling Safety Rule in October 2010 that 

included provisions intended to help improve blowout prevention practices in order to 

enhance the safety of oil and gas drilling operations.

Industry Has 

Improved Its 

Capabilities for 

Subsea Well 

Containment in the 

Gulf of Mexico

Two Industry 

Organizations Provide 

Subsea Well Containment 

in the Gulf of Mexico
 

Page 10 GAO-12-244 Subsea Well Containment

of these well containment organizations to provide certain well 

containment equipment and resources in the event of a subsea blowout, 

according to these officials.

In general, MWCC members include some of the largest operators with 

oil and gas exploration and production activities in the Gulf of Mexico, 

such as ExxonMobil, ConocoPhillips, Chevron, and Shell, and HWCG 

members include operators of various sizes. Some operators are 

members of both groups. More specifically:

• MWCC operates as an independent, stand-alone company where 

each of its 10 members has equal ownership and voting rights, and 

according to MWCC representatives, its members drilled 

approximately 70 percent of deepwater wells drilled in the U.S. Gulf of 

Mexico from 2007 through 2009.

• HWCG is a consortium of 24 operators, which, according to HWCG 

representatives, represent approximately 80 percent of the deepwater 

operators in the Gulf of Mexico. HWCG was created around the well 

containment capabilities offered by one deepwater services company 

whose equipment was used in the response to the Deepwater Horizon 

incident.

According to representatives from both well containment organizations, 

members also commit to mutual aid agreements in which operators agree 

to provide equipment or other support to consortium members that 

experience a subsea well blowout. Representatives of the well 

containment organizations said that both HWCG and MWCC also offer 

services to nonmembers on a fee basis. Furthermore, representatives of 

the well containment organizations we spoke with generally agreed that 

should another incident like Deepwater Horizon occur, industry would 

mobilize to make available all of the equipment and services necessary to 

ensure a quick and effective response.

In addition to equipment and services, both MWCC and HWCG provide 

overall plans that identify how the equipment and services are to be 

deployed and used; a schedule of activities to be followed; various 

contingencies for high-risk activities, such as straightening a bent 

wellhead that may have been damaged by a blowout; and names and 

contact information for technical experts who may be called on as 

required. According to Interior officials, operators would need to 

customize the well containment organizations’ overall plans to their 

specific well design. For example, the well pressure would determine the 
 

Page 11 GAO-12-244 Subsea Well Containment

specifications of the capping stack, and the depth of the well would 

specify which ships have cables long enough to reach it. These 

customized plans comprise some of the documents in the well 

containment plans that operators submit to Interior. However, operators 

may need additional equipment and services that the well containment 

organizations do not provide. For example, the well containment 

organizations provide capping stacks for well containment, but in some––

if not all––cases the operator must identify a separate service provider to 

transport the capping stack to the site and deploy it to the well. In their 

well containment plans, operators also identify other needed equipment 

and services that may not be provided by the well containment 

organization, including debris removal equipment, remotely operated 

underwater vehicles, which are controlled from surface vessels and used 

to, among other things, clear debris, and apply chemicals called 

dispersants that are used to disperse leaked oil.

The subsea well containment capabilities that MWCC and HWCG offer 

for the Gulf of Mexico consist primarily of established technologies that 

have been modified to support well containment. For example, according 

to industry representatives, capping stacks are devices similar to 

previously used blowout preventers and contain many of the same 

components. According to representatives from the two well containment 

organizations, the well containment capabilities (i.e., equipment, 

procedures, and processes that MWCC and HWCG would activate in the 

event of a subsea blowout in the Gulf of Mexico) incorporate established 

technologies commonly used for offshore well drilling. Well containment 

capabilities in the Gulf of Mexico include the following:

• containment equipment, including capping stacks used to shut in a 

well, and containment domes and top hats that are used to collect 

escaping oil and gas and flow them to the surface;13

• subsea support systems, such as riser systems that direct captured oil 

and gas to surface vessels in the event that the well cannot be shut in 

completely; utility equipment, such as dispersant injection systems, 

 

13Containment domes and top hats are devices used to collect oil and gas in a subsea 

environment, but their use may be limited under some conditions because hydrocarbons 

can freeze and form hydrates that clog the devices’ collection tubes.

Subsea Well Containment 

Capabilities Available for 

the Gulf of Mexico Consist 

Primarily of Modifications 

to Established 

Technologies
 

Page 12 GAO-12-244 Subsea Well Containment

hydrate inhibitor systems, and hydraulic power systems; manifolds 

and connection systems; and remotely operated vehicles;14

• surface vessels, such as multipurpose containment response vessels 

that can be configured to conduct a variety of drilling or containment 

activities, production vessels that can process captured oil, storage 

tankers to transport the captured oil, and other support vessels used 

to distribute dispersants and control remotely operated underwater 

vehicles.

and

Figure 2 illustrates a subsea well containment response system.

 

14A dispersant is used on the surface and subsea to break up oil and gas into smaller 

particles, making it easier for microorganisms to consume the oil and making it less 

hazardous to responding personnel on the surface. Hydrate inhibitors help in preventing 

subsea oil from freezing up and forming hydrates that can clog tubes that collect and route 

oil and gas to the surface. Hydraulic power systems are situated on the seafloor and 

provide power for remotely operated vehicles and other equipment on the seafloor. 

Manifolds are used to control fluid flow. Remotely operated underwater vehicles are 

controlled from surface vessels and are used to show the debris field, clear debris, and 

activate functions on the blowout preventer and capping stack.
 

Page 13 GAO-12-244 Subsea Well Containment

Figure 2: Subsea Well Containment Response Equipment

Note: Objects in figure are not to scale.
 

Page 14 GAO-12-244 Subsea Well Containment

A key component of both MWCC and HWCG’s response capability is a 

capping stack. According to industry representatives, capping stacks are 

essentially lighter, specialized versions of blowout preventers that use 

similar components to stop or control the flow of oil and gas. The capping 

stacks built for MWCC and HWCG are designed to withstand the high 

pressures experienced in deepwater reservoirs—up to 15,000 pounds per 

square inch for the most recent capping stacks. These stacks can be 

deployed to 10,000 feet below sea level. Most capping stacks have 

multiple outlets that allow oil and gas to be routed to surface vessels and 

processed. Capping stacks are usually deployed on top of the blowout 

preventer but can also be installed on other points, including the 

wellhead. Industry representatives told us that fittings between connection 

points are generally standardized but that capping stacks can be modified 

with different fittings to allow for proper installation. Once a capping stack 

is installed, depending on the scenario, the containment plans typically 

call for slowly closing each of the outlets until the well is closed. In some 

cases, operators may also be able to deploy dispersants into or around 

the capping stack to help break up the oil (see fig. 3).15

 

15GAO is currently conducting work looking at what is known about the use of dispersants, 

efforts by federal agencies and other stakeholders to enhance knowledge on the use of 

dispersants and their effects, and the challenges researchers face in doing so.
 

Page 15 GAO-12-244 Subsea Well Containment

Figure 3: A Capping Stack Ready for Deployment

Capping stacks are a primary component of HWCG and MWCC well 

containment capabilities, but Interior officials told us that it does not 

require operators to use any particular technology in the Gulf of Mexico. 

Instead, Interior expects operators to demonstrate that they have the 

capability to control a well with a capping stack or some other functionally 

equivalent technology, and according to Interior officials, capping stacks 

have demonstrated that capability. Industry representatives told us that 

capping stacks are tested periodically and physically located near staging 

points around the Gulf of Mexico, where they can be moved offshore 

rapidly. When not needed, they are stored onshore and not used for any 

other purpose. Representatives from both HWCG and MWCC told us that 

both of their organizations have multiple capping stacks ready for 

deployment.

In addition to capping stacks, well containment capabilities rely on other 

equipment and services to transport the capping stack to the well site, 

assist with debris removal, and collect oil and gas from the capping 
 

Page 16 GAO-12-244 Subsea Well Containment

stack.16 This equipment includes surface vessels that can collect oil and 

gas from the capping stack or other collection devices, vessels with lift 

and hoist capabilities to position and move the capping stack, control 

ships with electronics to monitor the pressures and status of the capping 

stack, and remotely operated vehicles that perform a variety of subsea 

operations. In their well containment plans, operators provide Interior with 

a list of this other equipment as well as how it could be utilized and 

positioned at the blowout location.

Following the Deepwater Horizon incident, Interior issued new guidance 

that identified information operators are to provide to demonstrate well 

containment capability, but Interior has not fully documented its internal 

process for reviewing this information. Also, the well containment plans 

that operators submit to Interior as part of the permitting process identify 

equipment, such as a capping stack, that would be needed for well 

containment response, but Interior has not yet documented its process for 

ensuring that this equipment is regularly inspected and available. Finally, 

while Interior has conducted two unannounced spill drills that 

incorporated scenarios for well containment, it has not documented a time 

frame for incorporating these tests in the future.

Interior issued guidance following the Deepwater Horizon incident that 

identifies information that operators are to provide to demonstrate they 

can respond adequately and promptly to a blowout or other loss of well 

control, but the agency has not documented its process for reviewing the 

information it receives. A Notice to Lessees and Operators issued on 

November 8, 2010, after Deepwater Horizon, identifies specific 

information, including types of well containment equipment accessible to 

the operator in the event of a spill, that operators are to provide to Interior 

to ensure that operators’ spill response plans are adequate. Interior 

issued subsequent supplemental guidance on the November 2010 notice 

 

16The riser between the drilling rig and the wellhead can collapse after a blowout and may 

create a large debris field on top of the well that the operator must clear before 

proceeding. 

Interior Has Issued 

New Guidance and Is 

Documenting Many of 

Its Oversight 

Processes, but Has 

Not Documented a 

Time Frame for 

Testing Operators’ 

Responses to a 

Subsea Blowout

Interior Issued New 

Guidance and Is 

Documenting a Process for 

Providing Oversight
 

Page 17 GAO-12-244 Subsea Well Containment

on December 13, 2010, explaining that it would review this information as 

part of the application for permit to drill approval process. For example, 

operators are to provide information describing their plans to use capping 

stacks; containment domes; subsea utility equipment, including hydraulic 

power, hydrate control, and dispersant systems; riser systems; remotely 

operated underwater vehicles; and oil collection vessels. Operators may 

satisfy these new information requirements by submitting a well 

containment plan as part of their oil spill response plans.

Interior officials told us that they discuss their expectations for the 

contents of these plans with individual operators but noted that the 

agency has not finalized documentation of these expectations or 

completed the documentation of its internal process for reviewing these 

plans. Interior officials who review these plans have developed a onepage checklist outlining the types of information they review, but the 

checklist does not provide criteria for assessing the information. For 

example, the checklist asks “Does the plan adequately address debris 

removal?” but does not provide criteria for determining whether the 

information the operator included is adequate. These officials said they 

are in the process of documenting their review process and expect to 

have the documentation in place by spring 2012.

Under the Standards for Internal Control in the Federal Government, 

federal agencies are to employ control activities, such as to clearly 

document internal control in management directives, administrative 

policies, or operating manuals, and the documentation is to be readily 

available for examination.17

 

17See GAO, Standards for Internal Control in the Federal Government, 

Interior officials told us that the agency plans 

to transfer the responsibility for reviewing well containment plans to 

another office in 2012, and will document the review process before that 

time. In the meantime, Interior officials told us that they rely on the 

expertise and judgment of staff to perform these reviews and 

communicate their expectations to operators. Until the agency completes 

a documented review process, Interior cannot provide reasonable 

assurance that well containment plans will be reviewed consistently.

GAO/AIMD-00-21.3.1 (Washington, D.C.: November 1999). These standards, issued 

pursuant to the requirements of the Federal Managers’ Financial Integrity Act of 1982, 

provide the overall framework for establishing and maintaining internal control in the 

federal government.
 

Page 18 GAO-12-244 Subsea Well Containment

In addition to the new guidance issued since the Deepwater Horizon

incident, as part of Interior’s review of well containment plans, Interior and

operators use a new software tool to analyze a proposed well’s design 

and its ability to withstand increased pressures that result when an 

uncontrolled well is closed by a capping stack. In certain situations, 

capping the well shut could cause portions of the well to burst, potentially 

allowing oil and gas to flow up through the seabed and releasing oil and 

gas into the sea from outside the wellbore. This new software tool, called 

the well containment screening tool, helps Interior and operators evaluate 

whether a well could be closed using a capping stack and still maintain 

wellbore integrity. The development of this screening tool was initiated by 

Interior and completed with input from the oil industry. The screening tool 

analyzes potential well integrity and risk based on various factors 

including well design, geological characteristics, reservoir pressures, and 

wellbore fluid gradients. Interior provides the tool to operators and then 

reviews each operator’s analysis of expected wellbore integrity; following 

this review, Interior may advise operators to adjust screening tool 

parameters when appropriate. According to Interior officials, on at least 

12 occasions, an operator strengthened its wellbore design based on the 

results of the screening tool. Industry representatives we met with also 

said that the screening tool was valuable for helping address the risks 

associated with a subsea blowout by requiring operators to document 

their well design decisions and have those decisions reviewed by Interior. 

According to Interior officials, in some cases, Interior may have access to 

a wider set of data on the geological characteristics of the area than the 

operator. In these cases, Interior can advise the operator on the need to 

modify its well design.

As previously stated in this report, since the Deepwater Horizon incident, 

the well containment plans that operators submit to Interior as part of the 

permitting process identify equipment that the operator plans to use to 

contain subsea well blowouts. However, Interior does not have a fully 

documented process and associated schedule to ensure that the 

equipment is regularly inspected and available for deployment. Interior 

regulations that have been in place since before the Deepwater Horizon

spill specify that operators are to submit an oil spill response plan that 

identifies procedures the operator is to follow in the event of a spill, 

including methods to ensure the availability of oil spill response 

equipment and an inventory of this equipment and the operator’s 

procedures for conducting monthly inspections. Interior is also required to 

conduct inspections of offshore facilities and response equipment. Interior 

has scheduled inspections of surface response equipment but has not 

Interior Is Documenting Its 

Process to Ensure 

Equipment Is Inspected 

and Available, but Has Not 

Documented a Time Frame 

for Incorporating Well 

Containment Scenarios 

into Unannounced Spill 

Drills
 

Page 19 GAO-12-244 Subsea Well Containment

scheduled regular inspections of well containment equipment. Interior 

officials we met with told us that they have observed officials from the well 

containment organizations conducting certain tests of all capping stacks 

identified in well containment plans approved for the Gulf of Mexico.18

While Interior does not have a documented process for monitoring the 

availability of equipment that operators identify in their well containment 

plans, this concern is somewhat mitigated by the number of vessels and 

capping stacks located in the Gulf of Mexico that could aid a well 

containment response in the event that dedicated equipment is 

unavailable. Interior officials told us that they expect well containment 

plans to list multiple replacement vessels and equipment to demonstrate 

this redundancy, and these officials believe this sufficiently mitigates the 

possibility that resources could be unavailable in the event of a subsea 

blowout. In addition, Interior relies on operators to inform them when well 

containment equipment is unavailable, and industry representatives told 

us that the two well containment organizations are to inform their 

members and Interior when critical equipment is out of service.

These tests include pressure tests to ensure that the capping stack can 

withstand well pressures, and functional tests to ensure that components 

operate properly. However, Interior officials told us that the agency does 

not have a regular schedule for inspecting such equipment and does not 

specify what tests should be conducted to ensure that the equipment is in 

operational condition. The officials added that by June 2012 Interior plans 

to have a process that (1) establishes a schedule for testing equipment 

and (2) identifies the tests that will be conducted as part of the agency’s 

oversight of operator readiness to respond to a subsea event.

In addition, Interior has not determined the extent to which it will conduct 

drills to test operators’ abilities to respond to a subsea well blowout. 

Interior’s regulations provide for periodic unannounced drills to test the 

spill response preparedness of operators, but Interior has not set a time 

frame for incorporating well containment scenarios into these exercises 

that would test operators’ abilities to implement their well containment 

plans. Interior conducts these drills to, among other things, test an 

operator’s ability to notify the appropriate entities and personnel in the 

 

18Although not explicitly required by Interior, capping stacks have been included in all well 

containment plans that have been approved by Interior. Interior officials told us that it does 

not require capping stacks as part of the well containment plan because it does not want 

to limit industry’s use of alternative technologies to contain well blowouts.
 

Page 20 GAO-12-244 Subsea Well Containment

event of a spill, including federal regulatory agencies, affected state and 

local agencies, internal response coordinators, and response contractors, 

and to take appropriate action to implement the operator’s response plan. 

If the decisions made during the drill do not align with the approved oil 

spill response plan, the drill provides an opportunity to determine what 

needs to change in the response process. In September 2011, Interior 

conducted its first unannounced spill drill that included a subsea well 

containment scenario, and held a second unannounced drill in December 

2011. According to Interior officials, the agency plans to incorporate 

subsea well containment scenarios in certain future unannounced spill 

drills with operators. According to these officials, Interior staff have 

observed well containment exercises conducted by the two well 

containment organizations in the Gulf of Mexico. However, Interior has 

not tested most operators’ ability to respond to a subsea blowout, and has 

not established a time frame to incorporate these tests into unannounced 

spill drills. Until Interior sets a time frame for incorporating well 

containment scenarios into unannounced spill drills, there is limited 

assurance that operators are prepared to respond to a subsea blowout.

Subsea well containment capabilities similar to what industry offers for the 

Gulf of Mexico could generally be used in other federal waters, including 

the outer continental shelf off Alaska. Industry officials said that they are 

developing a well containment response capability for use in this region. 

Moreover, operators of subsea wells off the Alaskan coast are likely to 

face operating conditions that pose different environmental and logistical 

risks than those faced in the Gulf of Mexico and may require modified 

blowout response plans.

According to industry representatives and Interior officials we spoke with, 

capping stacks and other equipment available to respond to blowouts in 

the Gulf of Mexico could be used in other federal waters. For example, 

because capping stacks are installed on top of the wellhead or blowout 

preventer, they are not affected by the condition of the seafloor, so they 

could be used in other regions. Industry representatives explained that 

the connection points between subsea devices like wellheads, blowout 

preventers, and capping stacks are mostly standardized and that these 

connections can be exchanged on a capping stack to ensure a proper 

Subsea Well 

Containment 

Capabilities Available 

for the Gulf of Mexico 

Could Be Used in 

Other Federal Waters, 

but Environmental 

and Logistical Risks 

Differ

Capabilities Available for 

the Gulf of Mexico Could 

Be Used in Other Regions
 

Page 21 GAO-12-244 Subsea Well Containment

fit.19 Capping stacks may be specialized for particular regions, but Interior 

officials and industry representatives told us that capping stacks 

developed for use in the Arctic would not need to manage the same 

pressures as capping stacks developed for use in the Gulf of Mexico 

because reservoir pressures in the Gulf of Mexico are generally much 

higher.

For the past two decades, the majority of subsea oil and gas exploration 

and production in U.S. waters has occurred in the Gulf of Mexico; 

however, in 2010, Shell Oil submitted plans to Interior to drill in the waters 

north of Alaska as early as the summer of 2012.20 In August 2011, Interior 

conditionally gave approval to Shell Oil to drill exploratory wells along the 

north shore of Alaska in the Beaufort Sea, pending receipt and approval 

of Shell’s well containment plans and other requirements.21 In December 

2011, Interior conditionally gave approval to Shell to drill in the Chukchi 

Sea, again pending receipt and approval of Shell’s well containment plans 

and other requirements.22

 

19Interior officials told us that they expect operators that use a capping stack as part of a 

well containment response plan to demonstrate to Interior that the capping stack can be 

attached to each of the potential connection points on an uncontrolled well.

If Shell submits these materials to Interior and 

Interior approves them, Shell could begin drilling in these areas early as 

the summer of 2012. Figure 4 illustrates the location of the Beaufort and

Chukchi Seas relative to Alaska and the Arctic Circle.

20In August 2011, ConocoPhillips submitted a draft exploration plan for the Chukchi Sea.

21Interior’s approval is also subject to a petition for review by environmental groups. 

Petition at 2, Native Village of Point Hope, et. al. v. Salazar, et. al., No. 11-72891 (9th Cir. 

filed Sept. 29, 2011). Environmental groups have also challenged a permit issued by the 

Environmental Protection Agency (EPA) to Shell under the Clean Air Act for emissions 

from the Kulluk drilling unit and vessels that Shell proposes to use for exploratory drilling 

in the Beaufort Sea. That challenge is currently pending in front of EPA’s Environmental 

Appeals Board.

22One condition of Interior’s approval for exploratory drilling in both the Beaufort and 

Chukchi Seas is Shell’s receipt of an approved Marine Mammal Protection Act (MMPA) 

authorization and Interior’s receipt of a corresponding Endangered Species Act Incidental 

Take Statement. The National Oceanic and Atmospheric Administration released a draft 

environmental impact statement exploring these points in December 2011. 

Industry Is Developing 

Well Containment 

Capabilities for the Alaska 

Outer Continental Shelf
 

Page 22 GAO-12-244 Subsea Well Containment

Figure 4: The Beaufort and Chukchi Seas off the Coast of Alaska

According to Shell representatives, the company is still developing the 

capabilities that it will need to support well containment operations in the 

Beaufort and Chukchi Seas. These capabilities are to include a capping 

stack similar in design and functionality to capping stacks already 

inspected and approved for use in the Gulf of Mexico.23

 

23Trendsetter Engineering built capping stacks for MWCC and HWCG and is designing 

and fabricating Shell’s capping stack. 

Shell’s capping 

stack has been specifically designed for use in Arctic waters and, 
 

Page 23 GAO-12-244 Subsea Well Containment

according to Shell representatives, is expected to be completed by April 

2012.

According to Shell representatives we spoke with, Shell is to have 

dedicated capping and containment capabilities at sea and ready for 

deployment. In the event of a subsea well blowout, Shell will deploy a 

capping stack as its primary response. The capping stack is to be housed 

on an icebreaking vessel supporting drilling operations in the Beaufort 

Sea, according to the Shell representatives.24 The icebreaking vessel is to 

have the lifting capability to deploy the stack onto an uncontrolled well. 

Shell representatives said that if a blowout occurred on a well in the 

Chukchi Sea, operations in the Beaufort Sea would be shut down and the 

icebreaking vessel with the capping stack and other supporting vessels 

would be deployed from the Beaufort Sea to the Chukchi Sea.25 Likewise, 

in the event of a well blowout in the Beaufort Sea, Shell would cease 

operations in the Chukchi Sea and send support vessels to assist 

operations in the Beaufort Sea.26

Subsea drilling operations in Alaska will face operating conditions that 

greatly differ from those in the Gulf of Mexico and may pose unique risks. 

For example, the Beaufort and Chukchi Seas are inside the Arctic Circle, 

with cold and icy conditions for much of the year and with few daylight 

hours during the winter. Interior and Coast Guard officials said that a well 

containment response in Alaskan waters might face certain risks that 

could delay or impede a response to a blowout.27

 

24According to Shell officials, Shell has contracted with a Finnish company to provide the 

icebreaking vessels Nordica and Fennica to support operations in the Beaufort and 

Chukchi Seas. 

For example, if a 

25In the event of a subsea well blowout, the drilling rig could become disabled. According 

to Shell documents, in such an event the drilling rig at the other site would be required to 

drill relief wells at the blowout site. 

26Chukchi Sea operations would also include an icebreaking vessel but without the 

capping stack.

27Shell representatives told us that the prospects in some areas of the Beaufort and 

Chukchi Seas pose less risk than prospects for some wells in the Gulf of Mexico because 

the wells in Alaska will be situated 100 to 150 feet below the surface, would generally 

have much lower reservoir pressures, and the rate at which oil and gas would flow from a 

well blowout would be much lower than the rate for wells drilled in deeper waters in the 

Gulf of Mexico.

Alaska’s Operating 

Conditions Pose Risks to 

Subsea Well Containment
 

Page 24 GAO-12-244 Subsea Well Containment

blowout were to occur at the end of the drilling season in late October, 

surface ice and temperatures could pose risks to a well containment 

response.

28

Even with Shell’s plans to have dedicated capping stack and well 

containment capabilities in the region to provide rapid response in the 

event of a blowout, these dedicated capabilities do not completely 

mitigate some of the environmental and logistical risks associated with 

the remoteness and environment of the region. Environmental challenges 

include the following:

• Surface ice. According to Interior officials, Shell proposes to drill from 

July 15 through October 31, except for a period in late August to allow 

for whale hunting by the indigenous population. A regional drilling 

expert told us that if a blowout occurred late in the season, icy 

conditions in November and December could make well containment 

challenging. Shell plans to maintain an icebreaking vessel at each 

drilling site to conduct ice management operations, but these 

conditions could still pose a challenge to well containment response.

• Ice scouring. In addition to ice that can accumulate on the surface of 

the ocean, in shallow waters, floating ice can scrape along the surface 

of the seafloor. This has the potential to damage the wellhead and 

blowout preventer, as well as other well containment equipment on 

the seafloor. Shell representatives told us that Shell will place the 

wellhead and blowout preventer in a hole on the seafloor to prevent 

damage from ice scouring. However, this does not eliminate the 

possibility that the capping stack or other equipment placed on or 

above the seafloor, such as dispersant systems or risers, could be 

obstructed or damaged by floating ice.

Logistical challenges include the following:

• Limited infrastructure. Shell officials told us that they will have selfsufficient, dedicated subsea well containment capabilities situated on 

vessels in the Arctic seas during drilling operations. Nonetheless, 

these officials told us that additional personnel would be needed to 

 

28As part of Interior’s conditional approval of Shell’s exploratory drilling plans for the 

Chukchi Sea, Interior will not allow drilling beyond September 24, 2012, for any drilling 

activities that could penetrate an area with oil and gas. 
 

Page 25 GAO-12-244 Subsea Well Containment

respond to a subsea well blowout. Moving personnel to the site could 

delay a response, since harbors, airstrips, and hotels necessary to 

support personnel are limited in number and size along Alaska’s 

northern shore. The facilities are also generally much farther from the 

drilling sites than they are in the Gulf of Mexico, and harbors and 

airstrips have much less capacity to move and support response 

personnel.

• Lack of redundant vessels and equipment. According to Interior 

officials, because of the low rate of offshore production in the outer 

continental shelf off Alaska compared with the Gulf of Mexico, there is 

not an established industry in Alaska to manage subsea oil production 

or respond to a subsea blowout. Therefore, the availability of vessels 

and equipment to provide additional support to respond to a subsea 

well blowout may be limited. For example, we reported in October 

2010 that U.S. Coast Guard infrastructure and assets for Arctic 

missions are limited, including by fuel capacity, distance to fuel 

sources, and crew rest requirements.29

Because Interior has not seen or evaluated Shell’s well containment plans 

and other required documents, it is too early for us to evaluate Interior’s 

oversight of oil and gas development and well containment capabilities in 

Alaskan waters. However, the existence of different types of risk and the 

limited response infrastructure pose additional challenges Interior will 

have to address to conclude that it is providing sufficient oversight.

Shell representatives told us 

that the company plans to have two concurrent drilling operations 

capable of providing mutual assistance, but there are few additional 

resources available in the region to respond in the event that Shell’s 

capabilities are insufficient.

Since the Deepwater Horizon incident, Interior has strengthened its 

oversight of the oil and gas industry’s ability to respond to a subsea well 

blowout, and industry has responded by improving well containment 

capabilities and creating dedicated well containment organizations. 

Interior is developing and documenting oversight processes, and in some 

cases has established time frames for completion. For example, while 

 

29GAO, Coast Guard Efforts to Identify Arctic Requirements Are Ongoing, but More 

Communication about Agency Planning Efforts Would Be Beneficial, GAO-10-870

(Washington, D.C.: Sept.15, 2010).

Conclusions 
 

Page 26 GAO-12-244 Subsea Well Containment

Interior has not fully documented its well containment plan review 

process, Interior officials told us that they expect to have documentation 

in place by spring 2012. Interior has also not established a regular 

inspection process for well containment equipment listed in well 

containment plans, but Interior officials told us that they are developing 

such a process for this equipment and plan to have it in place by June 

2012. Similarly, Interior does not have a documented process for 

monitoring the availability of equipment identified in operators’ well 

containment plans, but Interior requires operators to list multiple and 

redundant vessels and equipment in their well containment plans, and 

Interior officials believe this sufficiently mitigates the risk if certain 

equipment is unavailable. The availability of redundant vessels and 

equipment found in the Gulf of Mexico does not exist in Alaska, however, 

and is something that Interior will need to consider as it receives and 

evaluates Shell’s plans to drill in waters off Alaska. Finally, Interior has 

conducted two unannounced spill drills that have included a subsea well 

containment scenario, and Interior officials told us it will incorporate these 

scenarios into future spill drills. However, Interior has not established a 

time frame for incorporating subsea well containment scenarios into spill 

drills and until it does so, there is limited assurance that operators drilling 

in the Gulf of Mexico or other areas will be prepared to respond to a 

subsea well blowout.

To help ensure that operators are prepared to respond to a subsea 

blowout, we recommend that the Secretary of the Interior document a 

time frame for incorporating well containment response scenarios into 

unannounced spill drills.

We provided a draft of this report to the Department of the Interior for 

review and comment. We received written comments from Interior’s 

Acting Assistant Secretary for Land and Minerals Management, which are 

reproduced in appendix II. The Acting Assistant Secretary concurred with 

our recommendation, stating that Interior agrees that well containment 

response scenarios that test operator responses to subsea blowouts 

should be a regular element in its annual plan for unannounced spill drills. 

The Acting Assistant Secretary also provided technical comments, which 

we have incorporated as appropriate.

Recommendation for 

Executive Action

Agency Comments 

and Our Evaluation
 

Page 27 GAO-12-244 Subsea Well Containment

As agreed with your offices, unless you publicly announce the contents of 

this report earlier, we plan no further distribution until 30 days from the 

report date. At that time, we will send copies of this report to the 

Secretary of the Interior, the appropriate congressional committees, and 

other interested parties. In addition, the report will be available at no 

charge on the GAO website at http://www.gao.gov. 

If you or your staff have any questions about this report, please contact 

Madhav Panwar at (202) 512-6228 or panwarm@gao.gov or Frank Rusco 

at (202) 512-3841 or ruscof@gao.gov. Contact points for our Offices of 

Congressional Relations and Public Affairs may be found on the last page 

of this report. GAO staff that made major contributions to this report are 

listed in appendix III.

Madhav Panwar

Senior Level Technologist, Applied Research and Methodology

Frank Rusco

Director, Natural Resources and Environment
Appendix I: Supplemental Information on 

Typical Components of Well Containment 

Plans

Page 28 GAO-12-244 Subsea Well Containment

We reviewed seven well containment plans submitted by operators. Four 

of the plans relied on Helix Well Containment Group (HWCG) equipment 

and three on Marine Well Containment Company (MWCC) equipment. 

The equipment listed below comprises some of the key components that 

could be used to respond to a well blowout and were included in the well 

containment plans that we reviewed.

A capping stack is a device that helps cap a well—called well shut-in—to 

bring a well under control after a blowout.1 It is designed to sit on top of 

other equipment that sits on top of a subsea well, such as the wellhead or 

a blowout preventer, and forms a high-pressure seal around the well. 

Capping stacks have a combination of gate or ram valves to block fluid 

flow.2 Capping stacks also have side outlet valves that can allow for the 

partial flow of oil, reducing the pressure in the wellbore, if needed. For 

instance, if the well containment screening tool indicates wellbore integrity 

will not allow for a full well shut-in, the side outlet valves will be used to 

direct flow to the surface capture vessels as necessary.3 In this scenario, 

a procedure known as “flow and capture” could be used to partially flow 

the oil to a surface vessel for processing and transport.4

The technical features of all capping stacks designed and developed for 

the Gulf of Mexico are similar and made from pre-engineered 

components commonly used in the oil industry. Capping stacks typically 

feature multiple rams for redundancy. Some stacks are rated for well 

pressures up to 15,000 pounds per square inch (psig) and can operate in 

water depths of up to 10,000 feet. Capping stacks vary somewhat in 

height but are generally about 30 feet tall and weigh approximately 100 

tons.

 

1

“Well shut-in” refers to closing a valve to stop or isolate the flow of fluid from the wellbore. 

2

Gate and ram valves are mechanisms that shut off flow within a pipe. A gate valve 

incorporates a sliding gate or wedge to open or block fluid flow. A ram valve is similar in 

operation to a gate valve, but uses a pair of opposing steel plungers or rams that extend 

toward the center of the wellbore to restrict flow or can be retracted to permit flow. 

3

Well integrity is compromised if oil broaches from below the seafloor to open water. 

4

“Flow and capture” refers to the case where an operator cannot demonstrate that full 

wellbore integrity will be maintained by shutting in the well using a capping stack. In this 

case containment can be approved by Interior only if the operator can adequately 

demonstrate capping, flow back, and collection capability. 

Appendix I: Supplemental Information on 

Typical Components of Well Containment 

Plans

Capping Stacks
Appendix I: Supplemental Information on 

Typical Components of Well Containment 

Plans

Page 29 GAO-12-244 Subsea Well Containment

In response to Deepwater Horizon, the global oil industry formed 

initiatives and advisory groups to design and develop capping stacks. 

Capping stacks that are ready for deployment include the following:

Table 1: Capping Stacks Developed by the Oil Industry

Capping stack owner and 

region of operation Shutting device type

Pressure 

rating(psig)

Water depth 

rating (feet)

Cap and flow 

capability (yes/no)

Marine Well Containment 

Company

(for use in the Gulf of Mexico)

Single ram capping stack 15,000 10,000 Yes

Helix Well Containment Group (for 

use in the Gulf of Mexico)

Dual ram capping stack 10,000 10,000 Yes

Dual ram capping stack 15,000 10,000 Yes

Wild Well Control

(for global use)

Both dual rams and a single ram 15,000 10,000 Yes

Oil Spill Response Ltd.

(for use in the United Kingdom 

Continental Shelf)

Ball valve

a

15,000 10,000 No

Source: GAO analysis of information provided by capping stack owners or operators. 

a

Oil Spill Response Ltd. is a collaboration of seven major oil industry-funded spill response 

organizations and the United Kingdom whose mission it is to harness cooperation and maximize the 

effectiveness of oil spill response services worldwide.

Other containment devices, including top hats, caissons, and cofferdams, 

are used to collect or contain the flow of oil from the wellhead when a 

capping stack cannot be connected, such as when a secure seal cannot 

be achieved. A top hat provides a low-pressure seal and allows for a 

limited collection of oil. A top hat is typically a temporary measure used 

while the operator is evaluating or preparing alternative options. A 

caisson creates a soft seal with the seabed—similar to a top hat––by 

covering the damaged blowout preventer. A cofferdam provides no seal 

to the seabed or the damaged blowout preventer.

A hydraulic control system is used to operate subsurface equipment, such 

as to close rams on a capping stack.

Debris removal equipment, such as shears for cutting pipes and remotely 

operated vehicles, is used to remove debris from around a well, such as 

pipes that have fallen to the seafloor following a blowout. In the event of a 

blowout, debris may need to be removed to access the blowout preventer 

and riser system to install the capping stack.

Other Containment 

Devices

Hydraulic Control System

Subsea Debris Removal 

Equipment 
Appendix I: Supplemental Information on 

Typical Components of Well Containment 

Plans

Page 30 GAO-12-244 Subsea Well Containment

This equipment consists of a seafloor distribution system for injecting 

hydrate inhibitor chemicals and dispersants directly into the flowing oil to 

suppress hydrate formation and disperse the oil.5 Multiple vessels are 

needed to transport and deploy these chemicals.

Risers used for well containment consist of tubing that enables access to 

an offshore well for emergency intervention. These riser systems allow 

the oil flowing through the side outlet lines of a capping stack to be routed 

to the surface for collection and further processing. Risers are used when 

operators determine that it is not safe to completely shut in the well 

because of the potential to compromise well integrity. In this instance, 

risers are attached to a capping stack, after which the well may be killed 

from the top––known as a top kill––by funneling mud through the risers 

and down into the wellbore.6

These vessels include oil capture vessels; support vessels, such as those 

needed to deploy the capping stack; remotely operated underwater 

vehicles; and oil storage facilities. According to MWCC and HWCG, 

during a flow and capture procedure, these vessels are capable of 

handling up to 60,000 barrels of liquid and up to 120 million standard 

cubic feet of gas per day.

These procedures seek to successfully kill the well without compromising 

the well’s integrity.7

 

5

Hydrates are crystalline, ice-like compounds composed of water and natural gas. 

Hydrates can hinder deepwater oil production and transportation by plugging flow lines. 

The conditions that tend to promote hydrate formation include low temperatures and high 

pressures. 

If the well’s analysis determines that its integrity 

would be intact under top kill conditions, then the top kill option is 

generally used. However, if the operator determines that a top kill may 

cause surface broaching, flow and capture is used while the operator 

6

The term “kill” in the oil industry means to stop a well from flowing or having the ability to 

flow into the wellbore. Kill procedures typically involve circulating reservoir fluids out of the 

wellbore or pumping higher-density mud into the wellbore, or both. 

7

Interior officials explained that drilling a relief well is the most reliable means to kill or plug 

a well because the relief well is designed to intercept the blown-out well near the bottom of 

the wellbore, where the source of the blowout exists

Subsea Utility Equipment

Well Containment Riser 

Systems

Support Vessels

Well Kill and Abandonment 

Procedures
Appendix I: Supplemental Information on 

Typical Components of Well Containment 

Plans

Page 31 GAO-12-244 Subsea Well Containment

evaluates options for drilling a relief well to permanently kill the well.8

 

8

A relief well is a well drilled near and deflected into a well that is out of control, making it 

possible to bring that well under control.

The 

well is then plugged with cement and, once the wellbore pressure 

indicates that the well has been killed, the capping stack and blowout 

preventer are removed to the surface.
Appendix II: Comments from the Department 

of the Interior

Page 32 GAO-12-244 Subsea Well Containment

Appendix II: Comments from the Department 

of the Interior 
Appendix II: Comments from the Department 

of the Interior

Page 33 GAO-12-244 Subsea Well Containment
Appendix III: GAO Contacts and Staff 

Acknowledgments

Page 34 GAO-12-244 Subsea Well Containment

Madhav Panwar, (202) 512-6228 or panwarm@gao.gov

Frank Rusco, (202) 512-3841 or ruscof@gao.gov

In addition to the contacts named above, Bill Carrigg, Assistant Director; 

Christine Kehr, Assistant Director; David Bennett; Antoinette Capaccio; 

Nirmal Chaudhary; David Messman; Alison O’Neill; and Kiki 

Theodoropoulos made key contributions to this report.

Appendix III: GAO Contacts and Staff 

Acknowledgments 

GAO Contacts

Staff 

Acknowledgments 

(361285)
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