Extended reach drilling

The rig in one place, the reservoir many kilometres away: wells often need to be drilled over huge distances to reach oil and gas deposits. Extremely long wells – extended reach drilling – are a demanding challenge for our personnel and the equipment they use.

We work our way to such a reservoir in much the same way as a doctor uses an endoscope to examine a patient's internal organs. Extended reach drilling is particularly suitable for producing oil or gas from an onshore site. RWE Dea operates Mittelplate Drilling and Production Island in the Wadden Sea National Park off the coast of Schleswig-Holstein in North Germany. From Mittelplate, the only drilling rig authorised to operate in this National Park, we can drill production wells of up to seven kilometres in length. To further protect the environment of this unique mud flats landscape, all future production wells will be drilled from an onshore site – technically speaking, a highly demanding undertaking. Two preconditions need to be met: the reservoir cannot be too far from the shore and the rock formations must not be heavily fissured. RWE Dea has already drilled 10 km wells and lengths of more than 15 km are being planned. We are relying on extended reach drilling to develop the reservoirs from onshore sites for our drilling operations in the Caspian Sea.

The distances involved with extended reach drilling mean that a drill string rotating through rock over thousands of metres is subject to particularly high torque and grinding forces. To avoid downtime or malfunction, friction needs to be minimised during the drilling operations therefore the drilling crew constantly flush the well with special drilling fluids (aka mud) and rotate the drill string. Without this rotating motion only about 8 km can be drilled but with rotation we have achieved 10 km. Also using this method, a distance of 12.345 km has been achieved and this is currently the longest well in the world located on the Russian island of Sachalin.

If you don't go forward, you go backwards – and that's why we are involved in projects that aim to optimise the drilling technology and may well achieve a new record in extended reach drilling. In Norway, we and a partner company are developing a new drilling method in which the fine particles of rock produced during drilling (so-called cuttings) are not removed from the borehole by traditional means (via the annulus) but through the inside of an innovative double drill string. This ensures that the annulus does not get bunged up and also enables better control on the pressure and volume flows.

There is also scope for improvement in the weight of the drill string. It needs to be robust, but at the same time as light as possible – the lighter and more voluminous it is, the lower the friction losses. We try to counteract such friction losses through the use of a heavyweight drilling fluid. This buoys up the drill string, which swims in the fluid and friction is reduced. To this end, we are also working on an aluminium drill string. In a separate research project we are developing a new carbon fibre-based plastic material that is both very strong yet lightweight. One day, it could well replace the steel drill string in use today.