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Motivation

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Excerpt Include
Aquifer Drive
Aquifer Drive
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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
bodyQ^{\downarrow}_{AQ}(t)

Cumulative subsurface water influx from aquifer

LaTeX Math Inline
bodyp_i

initial formation pressure

LaTeX Math Inline
bodyq^{\downarrow}_{AQ}(t) = \frac{dQ^{\downarrow}_{AQ}}{dt}

Subsurface water flowrate from aquifer

LaTeX Math Inline
bodyB

water influx constant





LaTeX Math Inline
body\chi

aquifer diffusivity

LaTeX Math Inline
bodyA_e

net pay area

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Expand
titleDetailing


Detailing Inputs

LaTeX Math Inline
bodyB = \frac{\theta}{2\pi} \cdot A_e \cdot h_a \cdot \phi_a \cdot c_t

water influx constant

LaTeX Math Inline
body\theta

central angle of net pay area ↔ aquifer contact

LaTeX Math Inline
bodyh_a

aquifer effective thickness

LaTeX Math Inline
body\phi_a

aquifer porosity

LaTeX Math Inline
bodyc_t=c_r +c_w

aquifer total compressibility

LaTeX Math Inline
bodyc_r

aquifer pore compressibility 

LaTeX Math Inline
bodyc_w

aquifer water compressibility



Assumptions

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Transient flow in Radial Composite Reservoir



Equations

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LaTeX Math Block
anchor1
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\frac{d Q^{\downarrow}_{AQ}}{dt} = q^{\downarrow}_{AQ}(t)



LaTeX Math Block
anchor1
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q^{\downarrow}_{AQ}(t)= C_a \cdot \frac{\partial p_a(t,r)}{\partial r} \bigg|_{r=r_e}



LaTeX Math Block
anchorVEHP
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p_a(t, r)= p(0) + \int_0^t p_1 \left(\frac{(t-\tau) \cdot \chi}{r_e^2}, \frac{r}{r_e} \right) \dot p(\tau) d\tau




LaTeX Math Block
anchorRC
alignmentleft
\frac{\partial p_1}{\partial t_D} =  \frac{\partial^2 p_1}{\partial r_D^2} + \frac{1}{r_D}\cdot \frac{\partial p_1}{\partial r_D}



LaTeX Math Block
anchorCT
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p_1(t = 0, r_D)= 0



LaTeX Math Block
anchorCT
alignmentleft
p_1(t, r_D=1) = 1




LaTeX Math Block
anchor1
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\frac{\partial p_1}{\partial r_D} \bigg|_ {r_D=r_a/r_e} = 0


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Expand
titleDerivation

Transient flow in Radial Composite Reservoir:


LaTeX Math Block
anchorRC
alignmentleft
\frac{\partial p_a}{\partial t} = \chi \cdot \left[ \frac{\partial^2 p_a}{\partial r^2} + \frac{1}{r}\cdot \frac{\partial p_a}{\partial r} \right]



LaTeX Math Block
anchor1
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p_a(t = 0, r)= p(0)



LaTeX Math Block
anchor1
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p_a(t, r=r_e) = p(t)



LaTeX Math Block
anchorp1_PSS
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\frac{\partial p_a}{\partial r} \bigg|_ {r=r_a} = 0


One can easily check that pressure from

LaTeX Math Block Reference
anchorVEHP
honors the whole set of equations
LaTeX Math Block Reference
anchorRC
LaTeX Math Block Reference
anchorp1_PSS
and as such defines a unique solution of the above problem.


See Also

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


Reference

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 1. van Everdingen, A.F. and Hurst, W. 1949. The Application of the Laplace Transformation to Flow Problems in Reservoirs. Trans., AIME 186, 305.

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