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Gas in Place

Gas in place, abbreviated as \(GIP\), also called original gas in place or gas initially in place, is the total volume of natural gas estimated to exist in a subsurface reservoir at its initial conditions before the start of any production or extraction activities.  This quantity represents the entire resource base of the gas accumulation in the reservoir rock, quantified at standard surface conditions (typically 60°F and 14.7 psia) to allow direct comparison with produced volumes, after accounting for the expansion of gas from reservoir pressure and temperature to surface conditions via the gas formation volume factor.  It includes free gas occupying the pore space (adjusted for water saturation) and may incorporate associated solution gas in certain reservoir types, though in dry-gas systems it primarily reflects the free-gas component. 

Gas in Place Formula 

  • 43,560 = conversion factor from acre-ft to \(ft^3\)

\( OGIP \;=\;  \dfrac{43560 \; A \cdot h \cdot n \cdot (1 - W_s )}{B_g }\)     (Gas in Place)

\( A \;=\;  \dfrac{ OGIP \cdot B_g }{ 43560 \; h \cdot n \cdot (1 - W_s )}   \)

\( h \;=\; \dfrac{ OGIP cdot B_g }{ 43560 \; A \cdot n \cdot (1 - W_s )}   \)

\( n \;=\;  \dfrac{ OGIP \cdot B_g }{ 43560 \; A \cdot h \cdot (1 - W_s )}   \)

\( W_s \;=\;  1 -  \dfrac{ OGIP \cdot B_g }{ 43560 \; A \cdot h \cdot n }   \)

\( B_g \;=\;  \dfrac{43560 \; A \cdot h \cdot n \; (1 - W_s )  }{ OGIP }    \)
Symbol English Metric
\( GIP \) = Gas in Place \(bbl\) -
\( A \) = Reservoir Area, acres from map data \(acre\) -
\( h \) = Reservoir Thickness \(ft\) -
\( n \) = Porosity \(dimensionless\) -
\( W_s \) = Water Saturation \(dimensionless\) -
\( B_g \) = Gas Formation Volume Factor (cubic feet of gas at standard conditions per cubic foot of gas at reservoir conditions) \(bbl\;/\;ft^3\) -

This parameter forms the foundation for all subsequent reservoir evaluations, including the calculation of recoverable reserves through application of a recovery factor, economic assessments, and field development planning.  Established methods for its determination rely on static volumetric approaches using geological and petrophysical data or dynamic techniques such as material balance analysis from pressure and production history.

Key Points about Gas in Place
Original Gas in Place (OGIP)  -  This is the total amount of gas present in the reservoir before any production starts.
Remaining Gas in Place (RGIP)  -  This refers to the amount of gas left in the reservoir after some production has occurred.
Recoverable vs. Non-Recoverable Gas  -  Not all gas in place can be extracted.  The recoverable portion depends on factors like reservoir pressure, permeability, and extraction technology, typically expressed as a recovery factor (60-80% in conventional reservoirs).

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Gas in Place formulas

\( OGIP \;=\;  A \cdot  h \cdot n \cdot S_g \cdot \frac{ 1 }{ B_g }  \)     (Gas in Place)

\( A \;=\;  \dfrac{ OGIP \cdot B_g  }{ h \cdot n \cdot S_g  }\)

\( h \;=\;  \dfrac{ OGIP \cdot B_g  }{ A \cdot n \cdot S_g  }\)

\( n \;=\;  \dfrac{ OGIP \cdot B_g  }{ A \cdot h \cdot S_g  }\)

\( S_g \;=\;  \dfrac{ OGIP \cdot B_g  }{ A \cdot h \cdot n  }\)

\( B_g \;=\;  \dfrac{ A \cdot  h \cdot n \cdot S_g  }{  OGIP }  \)
Symbol English Metric
\( OGIP \) = Gas in Place \(bbl\) -
\( A \) = Reservoir Area, acres from map data \( acre \) -
\( h \) = Reservoir Thickness \( ft \) -
\( n \) = Porosity \(dimensionless\) -
\( G_s \) = Gas Saturation \(dimensionless\) -
\( B_g \) = Gas Formation Volume Factor (cubic feet of gas at standard conditions per cubic foot of gas at reservoir conditions) \(bbl\;/\;ft^3\) -