Theory of Neutron Logging I

Abstract

An analytical theory of epithermal neutron logging is presented. One‐group diffusion theory is applied to the slowing down of neutrons from a point fast neutron source in infinite continuous media, in a single cylinder, and in concentric cylinders representing a fluid‐filled borehole and the surrounding formation. Numerical results are given for the epithermal neutron flux in a water‐filled hole six inches in diameter, passing through limestone of 10 percent or 30 percent porosity. Preliminary semiquantitative agreement is obtained with the relative response of a commercial logging instrument in the range of 10 to 100 percent porosity.

Fast modeling of borehole neutron porosity measurements with a new spatial transport-diffusion approximation

“…We assume that FSF perturbations due to changes in formation HI from a homogeneous background case B can be described by diffusion. Therefore, we invoke a modified one-group, timeindependent neutron diffusion model for nonmultiplying systems (Tittle, 1961) given by…”

Leg 75 Methods for Laboratory-Measured Physical Properties, Gearhart-Owen Well Logs, and the Uyeda Downhole Temperature Probe

“…With the proper matrix correction, the tool is a qualitative indicator of porosity. The tool's principal assumptions and precautions are discussed in Tittle (1961) and Lynch (1962). The depth of investigation and vertical resolution is on the order of 33 cm, depending on logging speed, porosity, and type of formation.…”

K-Division Experimental Work. Part I. Geophysics Research for Underground Explosion Technology.

“…{-il) almost eliminated the chemical effects seen by Tittman. In general, it appears that the method of measuring hydrogen content with a single detector and fitting to Eqs. (39) and (41) will probably be usable provided some medium-chemistry correction is made. The ratio method with four de tectors is also promising.…”