# Remaining gas in place in coalbed methane reservoirs

## Input(s)

A: Drainage Area (acres)

Ø: Porosity (fraction)

$$\mathrm{h}$$: Thickness (ft)

$$\mathrm{B}_{\mathrm{w}}$$: Water Formation Volume Factor (bbl/STB)

$$\mathrm{W}_{\mathrm{p}}$$: Cumulative Water Produced (bbl)

$$\mathrm{S}_{\mathrm{wi}}$$: Water Saturation (fraction)

$$\mathrm{P}_{\mathrm{i}}$$: Initial Pressure $$(\mathrm{psi})$$

P: Current Reservoir Pressure (psi)

$$\mathrm{c}_{\mathrm{f}}$$: Formation Compressibility $$(1 / \mathrm{psi})$$

$$\mathrm{c}_{\mathrm{w}}$$: Water Compressibility (1/psi)

$$\mathrm{E}_{\mathrm{g}}$$: Gas Expansion Factor $$(\mathrm{SCF} / \mathrm{bbl})$$

## Output(s)

$$\mathrm{G}_{\mathrm{R}}$$: Remaining Gas at Reservoir Pressure (SCF)

## Formula(s)

$\mathrm{G}_{\mathrm{R}}=7758 * \mathrm{~A} * \mathrm{~h} * \emptyset * \mathrm{E}_{\mathrm{g}} *\left(\frac{\left(\frac{\mathrm{B}_{\mathrm{w}} * \mathrm{~W}_{\mathrm{p}}}{7758 * \mathrm{~A} * \mathrm{~h} * \emptyset}\right)+\left(1-\mathrm{S}_{\mathrm{wi}}\right)-\left(\mathrm{P}_{\mathrm{i}}-\mathrm{P}\right) *\left(\mathrm{c}_{\mathrm{f}}+\mathrm{c}_{\mathrm{w}} * \mathrm{~S}_{\mathrm{wi}}\right)}{1-\left(\mathrm{P}_{\mathrm{i}}-\mathrm{P}\right) * \mathrm{c}_{\mathrm{f}}}\right)$

## Reference(s)

Ahmed, T., McKinney, P.D. 2005. Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter: 3, Page: 227.

## Related

### Diffusion through cleat spacing in coalbed methane reservoirs

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