The density porosity is usually abbreviated DPHI 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,. |