Neutron count in time interval
\tau = [\tau_1, \, \tau_2]
Neutron Porosity
(1) |
N_{near}[\tau] = \int_{\tau_1}^{\tau_2} N_{near}(t) dt |
(2) |
N_{far}[\tau] = \int_{\tau_1}^{\tau_2} N_{far}(t) dt |
(3) |
N2F = \frac{ N_{near}[\tau]}{N_{far}[\tau]} |
Diffusion Correction
(4) |
\phi_T = N2F[\tau] + \Delta_{\tau}(\phi_N) |
Neutron Sigma
(5) |
N_{near}(t) = N_{near}(0) \exp ( - t \, \Sigma_{near} ) |
(6) |
N_{far}(t) = N_{far}(0) \exp ( - t \, \Sigma_{far} ) |
Diffusion Correction
(7) |
\Sigma_{near} = \Sigma_{frm} + \Delta_{near}(\phi) |
(8) |
\Sigma_{far} = \Sigma_{frm} + \Delta_{far}(\phi) |
Neutron Saturation
(9) |
\Sigma_{frm} = (1-\phi) \, \Sigma_m + \phi \, ( \Sigma_w \, s_w + \Sigma_o \, s_o +\Sigma_g \, s_g) |
(10) |
\delta \Sigma_{frm} \approx +/-1.5 c.u. |
(11) |
\Sigma_m = \sum_k \Sigma_k |
(12) |
\Sigma_o \approx 18 \quad 11 < \Sigma_o < 21 |
(13) |
\Sigma_w = 21 + 0.05 * Sal[\rm ppk] |
(15) |
\Sigma_{sh} \approx 40 \, c.u. |
(16) |
\Sigma_{ls} \approx 7 \, c.u. |
In case of two-component sandstone-shale model:
(17) |
\Sigma_m = (1-V_{sh}) \, \Sigma_{snd} + V_{sh} \, \Sigma_{sh} |
In case of two-component limestone-shale model:
(18) |
\Sigma_m = (1-V_{sh}) \, \Sigma_{lms} + V_{sh} \, \Sigma_{sh} |
TSCN, TSCF, NPHI, SIGMA
References
SPE162074 – Memory Pulsed Neutron-Neutron Logging