Increasing the value of deepwater wells Kenneth J. Kotow, Steven M. Rosenberg, Nitin M. Kulkarni and James P. Wakefield, Subsea Drive LLC, USA, explain how deepening the structural casing in the riserless section using casing drilling can lead to improved well integrity and economics.
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significant improvement in deepwater well integrity and value can be accomplished by deepening the structural casing creating its dual functionality. This results in the structural casing providing both axial and bending loading requirements and having a stronger casing shoe strength to drill any subsequent shallow drilling hazards. This, in turn, reduces at least one casing string in the riserless section to place the high-pressure wellhead housing (HPWH) casing significantly deeper than is possible with conventional methods. The result is fewer casing strings to reach planned well depths with placement of larger casing diameters with larger annuli deeper than current practice allows (Figure 1). This improves the likelihood of attaining the deepwater well objectives by enabling larger drilling operating pressure windows to minimise the risks associated with the loss circulation/well influx cycle. The method proposed for deepening the structural conductor is casing drilling technology utilising the Subsea Drive Casing
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Drilling System. Casing drilling technology facilitates drilling casing to deeper depths than are currently possible with the practice of jetting, while mitigating the hazards of shallow drilling with a single trip. Casing drilling on land or offshore is not new, having been applied frequently to improve drilling operations through greater drilling efficiency and mitigation of drilling hazards. However, casing drilling has never been used in a subsea environment since the technology was not available. Subsea Drive, LLC has developed the concept to deepen the structural casing to improve deepwater well design, using casing drilling as the means to achieve the objectives. The deepened structural casing is part of a specially designed system – which includes casing with high torque capacity connections, casing bit, cementing inner string and a running/drilling tool – called the Subsea Drive. On top of the casing of this system is the low-pressure wellhead housing (LPWH), which is out of the torque path. This system is run on drill pipe to the seafloor with rotation
