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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]
(14) \Sigma_g \approx 3
(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

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