NEUTRON SOURCE EFFECTS IN WELL LOGGING

In this section of the website, the origins of micro geophysical modeling are touched upon and four LVPM OUTPUTS - fast neutron slowing down length (Ls), thermal neutron diffusion coefficient (D), thermal neutron diffusion length (L), and thermal neutron capture cross section (SIGMA) - are seen in their native habitat.

Figure 1, taken from US Patent 3,906,224 and a full copy, are provided below. This Figure forms the starting point for a discussion of the effects that different neutron sources and their energies and modes of operation have on nuclear well logging tools.

Figure 2 was generated by LVPM: it forms the basis for a novel way to measure neutron porosity with a neutron generator-based logging tool that has both good porosity measurement sensitivity and good count rates. The genesis of this method is US Patent 3,818,225 and a copy is also provided below. The main idea is to directly measure the thermal neutron diffusion coefficient and then use the relationships shown in Figure 2 to obtain neutron porosity.