from Oil & Gas UKCore samplesIf the geologists find something...

from Oil & Gas UK

Core samples

If the geologists find something particularly interesting they can ask for a core sample. A hollow drill, called a core barrel, is attached to the drillstring and as it goes down a core of rock forms inside - a bit like using a giant apple corer! This core sample gives a continuous record of the different layers of rock and therefore more detailed information than the rock cuttings. Collecting a core sample is expensive and time consuming because it involves a complete 'round trip'.

Posters had covered this - but a good reference never hurts.

link:http://www.oilandgas.org.uk/education/students/drilling.cfm