During the second half of 2018, an operator faced significant downhole issues during exploration drilling on a semisubmersible rig in ultra-deepwater Nova Scotia. While these challenges would have made this well a candidate for the use of traditional surface backpressure managed pressure drilling (MPD) technology, the predrill forecast did not indicate the need for MPD, and during execution, it was not practical to install MPD because of the required time and detailed engineering to retrofit the rig.
During the original attempt to drill this well, the operator was forced to abandon the 12 1/4- × 14 1/2-in. hole section after mud losses, followed by wellbore breathing and associated gas events from the mud flowback. The well was undrillable with conventional methods, and the wellbore was plugged back and sidetracked. On the sidetrack, continuous circulation technology was implemented to help maintain a more constant bottomhole pressure, navigate the narrow drilling margin between pore pressure and fracture gradient, and help prevent wellbore breathing and associated gas on connections.
The planning and execution of this technology that allowed the operator to successfully drill through previously difficult targets are discussed, along with lessons learned for future wells. Overall, more than 30 connections were performed, with an average of 600-gal/min connection flow rate with synthetic oil-based mud over the two hole sections.