Calculate Sonic Porosity - Shale Corrected (Dewan, 1983)

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Sonic Derived Porosity- Shale Corrected - Dewan (1983)

Dewan (1983) proposed a simple equation to make the shale correction to the value obtained from sonic derived porosity, where he considered shale volume and the sonic porosity in a nearby shale at the depth of the study area. The equation is the following:

Where:
• ɸSe= effective (shale-corrected) sonic porosity
• ɸS= sonic porosity
• ɸSsh= sonic porosity in a nearby shale
• Vshale= shale volume

Calculate Sonic Derived Porosity - Shale Corrected- Dewan (1983)
ɸs: Decimal		Vsh: Decimal
ɸssh: Decimal

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Calculate Sonic Porosity - Shale Corrected (Dresser Atlas, 1979):

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Sonic Derived Porosity- Shale Corrected - Dresser Atlas (1979)

Dresser Atlas (1979) created an equation to calculate the shale corrected sonic derived porosity, using Wyllie (et al., 1958) equation as the basement, and considering the shale volume and sonic porosity in a nearby shale values. The expression is the following:

Where:
• ɸSe= effective (shale-corrected) sonic porosity
• ɸS= sonic porosity
• ɸSsh= sonic porosity in a nearby shale
• Vshale= shale volume
• Δtlog= interval transit time of the formation (from the sonic log)
• Δtma= matrix interval transit time
• Δtfl= fluid interval transit time
• Δtsh= interval transit time in a nearby shale

Calculate Sonic Derived Porosity - Shale Corrected - Dresser Atlas (1979)
Δtlog: µs/ft		Δtma: µs/ft
Δtfl: µs/ft		Δtsh: µs/ft
Vsh: Decimal

Made by Henry Herrera

Calculate Sonic Porosity - Hydrocarbons Effect

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Sonic Derived Porosity- Hydrocarbons Correcction

Hydrocarbons generate an effect at the time of estimating porosity from sonic well log tools. Oil and gas create an increasing or decreasing effect of the real value of porosity. That is the reason why sonic derived porosity values must be multiplied by a correction factor depending on the type of hydrocarbon.

Sonic Derived Porosity- Oil Effect

Where:
• ɸs= Sonic Log Derived Porosity

Calculate Sonic Derived Porosity- Oil Effect
ɸs: Decimal

Sonic Derived Porosity- Gas Effect

Calculate Sonic Derived Porosity- Gas Effect
ɸs: Decimal

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Calculate Sonic Porosity - Unconsolidated Formations

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Sonic Porosity- Unconsolidated Formations

To calculate sonic porosity for unconsolidated formation, we can start by getting the product of the Wyllie et al. (1958) sonic porosity equation with the inverse expression of a compaction factor. The equation is the following:

Where:
• ɸs= sonic porosity
• Cp= compaction factor
• Δtma= matrix interval transit time
• Δtlog= interval transit time of the formation (from the sonic log)
• Δtfl= fluid interval transit time

Calculate Sonic derived Porosity - Unconsolidated Formations
Δtlog: µs/ft		Δtma: µs/ft
Δtfl: µs/ft		Cp:

Compaction Factor (Cp)

Compaction factor is calculated from the following equation, which takes into account the sonic porosity at a nearby shale:

Where:
• Δtsh= interval transit time in a shale adjacent to the formation of interest
• C= a constant which is normally 1.0 (Hilchie, 1978)

Calculate Compaction Factor (Cp)
Δtsh: µs/ft		C:

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Calculate Sonic Porosity - Raymer et al. (1980)

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Porosity - Sonic Log- Raymer et al. (1980)

Other way to calculate sonic derived porosity is through the Raymer-Hunt-Gardner (RHG) equation (Raymer et al., 1980), which calculate it using matrix and sonic log values, and it is expressed the following way:

Where:
• ɸs= sonic-derived porosity
• Δtma= interval transit time in the matrix
• Δtlog= interval transit time in the formation

Calculate Sonic Derived Porosity - Raymer et al. (1980)
Δtlog: µs/ft		Δtma: µs/ft

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Calculate Sonic Porosity - Wyllie et al. (1958)

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Porosity - Sonic Log (Wyllie et al., 1958)

The calculation of sonic derived porosity, can be done from the time average Wyllie (Wyllie et al., 1958) equation, which is expressed the following way:

Where:
• ɸS= sonic porosity
• Δtma= matrix interval transit time
• Δtlog= interval transit time of the formation (from the sonic log)
• Δtfl= fluid interval transit time

Calculate Sonic Derived Porosity
Δtlog: µs/ft		Δtma: µs/ft
Δtfl: µs/ft

Made by Henry Herrera