The removal of formations from the well bore (through mechanical means) in, as nearly as possible, an undamaged or physically unaltered state.
In the broad sense, laboratory measurements on core samples furnish data available from no other source. Well logs will continue to play a very important role in well reservoir identification and analysis, but cores will always provide the most accurate information to the geologist, petro physicist and reservoir engineer.
A drill stem test is a procedure for isolating and testing the pressure, permeability and productive capacity of a geological formation during the drilling of a well. The test is an important measurement of pressure behavior at the drill stem and is a valuable way of obtaining information on the formation fluid and establishing whether a well has found a commercial hydrocarbon reservoir. see attachment for additional wording/information