PETROPHYSICS POROSITY TOOL: A COMPREHENSIVE CALCULATOR

 1. Porosity

Simple equation for total porosity:

Total porosity (Φ): Volume of void space (Vp): Bulk volume of the rock (Vb):

2. Porosity from density log 

Bulk density (ρ_bulk): Porosity (Φ): Matrix density (ρ_matrix): Fluid density (ρ_fluid):

Porosity (Φ_density): Bulk density (ρ_bulk): Fluid density (ρ_fluid): Matrix density (ρ_matrix):

Fluid density if the formation is the hydrocarbon bearing:

Fluid density (ρ_fluid): Density of the mud filtrate (ρ_mf): Saturation of the mud filtrate in the invaded zone (Sxo): Hydrocarbon density (ρ_hc):

Total porosity estimate:

Bulk density (ρ_bulk): Porosity (Φ): Fluid density (ρ_flu): Shale density (ρ_sh): Volumetric estimate of shale proportion (Vsh): Matrix density (ρ_matrix):

Correct the total porosity to the effective porosity:

Effective porosity (Φ_e): Total porosity (Φ_t): Shale density (Φ_sh): Volume of shale (V_sh):

3. Porosity from neutron-density log

Effective porosity (Φ_e): Neutron porosity log readings (Φ_Neutron): Density porosity log readings (Φ_Density): Volume of shale (V_sh): Shale density (Φ_nsh): Density of shale (Φ_dsh):

4. Porosity from sonic log

The linear interpolation (Willye et.al., 1956):

Total porosity from sonic log (Φ_sonic): Acoustic travel time log measurement (Δ_t): Matrix transit time which depend on the lithology of the rock (Δ_{t matrix}): Pore fluid transit time (Δ_{t fluid}):

Raymer-Hunt-Gardner(RHG) transform:

Total porosity (Φ): Acoustic travel time log measurement (Δ_t): Matrix transit time which depend on the lithology of the rock (Δ_{t matrix}): Pore fluid transit time (Δ_{t fluid}):

5. Shale volume (Vsh) from neutron density

Volume of shale (V_sh): Neutron porosity log (Φ_Neutron): Total porosity from density log (Φ_Density): Neutron porosity of shale (Φ_nsh): Density porosity of shale (Φ_dsh):

6. Gamma Ray

Expectation of the API unit log reading of a shale:

Gamma ray total (GR_total): Uranium (U): Thorium (Th): Kalium (K):

Analysis of the North American shale composite (NASC) reference standard (Gromet et.al., 1984):

Gamma ray total (GR_total): Uranium (U): Thorium (Th): Kalium (K):

7. Shale volume (Vsh) from Gamma Ray

Volume of shale (V_sh): Gamma ray (GR): Gamma ray maximum (GR_max): Gamma ray minimum (GR_min):

Larionov equation on Tertiary rock:

Volume of shale (V_sh): Gamma ray index (GRI):

Larionov older rocks:

Volume of shale (V_sh): Gamma ray Index (GRI):

If clay volume was the issue:

Volume of clay (V_cl): Volume of shale (V_sh):

Steiber equation:

Volume of shale (V_sh): Gamma ray index (GRI):

Volume of shale (V_sh): Gamma ray index (GRI): (c):

c = 1 → Vsh with the gamma ray index (GRI)

c = 2 → older rocks

c = 3 → Tertiary rocks 

Reference:

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