Summary:
A generally applicable, well containment and intervention capability is a necessary component of an effective system for quickly responding to future deepwater blowouts. Reducing the time required to cap a subsea blowout has the greatest potential for reducing the environmental impact and economic costs associated with such an event. Other collection and clean up responses do not address the fundamental issue of stopping the pollution. The importance of a sealing well containment capability was demonstrated by the capping stack used on the Macondo blowout. It was the first containment response that was effective in stopping additional pollution, and it allowed the “static kill” with mud and then cement. Nevertheless, the capping stack used on the Macondo well was assembled using “off-the shelf” components and had several limitations. It required months to be ready for use. Blind rams were the only closure mechanism, which limited its usefulness for intervention into the well. It had to be bolted to a flange on top of the Macondo lower marine riser package, which limited its strength, pressure rating, and speed of attachment. It relied on the choke and kill line connections of the Macondo preventer for routing flow in and out of the well, which limited the flow rates that it could transport to the surface.
In contrast, a generally applicable, quick response subsea capping system would ideally provide: 1) a high pressure high strength connection to the wellhead, blowout preventer, or lower marine riser package on a well experiencing a subsea blowout, 2) the ability to stop the flow and inhibit hydrate formation, 3) the ability to collect and transport or divert a high flow rate from the well, 4) for bullheading fluids into the well, and 5) for intervention into the well under pressure with either wireline or pipe. It is expected that the “ideal” capping stack will need to be a modular system to have these capabilities and to adapt to the large variability of connector profiles on wellheads and blowout preventers, wide range of plausible flow rates from varied formation pressures in wells and significant variations in operational requirements for diverse situations.
A billion dollar industry consortium is currently developing standby equipment to respond to future subsea blowouts. However, this consortium is strongly influenced by the need to assemble a deployable system quickly so that deepwater drilling projects can be resumed. A qualified, independent group with a history of working on deepwater well control issues provides the advantage of a separate long-term view to define the design issues related to a subsea capping stack system. This design process could result in long term improvements in the systems being deployed and help develop independent expertise for evaluating or providing advice on the application of subsea containment systems.
The proposed research is intended to answer the following questions: 1) what are the minimum, mandatory capabilities for a generally applicable, quick response, subsea capping stack, 2) what supplementary capabilities should be provided by additional modules to achieve all of the functions likely to be necessary for an effective subsea capping, containment, and intervention system, and 3) what are the required sizes, pressure ratings and geometries for these components? Deliverables from the proposed research will include a general description of the proposed modules and computer software for modeling use of system for an appropriate range of water depths, well geometries, and reservoir characteristics.