Application of dynamic pressure management technologies for successful drilling of the «undrillable» well at Severo-Danilovskoe field

Background. Problems, described in this paper, related to narrow equivalent circulation density (ECD) window which associated with problems such as formation fluid influx, drilling fluid losses, hole stability issues and etc. Another problem could be related to undrillable well conditions. Conventional drilling through undrillable zone in most cases will lead to simultaneous well control and losses. To overcome such well conditions at Severo-Danilovskoe field operator performs several well control operations and cement bridge installations, but in 90% cases it’s unsuccessful.

The aim. To optimize the process of drilling in complex geological conditions at Severo-Danilovskoe field a dynamic pressure drilling technology was introduced. It included specialized equipment, software, and adaptive engineering approach for ECD optimization in narrow mud weight window environment as well as for drilling through undrillable zones.

Materials and methods. An adaptive approach for flexible transition for one DPM technique to another was developed for expected well complexity. For drilling in narrow mud weight window managed pressure drilling (MPD) technique was applied, and for drilling without window — pressurized mud cap drilling technique (PMCD). To overcome unexpected conditions that were met while drilling (abnormal drilling fluid foaming, wellbore ballooning) unconventional well testing performed in order to examine well behavior at different overbalance/ underbalanced conditions.

Results. Application of dynamic pressure control technology and the development of unconventional procedures made it possible to successfully drill a well with undrillable conditions. The implemented set of well tests using DPM equipment made it possible to design the optimal methodology for killing the well and carrying out tripping operations with the drilling BHA and casing string.

Conclusions. Successful experience of application of DPM technology, as well as methods and procedures developed within this project objectives, could be used to simplify the well construction in difficult environment. This approach could reduce the cost of wells with naturally fractured carbonate reservoirs where presented a high risk of conditions together with abnormal foaming of the drilling fluid and wellbore ballooning.

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