Coiled tubing drilling system placed on the seabed

Abstract

In recent years, the demand for more cost effective solutions within the oil industry has been huge. Low oil prices mean that innovation and new intelligent solutions are required to get profit. The focus is on reducing costs and increasing efficiency.

Coiled tubing drilling has proven to be a cost-effective solution in many situations. With coiled tubing drilling, the drill string is coiled around a large drum, where the drill bit at the end is driven by the mud. A big advantage is that the operation only needs an intervention vessel instead of a conventional drilling rig with risers. It is very cost effective as it both reduces costs sharply and is much quicker to rig up.

If you should drill offshore today is the coiled tubing drilling system placed on a vessel. The purpose of this thesis is to see if it is possible to develop the concept of coiled tubing even a step further. This thesis will examine the possibility of having the coiled tubing system on the seabed to make the process, even more, cost effective. The master thesis presents a concept of how this can be done. There are many different challenges by having the installation on the seabed, but this task will primarily focus on the fatigue the drill string will get due to regularly strain.

As the installation is placed under water, the drill string must be of other materials than the low carbon steel used today. One requirement is that the material should be resistant to corrosion. Stainless steel and duplex steel are two excellent candidates for this purpose and will be tested. Low carbon steel is tested in order to compare against what is used in current drill strings.

Low cycle fatigue tests are performed on specimens of various materials. A test like this stretches the specimen back and forth in cycles until it breaks. The strain was varied between 2-3%, which is completely normal values in today's operations. It will then show how many cycles the stainless materials can withstand compared with low-carbon steel.