Rapid Response to Subsea Source Control Events
Andy Cuthbert
Boots & Coots-A Hallibur ton Service

A new, modular,air-mobile capping stacksystem is introduced that can be quickly mobilized and deployed compared to the existing conventional capping technology currently available in the industry. The new system helps expedite equipment transportation to incident sites, which introduces lower costs and, more importantly, faster response times, which can be crucial for success.

The Joint Industry Task Force (JITF) was created toprovide containment technology and response capabilities for the unique challenges associated with capping a subsea well blowout.The JITF endeavor focuses on enabling the industry to react more quickly to such incidents.However,conventional capping technology can be cumbersome, heavy, and unwieldy, weighing 100 tons or more, which can preclude rapid deployment worldwide, based on limited heavy-lift aircraft availabilityand associated heavy-lifting equipment at airports. To airfreight conventional capping stacks,up to seven Boeing 747 or three Antonov 124 aircraft are required to accommodate the entire system. Each air lift that is required increasesthe complexity, costs, and logistical intricacies to schedule and coordinate the equipment;significant effort is necessary to schedule the landing and take-off of a fleet of aircraft and manage the equipment offloading in the correct reassembly sequence onto flatbed trucks at the destination airport. The new rapid capping stack technology uses a gate-valve system, which decreases the overall weight of the system to 45 tons and significantly reduces the associated logistics and coordination times. This design (Figure 1) allows it to be disassembled into modules that can be transported in two Boeing 747-400 freighters to any location in the world within 48 hours, from take-off to landing, and with a simpler reassembly and testing protocol that significantly improves deployment time.

Similarly suitable vessels of opportunity are necessaryto move the capping stack to the actual incident site.Most seaports generally have sufficient crane capacity to handle a 45-ton gate-valve stack, but certain ports can have limited handling capability or insufficient structural quayside integrity to accommodate the large cranes necessary to manage unwieldy ram-based capping systems .Furthermore, the availability of vessels having a sufficiently high crane capacity for deploying the heavy capping stacks at sea is relatively limited, often resulting in longer delays.Even ifsuch vessels wereavailable in the area, attempting to charter and secure their use at short notice invariablyincreases response times. Comparatively, vessels with the crane capacity to lift a 45-ton gate-valve stack are more readily available.

Existing conventional capping stack systems involve more complex reassembly and component retesting, which directly increases the time necessary to deploy the system, often by several weeks.Subsequently,conventional industry equipment is not specifically designed to be moved rapidly.

Despite these apparent issues, some companies still struggle to come to terms with the fundamental shift in deployment practices needed to createa more complete and accurate response program, and in doing so, fail to provide the necessary assurance that a robust plan for major source control events is being created and managed.

Conventional ram-based designsareinherently limitedby the use of elastomer seals , which are prone to high erosion rates because they are designed to close against pressure instead of flow. Conversely, gate-valve technology does not have the same erosional constraints because it is designed to close against flow from a blowing well. [The gate-valve system has been independently tested and verified to withstand flow at 330,000 barrels of oil equivalent per day (BOE/D) containing 14lb sand content/1,000bbl with a loss of 2mm of material after 6 months.]

Unfortunately, when regulatory frameworks do not provide necessary oversight, companies can struggle to integrate safety case requirements into their long -term planning. While acknowledging that capping response times using conventionally available technology can be prohibitively slow in certain areas, such as eastern Canada, the Gulf of Mexico, east Africa, and the Great Australian Bight, this new technology allows the industry torevamp response times and pre-empt regulatory demands.

Figure 1: Modular air-freightable capping stack .

The rapid capping technology is supported by an industry-unique capping stack deployment evaluation, using powerful analytics for specific sites by means of worldwide historical and predictive environment model access. A unique full -hydrodynamic engineering landing analysis, including turbulent, multiphase computational fluid dynamics (CFD) and nonlinear finite element analysis (FEA), is available to allow dynamic engineering blowout models and fluid/structure interaction and environments. Using sophisticated software and powerful computing capabilities, modeling can include factors, such as dynamically positioned (DP) surface vessel dimensions; sea state, as defined by local metocean conditions; water depth; temperature and salinity; type of suspension system spring force;sixdegrees of freedom provided by the capping stack dynamics ; and remotely operated vehicle (ROV) dimensions and positional control ,accounting for the turbulent jet interaction forces on both the ROV and capping stack. The result is an industry-first, full-fluid interface available for real -time capping coordination among DP vessels, cranes, cables, the capping stack, and ROV.

It is abundantly obvious that the longer an uncontrolled subsea blowout is left uncontained, the worse the situation becomes. Waiting weeks for a capping stack to arrive on location whilehydrocarbons are released unabated into the surrounding marine environmentis unwarranted when a more rapid solution is available. Representing a clear path forward, this new technology provides a package consisting of a truly air-mobile capping stack that can be easily mobilized and deployed within days, including debris clearance and subsea dispersant deployment. It can be combined withblowout preventer (BOP) intervention and containment equipment and is supported by industry-standard well kill capability and plume force analysis. Time is of the essence when attempting to mitigate damage resulting from an unabated subsea blowout.The faster response time provided by this system increases the likelihood of success.