ABSTRACT
Diamond drill bits frequently cut a core along with routine hard rock drilling. Information from core samples is essential to the proper evaluation of both petroleum and non-petroleum formations. The analysis of core samples tells much which cannot be determined in other ways. As important is their function as the calibration standard for other methods, such as wireline geophysical logs. Correlation with other methods is important, as is combination of core data with that from other methods. As the cutting proceeds, the uncut center of the rock, or core, is pushed up into the coring assembly, through the open center of the bit. Hard-rock sidewall coring uses a motor and/or a hydraulic system to position and rotate a small coring bit into the wall of the hole. In oceanography and in well drilling, a drop corer is sometimes used. Cores are severely flushed by the drilling mud before, during, and after the drilling operation.
