Page 199 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

168 Reservoir Engineering

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@sN~~~~, Porosity Index (pu)
Neutron
(Apparent Limestone Porosity)
Figure 5-95. Chart for finding porosity and matrix composition from an
FDC-SNP log combination in fresh water [199].
differences in the local magnetic fields. Moreover, each proton precesses at a
slightly different frequency, depending on the kind of fluid it occurs in. This
disharmonic relationship makes it possible to differentiate between free water
and free oil in a reservoir [213].
Three log modes can be presented
1. Normal mode--consists of the free fluid index (FFI) in percent obtained
from a polarization time of two seconds, the Larmor proton frequency
(LFRE), the decay-time constant (or longitudinal relaxation time) of the
signal (T,) and a signal-to-noise ratio (STNR).
2. Continuous mode-gives three free fluid index (FFI) readings taken at
polarization times of 100, 200, and 400 ms, respectively, two longitudinal
relaxation times (T, and T,), and a signal-to-noise ratio (STNR).