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The general form of non-linear 
single-phase pressure diffusion @model with the finite number of sources/sinks  wells is given by: 

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anchorPZ
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\phi \cdot c_t \cdot \partial_t p + \nabla  {\bf u}  
+ c \cdot ( {\bf u} \, \nabla p)
= \sum_k q_k(t) \cdot \delta({\bf r}-{\bf r}_k)
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anchoruu
alignmentleft
{\bf u} = - M \cdot ( \nabla p - \rho \, {\bf g})
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anchorqGamma
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{\intrm F}_{\Gamma} \(p, {\bf u} \,  d {\bf \Sigma} = q_\Gamma(t)) = 0

where

LaTeX Math Inline
body--uriencoded--p(t, %7B\bf r%7D)

reservoir pressure

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bodyt

time

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body--uriencoded--\rho(%7B\bf r%7D,p)

fluid density 

LaTeX Math Inline
body--uriencoded--%7B\bf r %7D

position vector

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body--uriencoded--\phi(%7B\bf r%7D, p)

effective porosity 

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body--uriencoded--%7B\bf r %7D_k

position vector of the

LaTeX Math Inline
bodyk
-th source

LaTeX Math Inline
body--uriencoded--c_t(%7B\bf r%7D,p)

total compressibility 

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body\delta ( \bf r )

Dirac delta function

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bodyM = k / \mu

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body\nabla

gradient operator

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bodyk

formation permeability to a given fluid

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body--uriencoded--%7B \bf g %7D

gravity vector

LaTeX Math Inline
body\mu

dynamic viscosity of a given  fluid

LaTeX Math Inline
body--uriencoded--%7B \bf u %7D

fluid velocity under Darcy flow 

LaTeX Math Inline
bodyq_k(t)

sandface flowrates of the

LaTeX Math Inline
bodyk
-th

source

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body\Gamma

reservoir boundary

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body

q_\Gamma(t)

--uriencoded--%7B\rm F%7D_%7B\Gamma%7D(p, %7B\bf u%7D)

flow through

the reservoir boundary

LaTeX Math Inline
body\Gamma
, which

is 

is usually the aquifer or gas cap



Expand
titleDerivation
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Derivation of Single-phase pressure diffusion @model



The alternative form is to write down equations 

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anchorPZ
 and 
LaTeX Math Block Reference
anchoruu
 in reservoir volume outside wellbore and match the solution to the fluid flux through the well-reservoir contact:

LaTeX Math Block
anchorPZ1
alignmentleft
\phi \cdot c_t \cdot \partial_t p + \nabla  {\bf u}  
+ c \cdot ( {\bf u} \, \nabla p)
= 0
LaTeX Math Block
anchoruu1
alignmentleft
{\bf u} = - M \cdot ( \nabla p - \rho \, {\bf g})
LaTeX Math Block
anchorqk
alignmentleft
\int_{\Sigma_k} \, {\bf u} \,  d {\bf \Sigma} = q_k(t)
LaTeX Math Block
anchorqGamma
alignmentleft
{\
int
rm F}_{\Gamma}
\
(p, {\bf u}
\, d {\bf \Sigma} = q_\Gamma(t)
) = 0

where

q_\Gamma(t

LaTeX Math Inline
body\Sigma_k

well-reservoir contact of the 

LaTeX Math Inline
bodyk
-th well

LaTeX Math Inline
body

\Gamma

LaTeX Math Inline
body--uriencoded--d %7B\bf \Sigma%7D

normal vector of differential area on the well-reservoir contact, pointing inside wellbore

LaTeX Math Inline
bodyq_k(t)

sandface flowrates at the 

LaTeX Math Inline
bodyk
-th well (could be injecting to or producing from the reservoir )

LaTeX Math Inline
body

)flow through the reservoir boundary

LaTeX Math Inline
body\Gamma
, which is aquifer or gas cap


Physical models of pressure diffusion can be split into two categories: Newtonian and Rheological (non-Newtonian) based on the fluid stress model.

...


The simplest analytical solutions for pressure diffusion are given by 1DL Linear-Drive Solution (LDS) and 1DR Line Source Solution (LSS)The table below shows a list of popular well and reservoir pressure diffusion models.

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Fractured vertical well

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Multifrac horizontal well

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See also

...

Physics / Mechanics / Continuum mechanics / Fluid Mechanics / Fluid Dynamics / Pressure Diffusion / Pressure Diffusion @model

[ Aquifer Drive Models ] [ Gas Cap Drive Models ]

[ Linear single-phase pressure diffusion @model ]