DOWNHOLE REBOUND HARDNESS MEASUREMENT WHILE DRILLING OR WIRELINE LOGGING

A method of obtaining a hardness profile of a formation is disclosed. A testing surface in a wellbore impacts the formation to obtain a measurement of formation hardness. A lithological property of the formation is measured and used in determining the rock strength of the formation from the formation hardness. The testing surface may be propelled at the formation a plurality of times to obtain a profile of rock hardness measurements with distance into the formation, including at a surface layer of the formation. Alternatively, the testing surface can be propelled at the formation at multiple energies to obtain formation properties at a plurality of depths into the formation, including at a surface layer of the formation. The rock strength may be used with measurements of geomechanical stress and pore pressure to build a model of the formation in order to develop the formation.