As the expense of deepwater drilling increases, efforts to eliminate or reduce non-productive time (NPT) can have a significant effect on overall costs. Current standard practices for installing surface casing strings involve multiple trips to first drill the hole section, and then run casing, land the wellhead, and cement. In many instances these casing seats are set shallower than is optimal due to anticipated hazards such as shallow gas or water flows and wellbore stability issues. Although with the current deepwater drilling model these practices are safe and reasonably efficient, they can limit the depth at which the casing can be set, as compared to the optimal depth with respect to pore pressures and fracture gradients.

The use of current proven Casing While Drilling (CWD) techniques has effectively reduced NPT in several key areas including: flat-time reduction, shallow hazard mitigation, minimized/eliminated lost circulation, and improved cement placement and bond. Additionally, CWD provides the opportunity to push casing seats deeper, thus potentially eliminating contingency strings. Current CWD methods have not been applied to subsea surface casing applications, primarily because of the challenge of simultaneous drilling-in and landing the high pressure wellhead without damaging the seal surfaces on the wellhead housings. Additionally, many wellhead running tools are not designed to carry drilling torque.

This paper discusses the benefits associated with drilling-in the surface casing in a subsea application. Introduced is a new CWD method and enabling technology that can significantly improve this phase of deepwater drilling operations. The complete process of drilling-in and running casing, landing the wellhead, and cementing can be achieved in a single trip. The benefits of CWD and features of the new technology are presented. When compared with current deepwater "best practice" models, an immediate 25% time savings is achievable. This technology also enables the utilization of less expensive floating rigs for cost reduction by batch drilling and setting of surface casing.

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