Formation evaluation neutron porosity

In the field of formation evaluation, porosity is one of the key measurements to quantify oil and gas reserves.

As hydrogen is fundamentally associated to the amount of water and/or oil present in the pore space, measurement of neutron population within the investigated volume is directly linked to porosity.

Certain effects, such as lithology, clay content, and amount and type of hydrocarbons, can be recognized and corrected for only if additional porosity information is available, for example from sonic and/or density log.

The quantitative response of neutron tool to gas or light hydrocarbon depends primarily on hydrogen index and "excavation effect".

The tools usually have two detectors (or more) with different spacings from the source to produce ratio of count rates, which theoretically reduce borehole effects.

To boost the charge produced by the interaction between helium and a neutron, a high voltage is applied to the anode of the counter.