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