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Compressibility Drive in Gas Reservoirs

on . Posted in Reservoir Engineering

In gas reservoirs, compressibility drive is the natural energy mechanism by which gas expands as the pressure within the reservoir declines, helping to push gas toward the production wells.  This is primarily due to the high compressibility of gases compared to liquids.  Compressibility is how much a substance changes in volume when subjected to pressure changes.

The compressibility drive is the dominant mechanism in dry gas reservoirs, where water or other fluid influx is minimal.  The reservoir's performance is strongly dependent on the ability of gas to expand, making it a crucial factor for understanding reservoir depletion, production forecasting, and recovery strategies. 

Key Aspects of Compressibility Drive

Expansion of Gas  -  As gas is produced and pressure decreases, the remaining gas expands.  This expansion helps drive the remaining gas toward production wells.
Pore Space Utilization  -  In a gas reservoir, the gas is stored in the pore spaces of rocks.  As pressure decreases, the gas expands to fill more of these spaces, displacing other fluids and continuing to move toward the surface.
Reservoir Energy  -  In a gas reservoir, the energy for production is mainly derived from the gas compressibility, as gas can expand significantly in response to pressure declines.  There is no significant contribution from water influx, unlike in oil reservoirs that might have a water drive.
Declining Pressure  -  Over time, as gas is produced, reservoir pressure decreases, and with it, the drive energy weakens.  Gas reservoirs typically exhibit a steep decline in production rates due to this pressure drop.

 

 Compressibility Drive in Gas Reservoirs formula

\( CI \;=\; G \;  G_{zd}  \;/\; G_{fv} \; G_p  \)     (Compressibility Drive in Gas Reservoirs)

\( G \;=\; CI \; G_{fv} \; G_p  \;/\; G_{zd}  \)

\( G_{zd} \;=\; CI \; G_{fv} \; G_p  \;/\; G  \)

\( G_{fv} \;=\; G \;  G_{zd}  \;/\; CI \; G_p  \)

\( G_p \;=\; G \;  G_{zd}  \;/\; CI \; G_{fv}  \)
Symbol English Metric
\( CI \) = Compressibility Index \(dimensionless\) -
\( G \) = Gas in Place \(MSCF\) -
\( G_{zd} \) = Gas Compressibility Drive \(ft^3\;/\;MSCF\) -
\( G_{fv} \) = Gas Formation Volume Factor \(ft^3\;/\;MSCF\) -
\( G_p \) = Gas Produced \(MSCF\) -

 

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Tags: Petroleum Reservoir

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