Core-based strength logs are a non-destructive solution to probe relative strength of cores over large
depth intervals. Two primary methods used to measure core strength are Brinell hardness and ultrasonic
velocity. Both are important in identifying the weakest interval within the formation.
The Brinell hardness test is performed by applying measured load to a spherical steel-ball (indenter) that is in
contact with the sample. The depth of ball penetration is recorded along with the applied load. The hardness value
is determined from the ratio of applied load to the indentation area and is expressed as kg/mm2.
Sonic Velocity is a direct indication of the degree of cementation for the rock, which, in turn,
controls the rock strength. Sonic velocities are an industry standard for indirect determination of strength.
Unconfined compressive strength can be indirectly determined from the acoustic velocities that are measured across
the diameter of whole cores or slabbed cores (i.e., butt sections) as well as routine core plugs.
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