Managed pressure drilling and cementing
Although managed pressure drilling and cementing are long-established methods, they have only been adopted on the Norwegian continental shelf (NCS) in recent years.
These techniques make it possible to drill formations where the differential between fracturing and pore pressures is so small that traditional drilling methods are inadequate.
Managed pressure drilling and cementing of casing can be used in such cases as:
- reservoirs where pressure has declined because of production
- reservoir zones with overpressure compared with the normal trend
- reservoirs with particularly high pressure and temperature
- reservoirs where particularly long sections must be drilled with the same borehole diameter
These methods adjust formation pressure either by establishing a backpressure with the aid of an enclosed pumping system or by adjusting the fluid level in the drilling riser (also known as a controlled riser level). Using managed pressure drilling and cementing can also increase security, with less loss of fluid to the formation and improved well Control.
The traditional approach to controlling pressure at the drill bit is to add weight material to the drilling mud or to thin it in order to increase or reduce pressure respectively. This takes longer, and is not as exact as managed pressure drilling.
Cementing wells is important both to achieve the necessary barriers and for zone isolation in reservoir sections. If fracturing of the formation because of excessive pressure allows cement to enter it, the risk arises that barriers or zone isolation fail to be established. Managed pressure cementing makes it possible to adjust pressure, which would not normally be possible when pumping a predetermined cement slurry. That increases the likelihood of a successful cement job.
Used on several fields – Gullfaks, Kvitebjørn, Grane, Oseberg and Troll – in addition to exploration drilling.
Gullfaks and Kvitebjørn are the fields on the NCS which have made the greatest use of managed pressure drilling and cementing, and with considerable success. A number of wells on Gullfaks would have been substantially more complicated to drill and cement without this Technology.
Managed pressure drilling has been used for most of the wells on Kvitebjørn in recent years. Before this technology was adopted there, the alternative was to reduce production in order to retain the opportunity to drill more wells. Operator Statoil says that managed pressure drilling on Kvitebjørn has contributed many billions of kroner in additional revenues.
Much use has been made on Troll of managed pressure drilling through zones of reduced pressure by adjusting the fluid level in the riser. This approach has made it possible to drill long sections with a big reduction in fluid loss to the formation.
Managed pressure drilling has been adopted on Valhall in strata above the reservoir for the drilling programme which began in the first quarter of 2017.
A number of other fields have regularly been named as candidates for managed pressure drilling. But the threshold for adopting this method appears high because of the challenges posed.
- Expensive equipment with big footprint
The equipment used for managed pressure drilling occupies considerable space and is expensive to hire. Many drilling rigs (both fixed and mobile) face space challenges, and the cost of making provision for the method can therefore be high.
- Training for use
The method also requires training. This means that the first wells take longer and cost more than those which can be drilled once drilling personnel have gained some experience.
Measures and further development
Developing and implementing managed pressure drilling are making slow progress. Continued development and cost cutting by the companies and the supplies industry are important. Implementing this technology could open the way to a number of profitable drilling targets.
In addition to making provision for managed pressure drilling in modification projects on existing facilities, it is important to plan for using this type of technology when designing new ones.
Adopting managed pressure drilling will also be important for the ability to develop discoveries in a special type of reservoir rock known as karstified carbonates. This contains oil and gas in large cavities, making it difficult to control pressure in order to ensure secure drilling