| Popis: |
In recent years, with the availability of high-performance automated drilling systems, the drilling challenge has moved to even further critical operations involving deepwater and ultra-deepwater environments, HPHT applications, anomalous pressure regimes and reduced margins between pore and fracture gradients. Even though prevention comes first, achieved through best practices and master operating attitude, the availability of tools and procedures to cope with critical events is very important. Nowadays, whenever necessary, a best oil industry practice is represented by Managed Pressure Drilling Systems. These systems consist in a set of surface tools and equipment that enhance drilling capacity and grant a safe drilling process. In case of emergency, the reaction is usually fully devoted to these systems and the blowout preventer (BOP). For many years, the possibility of introducing both static and dynamic safety barriers directly into the well has been considered to limit the intensity of kick events and achieve a consistent increase of safety. This paper describes two field experiences (in the US and Italy) achieved with downhole isolation packer subs that can be integrated in the drillstring to operate in an open hole as well as above the last casing shoe. Risk-assessment advantages obtained with this technology are also analyzed and reported. As dynamic barriers, downhole isolation packers complement conventional BOP systems and work in combination with them, to: stop a kick close to the bit, improve well integrity and optimize well control procedures. In case of a kick, while closing the surface BOP is according to standard practices, a downhole isolation packer, as part of the drillstring, can be activated by means of a downlink. The well annulus will be shut in, trapping the kick below the tool, thus enabling it to condition the mud above it and to bullhead the kick back into the formation. |
