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Motivation

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Excerpt Include
Aquifer Drive
Aquifer Drive
nopaneltrue


Inputs & Outputs

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InputsOutputs

LaTeX Math Inline
bodyp(t)

field-average formation pressure at time moment

LaTeX Math Inline
bodyt

LaTeX Math Inline
body

Q^{\downarrow}_{AQ}

--uriencoded--Q%5e%7B\downarrow%7D_%7BAQ%7D(t)

Cumulative
cumulative subsurface water influx from aquifer

LaTeX Math Inline
bodyp_i

initial formation pressure

LaTeX Math Inline
body

q^{\downarrow}_{AQ}

--uriencoded--q%5e%7B\downarrow%7D_%7BAQ%7D(t) = \

frac{dQ^{\downarrow}_{AQ}}{dt}Subsurface water flowrate from aquifer LaTeX Math Inlinebody

frac%7BdQ%5e%7B\downarrow%7D_%7BAQ%7D%7D%7Bdt%7D

subsurface water flowrate from aquifer

LaTeX Math Inline
body--uriencoded--J_%7BAQ%7D

aquifer Productivity Index

LaTeX Math Inline
body--uriencoded--\displaystyle \tau = \frac%7Bc_t \, V_\phi%7D%7BJ_%7BAQ%7D%7D

aquifer relaxation time



Expand
titleDetailing
Detailing Inputs

LaTeX Math Inline
body\displaystyle J_{AQ} = \frac{\theta}{2\pi} \cdot \frac{2 \pi \sigma}{\ln \frac{A_{AQ}}{A_e}+0.75}


aquifer Productivity Index

LaTeX Math Inline
body\theta

central angle of net pay areaaquifer contact

LaTeX Math Inline
body\sigma

aquifer transmissibility

LaTeX Math Inline
bodyA_e

net pay area

LaTeX Math Inline
bodyA_{AQ}

aquifer area

LaTeX Math Inline
body\displaystyle \tau = \frac{V_{AQ} \, c_t}{J_{AQ}}

aquifer relaxation time

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LaTeX Math Inline
body

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c_t=c_r +c_w

aquifer

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total compressibility

LaTeX Math Inline
body

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c_

...

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pore compressibility 

LaTeX Math Inline
body

...

c_

...

...

water compressibility

LaTeX Math Inline
bodyV_{AQ} = A_e

...

Assumptions

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\cdot h \cdot \phi

aquifer volume 

LaTeX Math Inline
bodyh

aquifer effective thickness

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LaTeX Math Inline
body\phi

aquifer porosity


Physical Model

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Radial Composite Reservoir

Image Added

Const Productivity IndexAquifer
LaTeX Math Block
alignmentleft
J_{AQ} = \frac{q_{AQ}}{
A_e cross-sectional area in  LaTeX Math Inlinebody
p_{AQ}(t)
=p_i =
-p(t)} = \rm const
Aquifer pressure is constant LaTeX Math Inlinebody
Pseudo Steady State Flow
LaTeX Math Block
alignmentleft
p
J
_{AQ}(t) =
\rm constAquifer Productivity Index is constant

...

 p_i - \frac{Q_{AQ}(t)}{V_{AQ} \cdot c_t}





Fig. 1. Fetkovich aquifer drive schematic



Mathematical Model

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LaTeX Math Block
anchor
1
Fetkovich_PSS
alignmentleft
\tau \cdot \frac{d 
Q
Q^{\downarrow}_{AQ}}{dt} +  
\frac
Q^{
1}{
\
tau
downarrow}
Q
_{AQ} = 
J
с_t \, V_\phi \cdot \left[ 
(
 p_i - p(t)
)
 \right]
LaTeX Math Block
anchor1
alignmentleft
J
q^{\downarrow}_{AQ}
(t)=
\frac{
2
d 
\pi \sigma}{\ln \frac{A
Q^{\downarrow}_{AQ}}{
A_e} - \frac{3}{4} }
dt} 

 which can be explicitly integrated:

LaTeX Math Block
anchor
1
Fetkovich_PSS
alignmentleft
q
Q^{\downarrow}_{AQ}
=\frac{d Q
(t) = J_{AQ} \, \exp \left( -\frac{t}{
dt}

where

...

LaTeX Math Inline
bodyQ_{AQ}(t)

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water influx from aquifer at time moment

LaTeX Math Inline
bodyt

...

LaTeX Math Inline
body\sigma

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LaTeX Math Inline
bodyJ = \rm const

...

...

LaTeX Math Inline
body\displaystyle \tau = \frac{V_{AQ} \, c_t}{J}

...

LaTeX Math Inline
bodyp_i

...

LaTeX Math Inline
bodyA_{AQ}

...

LaTeX Math Inline
bodyp(t)

...

field-average formation pressure at time moment

LaTeX Math Inline
bodyt

...

LaTeX Math Inline
bodyA_e

...

\tau} \right) \, \int_0^t   \big[ p_i - p(\xi) \big] \, \exp \left( \frac{\xi}{\tau} \right) \, d \xi



Expand
titleDerivation
Panel
bgColorCORNSILK

Assumption #1 = Const Productivity Index Aquifer

Expand
titleDerivation
Const PI expansion

:

LaTeX Math Block
alignmentleft
q_{AQ} = \frac{d Q_{
WAQ
AQ}}{dt} = J_{AQ} \cdot ( p_{AQ}(t) - p(t))
Finite-volume reservoir PSS depletion


Assumption #2 = Pseudo Steady State Flow:

LaTeX Math Block
alignmentleft
p_{AQ}(t) = p_i - \frac{Q_{
WAQ
AQ}}{c_t \, V_
{WAQ} c_t}
\phi}


Eliminating

LaTeX Math Inline
bodyp_{AQ}(t)
one arrives to
LaTeX Math Block Reference
anchorFetkovich_PSS
.


See Also

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Petroleum Industry / Upstream / Subsurface E&P Disciplines / Field Study & Modelling / Aquifer Drive / Aquifer Drive @modelModels

Reference

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 1.   Fetkovich, M.J. 1971. A Simplified Approach to Water Influx Calculations—Finite Aquifer Systems. J Pet Technol 23 (7): 814–28. SPE-2603-PAhttp://dx.doi.org/10.2118/2603-PA