How Does Subsea Well Containment and Incident Response Work?

While deepwater operators take numerous precautions to maintain the safety and control of their well sites, they must also be prepared to contain an incident or subsea “blowout” if one should occur.

Although the number of historic deepwater well containment incidents and accompanying data is very limited, the two main reasons why a subsea blowout might occur would be an equipment failure or failure to balance subsurface reservoir pressure.

A comprehensive, rapid response to a subsea blowout mitigates damage to the environment, protects the health and safety of the community, and minimizes economic impact.

Activate the Response Plan

In the Gulf of Mexico, all subsea operators are required to submit an Oil Spill Response Plan and Regional Containment Demonstration Plan to the Bureau of Safety and Environmental Enforcement (BSEE) before they can begin drilling a well. These plans, updated every two years, serve as a pre-planned strategy for containment and a protocol for managing an emergency response.

If a deepwater well containment incident does occur, the Responsible Party begins by activating their incident response plan – surface and subsurface.  The subsurface component is managed through a Source Control incident command structure, usually activated via a phone call to a dedicated emergency response line.

The emergency response line operator will collect information on the location of the incident, water depth, weather, and any other information that is immediately available.  The emergency response line then feeds out a pre-planned alert to the key stakeholders identified in the Responsible Party’s plan of record.

Many deepwater operators choose to work with a not-for-profit consortium, such as the Gulf of Mexico’s HWCG LLC, to share knowledge between operators about well containment procedures and receive assistance and expertise when responding to a deepwater incident.

Conduct Initial Site Assessment and Gather Information

The operator’s first action, even before attempting to address containment, will be to assess the health and safety of all personnel onboard the rig or floating production platform. Once the wellbeing of personnel has been secured, the Responsible Party will begin an in-depth assessment of the incident site.


A Remotely Operated Vehicle (ROV) will be deployed as soon as possible to collect information about the condition of the wellhead, Blowout Preventer (BOP), Lower Marine Riser Package (LMRP) and the amount of debris.

ROVs can also check for potential environmental factors such as seafloor broaching and the nature of flow from the wellbore. The oil flow is monitored for Volatile Organic Compounds (VOC), which may rise to the surface and adversely affect air quality and the safety of the response team.


Almost immediately after the initial emergency call, the mobilization process for containment equipment and response vessels begins. The information gained from the ROV site assessment helps to further determine which equipment will be most suitable for the conditions at the specific well site.

Launch Incident Command Center and System

Meanwhile, the Responsible Party will have begun to activate their Incident Command Center. The command center serves as the hub for coordination and problem solving efforts, gathering experts in one location to facilitate increased communication.

Additionally, the Responsible Party will begin operating within the National Incident Management System’s Incident Command System (NIMS ICS) to provide structure and governance to the response efforts. The ICS includes a leadership structure of pre-designated experts to head taskforces in engineering and operations.

Gain Access to the Incident Site

Before the operator can attempt to successfully contain the well, it must acquire adequate access to the incident site, which may be impeded by any number of obstacles including a fire, causing the rig to sink or become unusable as a response vessel. To remove the crippled rig blocking access to the well, a mooring company needs to lasso the rig and tow it away from the location.

Once the rig has been removed, additional response vessels can move into position and begin the debris clearing process. Multiple ROVs will be deployed with an arsenal of removal tools including wire saws, hydraulic shears, and chop saws.


The goal of debris removal is to gain access to a mandrel either on the BOP stack or wellhead that allows the operator to latch on and cap the flow.

Deploy Well Containment Equipment and Vessels

The key piece of equipment required for well containment is the capping stack, which latches to the wellhead. A capping stack uses stored hydraulic pressure to close a BOP ram, forming a mechanical seal to reduce pressure and stop the flow of hydrocarbons.

A Subsea Accumulator Module (SAM) provides hydraulic pressure to power the capping stack. An Underwater Distribution Base (UDB) may be utilized to recharge the SAM unit as reserve pressure is depleted.

Subject to Environmental Protection Agency (EPA) approval, certain subsea dispersants may be applied to diffuse a subsea oil plume. This minimizes impact to the environment by maximizing biodegradation through natural processes, preventing the spread of hydrocarbons to environmentally sensitive surface or shore locations and reducing VOCs at the incident surface location to protect responders.

Most capping stacks are rated for conditions at either 10,000 pounds per square inch (psi) or 15,000 psi. Either may be used depending on the water depth and pressure factors at play.

The Well Containment Screening Tool (WCST), filed on record alongside the operator’s application to drill, provides advanced data on geological characteristics, mud line pressure, and retention capacity of a particular well site, determining which stack is appropriate. The Well Containment Screening Tool also indicates whether the well can feasibly be capped or if it needs to flow based on the pressure load on the well bore.

In certain situations, identified in advance of an incident, shutting in the well could cause a build-up in pressure that may potentially lead to a fracture or broach in the sea floor. In these cases, a capture and flow structure for containment is used, safely collecting and transporting hydrocarbons to a storage vessel on the surface.


A large offshore vessel transports the capping stack and other equipment to the incident location where a Mobile Offshore Drilling Unit (MODU) can then deploy it. A MODU is not easily affected by rough weather or sea conditions, making it the most reliable way to place the capping stack on a wellhead. If a MODU were unavailable, however, the operator may deploy a capping stack from a more conventional vessel of opportunity using reeled cable through a process called a Heave Compensated Landing System.

In capture and flow containment systems, a floating production unit vessel connects with flow back equipment to process and store hydrocarbons, mitigating potential discharge to the environment.

Contain and Kill the Incident Well

Once a capping stack has been successfully latched, the operator submits a well kill procedure to BSEE for approval. The Responsible Party kills the well by opening the BOP rams for direct access to the wellbore and implementing one of several available processes, such as a top kill or circulate and kill. These methods involve pumping mud into the wellbore to overbalance reservoir pressures.

As an alternative and backup kill method, a MODU may drill a relief well to intersect the incident well and kill it through those means.

Industry Collaboration

To learn how sixteen deepwater operators have come together leveraging their mutual aid commitments to each other to form a comprehensive, ready and rapid response system in the U.S. Gulf of Mexico, visit HWCG’s website at


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