Shales | Clays and Minerals
Shales are the most abundant kind of all sedimentary rocks accounting for around 60% of the stratigraphic column. As such, most of the time spent drilling oil wells is spent drilling through shales. Clay minerals account for about 5060 wt.% of most shales and are often responsible for many of the problems encountered when drilling through shales. Shales are now also a focus .