One of the saturation from resistivity models:
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| LaTeX Math Block |
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| anchor | Archie |
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| alignment | left |
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| \frac{1}{R_t} = \frac{\phi_e^m \, s_w^n }{A R_w} \quad \Rightarrow \quad s_w = \Big ( \frac{A}{\phi_e^m} \; \frac{R_w}{R_t} \Big) ^{1/n} |
where
| formation water saturation |
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| effective porosity |
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| specific electrical resistivity from OH logs |
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| specific electrical resistivity of formation water |
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| dimensionless constant, characterizing the rock matrix contribution to the total electrical resistivity | 0.5 ÷ 1, default value is 1 for sandstones and 0.9 for limestones |
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| formation matrix cementation exponent | 1.5 ÷ 2.5, default value is 2 |
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| formation matrix water-saturation exponent | 1.5 ÷ 2.5, default value is 2 |
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Archie model is usually used in: - high permeable clean sands with low or no shaliness
- high permeable clean limestones with low or no shaliness
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