The image above represents the gas pore volume.

To compute for the gas pore volume, three essential parameters are needed and these parameters are **Initial Gas FVF (B _{gi}), Initial Water Saturation (S_{wi}) and Initial Gas in Place (G)**.

The formula for calculating the gas pore volume:

(PV)_{g} = ^{GBgi} / _{1 – S}_{wi}

Where;

(PV)_{g} = Gas Pore Volume

B_{gi} = Initial Gas FVF

S_{wi} = Initial Water Saturation

G = Initial Gas in Place

Let’s solve an example;

Find the gas pore volume when the initial gas FVF is 12, initial water saturation is 9 and initial gas in place is 13.

This implies that;

B_{gi} = Initial Gas FVF = 12

S_{wi} = Initial Water Saturation = 9

G = Initial Gas in Place = 13

(PV)_{g} = ^{GBgi} / _{1 – S}_{wi}

(PV)_{g} = ^{13 x 12} / _{1 – 9}

(PV)_{g} = ^{156} / _{-8}

(PV)_{g} = -19.5

Therefore, the **gas pore volume **is **-19.5**

**Calculating the Initial Gas FVF when the Gas Pore Volume, Initial Water Saturation and Initial Gas in Place is Given.**

B_{gi} = ^{(PV)g (1 – Swi)} / _{G}

Where;

B_{gi} = Initial Gas FVF

(PV)_{g} = Gas Pore Volume

S_{wi} = Initial Water Saturation

G = Initial Gas in Place

Let’s solve an example;

Find the initial gas FVF when the gas pore volume is 19, initial water saturation is 11 and initial gas in place is 16.

This implies that;

(PV)_{g} = Gas Pore Volume = 19

S_{wi} = Initial Water Saturation = 11

G = Initial Gas in Place = 16

B_{gi} = ^{(PV)g (1 – Swi)} / _{G}

B_{gi} = ^{19 (1 – 11)} / _{16}

B_{gi} = ^{19 (-10)} / _{16}

B_{gi} = ^{-190} / _{16}

B_{gi} = -11.875

Therefore, the **initial gas FVF **is **-11.875.**

**Calculating the Initial Water Saturation when the Gas Pore Volume, Initial Gas FVF and Initial Gas in Place is Given.**

S_{wi} = 1 – ^{GBgi} / _{(PV)}_{g}

Where;

S_{wi} = Initial Water Saturation

G = Initial Gas in Place

(PV)_{g} = Gas Pore Volume

B_{gi} = Initial Gas FVF

Let’s solve an example;

Find the initial water saturation when the initial gas FVF is 24, initial gas in place is 6 and gas pore volume is 46.

This implies that;

G = Initial Gas in Place = 6

(PV)_{g} = Gas Pore Volume = 46

B_{gi} = Initial Gas FVF = 24

S_{wi} = 1 – ^{GBgi} / _{(PV)}_{g}

S_{wi} = 1 – ^{6 x 24} / _{46}

S_{wi} = 1 – ^{144} / _{46}

S_{wi} = 1 – 3.13

S_{wi} = -2.13

Therefore, the **initial water saturation **is **-2.13.**