The density porosity is usually abbreviated DPHI on or PHID on log panels and denoted as in equations. The key measurement is the bulk rock density (log name RHOB) from Litho-Density Tool.The key model parameters are: | rock matrix density | | shale density | | pore-saturating fluid density | | mud filtrate density | | LaTeX Math Inline |
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| body | \{ \rho_w, \, \rho_o, \, \rho_g \} |
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| formation water, oil, gas density | | a fraction of pore volume invaded by mud filtrate | | LaTeX Math Inline |
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| body | \{ s_w, \, s_o, \, s_g \} |
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| original water, oil, gas reservoir saturations |
The values of and are calibrated for each lithofacies individually and can be assessed as vertical axis cut-off on cross-plot against the lab core porosity and shaliness . The model also accounts for saturating rock fluids with fluid density . In overbalance drilling across permeable rocks the saturating fluid is usually mud filtrate. In underbalance drilling the saturating fluid is identified from resistivity logs.
The total density porosity equation is: | LaTeX Math Block |
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| anchor | phie_rhob |
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| alignment | left |
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| \phi_d = \frac{\rho_B - \rho_m}{\rho_{fl}-\rho_m} |
The effective density porosity equation is:
| LaTeX Math Block |
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| anchor | phie_rhob |
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| alignment | left |
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| \phi_{ed} = \phi_d - \frac{\rho_{sh}-\rho_m}{\rho_{fl}-\rho_m} \cdot V_{sh} |
The fluid density is calculated in-situ using the following equation:| LaTeX Math Block |
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| \rho_f = s_{xo} \rho_{mf} + (1-s_{xo}) ( s_w \rho_w + s_o \rho_o + s_g \rho_g ) |
The matrix density is calculated from the following equation: | LaTeX Math Block |
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| \rho_m = \sum_i V_{m,i} \rho_{m,i} |
where – volume share of the i-th matrix component, – density of the i-th matrix component,. | 