Tight formations

Basalt can form reservoirs for oil and gas on the NCS if it contains open fractures and a certain number of cavities. Such rocks have been identified in the Norwegian Sea, but have not yielded discoveries. Migmatites and basalt intrusion can be observed at Håhammeren along the Hafrs Fjord outside Stavanger.

| Christian Magnus and Janka Rom (Photo)

Photo: Janka Rom

Migmatite is a rock formed under high pressure and temperature deep in the Earth’s crust, and migmatitic gneiss is a variant which has partially melted. That gives it a veined and marbled appearance.

This rock often comprises dark, wavy laminations and bands (older material) encased in a light granitic matrix (more recent). The latter can be formed by the injection of magma, by partial melting of the rock in situ, or by a reaction in the solid phase.

After the migmatite was formed, basalt (dark rock) has intruded. Formed through volcanic eruptions fairly directly from the Earth’s mantle, this is a finegrained lava.

Dark and light crystals (pictured) lie in and near the centre of the basalt intrusions because slow solidification gives them time to form. That has occurred at low temperature and pressure. The contact with the migmatite is more fine-grained because of cooling.

 

Norwegian Continental Shelf no.2-2015

Main page - Contents
Bente Nyland on the NCS: Glass is half-full
The interview: Petroleum minister calls on companies to invest
Thinking outside the box made Maria’s development possible
Special report: 50 years
Norway’s offshores sector safer than before
Safety carries a cost
Seeking to cut documentation
Eldar Myhre and son Aslak discuss what oil has done with Norway
NPD profile: Diskos database crucial for exploration success
Making huge volumes of offshore data available
Adding up to acclaim Geology: Many benefits for society
www.norskpetroleum.no: Find facts about the NCS

Topics: Geology

01.12.2015