Qatif-Nphi

UCS = 23018e(–4.79 ´ Nphi)

where

23018 is in psi.

4.79 is unitless.

Nphi is the neutron log value expressed as a fraction.

This equation is derived from a core-log correlation of multistage triaxial test results on 13 limestone samples and a neutron log in a well in the Middle East. The core porosity range is between 4.8% and 19.7% with a 13.5% average. The reported UCS values range between 4,900 and 22,500 psi. There is a major concern about the data set due to the test procedures and the reported UCS may not represent the actual uniaxial compressive strength of the samples. In addition, log data were not corrected for possible hydrocarbon and shale effects.