It means measurements made both during and after the drilling. If you replace et by ou it would have meant measurement made either during or after the drilling.

You can consider this as a shortcut for the whole (quite redundant) expression :

Mesures pendant forage et mesures après forage

But, granted, each single measurement is made during OR after the drilling, and that’s an exclusive one.

Like saying un champ de fleurs bleues et blanches, which of course doesn’t imply two-colored flowers.