In places where overburden strata are mixed, or when their drill ability is unknown, it is difficult for the driller to decide what tools to use in order to get best overall results without risking the loss of the equipment in the hole.
In places where overburden strata are mixed, or when their drill ability is unknown, it is difficult for the driller to decide what tools to use in order to get best overall results without risking the loss of the equipment in the hole.