Seawater injected into the Ekofisk reservoir

Senior tool pusher Eyvind Normann took part in this work, and relates what happened:

We started by establishing a plan for how the wells in the K project would look. A steel template was then constructed and placed on the seabed. This formed part of the base which the 2/4 K structure would later fit onto.

We then secured the Dyvi Beta jack-up, which stood over the template alongside Ekofisk Bravo and drilled for a couple of years until 2/4 K was ready. The platform jacket was then installed over the template and the topsides placed on it.

This project was an unparalleled success. We drilled 28 wells in two and a half years. The level of activity was incredible.[REMOVE]Fotnote: Eyvind Normann interviewed by Kristin Øye Gjerde, 23 June 2003.

The accommodation module was lifted onto 2/4 K on 6 August 1986, and hook-up work could proceed at full speed ahead until late 1987.

On 28 December of that year, treated seawater could be injected from the platform through well K-30. K-4 was ready a few days later, and the remaining injection wells followed one after the other.

These provide waterflooding in the actual Ekofisk structure. The longest measures just over seven kilometres, and all are drilled to the reservoir depth of about 3 000 metres.

Ekofisk comprises two reservoir zones. Known as the Ekofisk formation, the uppermost is of Danian age and dates back 61-66 million years. The lower Tor formation is of Maastrichtian age (late Cretaceous) from 66-72 million years ago.

These two structures are separated by a tight (impermeable) zone 20-30 metres thick. Waterflooding takes place mainly in the Tor structure.

Seawater is sterilised on 2/4 K with a form of ultraviolet radiation and various chemicals are then added. The amounts of these have been reduced over time.

Seawater contains microbes, bacteria and oxygen. If sulphur-producing algae, for example, gain access to oxygen at warm temperatures, the resulting corrosive substance can consume steel and quickly destroy the whole reservoir. So complete sterilisation is important.