Advanced Rock Properties – Core-Based Strength Logs
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.
Benefits of Core-Based Strength Logs:
- ASTM and industry-wide standard tests (Brinell hardness & acoustic velocity) used to determine UCS data versus depth
- Full diameter of core is tested by bench top ultrasonic rather than just the top surface (greatly reduces data scattering)
- High resolution logs with multiple rock mechanical parameters (Vp, Vs, Ed, UCS, BH)
- Non-destructive strength profile versus depth
Brinell Hardness Test
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.