Reaming is required when the hole size becomes less than the...

Reaming is required when the hole size becomes less than the drilling bit size. This occurs when the shales/clays swll on contact with the drilling mud or when the shales are overpressured.

The latter is more likely in the Cretaceous in the Mauritanian Salt Basin.

On the matter of the section with the shows, I would have expected that pressure measurements and fluid sampling could have thrown light on the situation. Perhaps the Chinese logging company did not have this equipment around. However, there is hope because stimulation of tight formations onshore is cheaper than offshore - see what the smaller companies are doing in the Eromanga Basin in South Australia.

Drilling in the Taoudeni Basin is what I am looking forward to!

Cheers,

Oli