The tool answers to all the hydrogen atoms without discrimination, it will thus take also into acount of the hydrogen related to the mineralogical nature of the formation. While choosing like reference 100% for fresh water, and 0% for a compact limestone (CaCO³=0 hydrogen) we will obtain a scale varying from 0 to 100 which in a limestone porous environment will represent porosity. We will speak about a limestone calibrated neutron.

Scale: cps, porosity, density

The matrix won't answer the same way. We can also make calibrations compared to the sandstone or dolomite. In this case in heading we will find "sandstone matrix" or "dolomite matrix".

The Petroleum tools are all calibrated in the test borehole of American Petroleum Institute of Houston. The logs coming from various companies are thus comparable. The Petroleum logs are calibrated in scale compatible with three units of porosity corresponding to 0.5 gr/cm³ for a division, and increase in porosity towards the left. It is necessary to pay attention, these units of porosity are more an indication than a true porosity.

A limestone calibrated neutron will be pessimistic opposite sandy formation and optimistic opposite dolomite formation. For each tool there are correction Charts which make it possible to pass from limestone to sandstone or limestone to dolomite.