The Minerals Management Service Pipeline Oil Spill Volume Estimation Model (POSVEM) is a computer-based methodology to estimate discharges from seafloor pipelines. The system is composed of a Release Module and a Near Field Module, linked together with necessary databases through a Graphical User Interface (GUI). The GUI allows the user to sketch a platform – pipeline layout, enter characteristic parameters, and run a quasi-3-phase flow model to estimate the volume of potential or actual leaks. Inputs to the model are parameters describing the configuration and characteristics of a pipeline system, the fluid it contains, and the leak or break from which the discharge occurs. Key outputs are the evolution of the release rate over time, the total mass of oil released, and the mean thickness of any eventual surface slick being formed. Test applications of the software are described.

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Post Macondo, industry publications have discussed the equipment, connections, and interfaces needed for capping and containing a blowing subsea well, but they give little insight into developing a well-specific subsea-capping contingency plan. The planning process described here, which has been used successfully on multiple projects and source-control drills, involves assessing the feasibility of deploying a capping stack from a floating vessel, the weight and stability of the capping stack to overcome the force of the blowout jet, and dynamic flow simulations of closing the capping stack outlets without loss of well integrity. This process not only assesses the feasibility, complexity, and risk exposure of the capping operation, but may also justify further planning, studies, or expenditure.

A blowout contingency plan was made for a gas field in a remote area with water depth exceeding 1600 m. The worst-case discharge analysis for a representative well in the field concluded that the reservoir is capable of producing at a highly prolific rate, which posed a challenge when developing a source control contingency plan that complies with governing regulators’ and operators’ internal requirements. Simulations using a transient multiphase flow simulator showed that the kill requirements could exceed the capability of a single conventional relief well; however, planning to intersect and coordinate a dynamic kill using multiple relief wells involved unacceptable operations risks. Furthermore, considering rig availability, limited pumping resources, and long mobilization times for this region, planning to use multiple relief wells is not a feasable option. A recently developed subsea flow spool system can eliminate the need for multiple relief wells in the case of potentially hard-to-kill blowouts, especially where a dynamic kill using multiple relief wells would involve unacceptable operations risks. Dynamic kill simulation shows that the subsea flow spool, coupled with a supporting mobile offshore drilling unit (MODU), flexible flow lines, a supplementary flow spool, and a casing string placed inside the riser will be able to achieve a successful kill if needed. Furthermore, detailed engineering analysis of triaxial loads, fatigue, and erosion were done for critical hardware components to ensure all potential failure points were addressed. In conclusion, the subsea flow spool is a key component of demonstrating a single-relief well contingency for potentially hard-to-kill blowouts

In the event of a blowout, the kill method that usually has the highest probability of success is a relief-well intervention. After the relief well gains hydraulic communication with the blowing well, a dynamic kill is often used to bring the well under control. In some cases, the pumping operation may call for more than one fluid density, which is referred to as a staged kill. Although the staged-kill technique has been around for a long time and has been successfully used on many blowouts, little information is available on applications, benefits, technical challenges, and operational requirements. In this paper, two case studies demonstrate how a staged kill can successfully kill challenging blowouts under various conditions. One example, for a staged-kill application, is an actual gas-condensate blowout that could not be brought under control with a standard dynamic-kill operation. Staging a heavy kill mud ahead of a lighter mud that would not fracture the exposed formations successfully killed the well. The second example summarizes the results from a relief-well contingency study for a planned high-pressure, ultradeepwater well with a weak formation that would be fractured by the required kill mud. Dynamic simulations demonstrate that a lighter mud circulated ahead of the static kill fluid could bring the well under control without fracturing the weak zones.