While negative porosity is clearly impossible, the scale is set for an apparent porosity. Any zone with a greater bulk density than a limestone with zero porosity (i.e. calcite, density 2.71 gm/cc) will appear to have "negative porosity."

Can a void ratio be negative?

Void ratio is the ratio of volume of voids to the total volume and thus cannot be negative if we follow the right approach.

What does a porosity of 1 mean?

Porosity is the percentage of void space in a rock. It is defined as the ratio of the volume of the voids or pore space divided by the total volume. It is written as either a decimal fraction between 0 and 1 or as a percentage. For most rocks, porosity varies from less than 1% to 40%.