Changes

===Compensated neutron===

===Compensated neutron===

Compensated neutron devices measure the hydrogen index of the formation using a radioactive neutron source that bombards the formation with fast-moving neutrons. Neutrons collide with atoms of the formation, transferring their energy through these collisions. The most efficient transfer of energy occurs with hydrogen atoms because the mass of hydrogen is approximately the same as the mass of a neutron. Two detectors count the number of deenergized (thermal) neutrons returning from the formation. The ratio of the detector count rates is primarily related to the hydrogen index or the apparent water-filled porosity.

Compensated neutron devices measure the [[hydrogen index]] of the formation using a radioactive neutron source that bombards the formation with fast-moving neutrons. Neutrons collide with atoms of the formation, transferring their energy through these collisions. The most efficient transfer of energy occurs with hydrogen atoms because the mass of hydrogen is approximately the same as the mass of a neutron. Two detectors count the number of deenergized (thermal) neutrons returning from the formation. The ratio of the detector count rates is primarily related to the hydrogen index or the apparent water-filled porosity.

The source and detectors are mounted in a mandrel that, ideally, is pressed against the borehole to minimize the influence of the high apparent porosity of the borehole. This measurement is very sensitive to tool standoff, hole size, temperature, and salinity. Environmental corrections are highly recommended before attempting to interpret results. Gas has a very low hydrogen index compared to water, which causes the tool to report abnormally low porosities in gas-bearing formations. When used in conjunction with density measurements, gas-bearing intervals are often easy to identify. A typical presentation of a compensated neutron measurement is shown in the log in [[:Image:basic-open-hole-tools_fig2.png|Figure 2]].

The source and detectors are mounted in a mandrel that, ideally, is pressed against the borehole to minimize the influence of the high apparent porosity of the borehole. This measurement is very sensitive to tool standoff, hole size, temperature, and salinity. Environmental corrections are highly recommended before attempting to interpret results. Gas has a very low hydrogen index compared to water, which causes the tool to report abnormally low porosities in gas-bearing formations. When used in conjunction with density measurements, gas-bearing intervals are often easy to identify. A typical presentation of a compensated neutron measurement is shown in the log in [[:Image:basic-open-hole-tools_fig2.png|Figure 2]].