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Motivation

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In many practical cases the reservoir flow created by well is getting aligned with a  radial direction towards or away from well.

This type of flow is called radial fluid flow and a type library model provides a reference for radial fluid flow diagnostics.

Inputs & Outputs

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InputsOutputs

LaTeX Math Inline
bodyq_t

total sandface rate

LaTeX Math Inline
bodyp(t,r)

reservoir pressure

LaTeX Math Inline
body{p_i}

initial formation pressure

LaTeX Math Inline
body{p_{wf}(t)}

well bottomhole pressure

LaTeX Math Inline
bodyd

reservoir channel width



LaTeX Math Inline
body\sigma

transmissibility

LaTeX Math Inline
body\chi

pressure diffusivity

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Expand
titleDetailing


LaTeX Math Inline
body\sigma = \frac{k \, h}{\mu}

transmissibility

LaTeX Math Inline
body\mu

dynamic fluid viscosity

LaTeX Math Inline
body\chi = \frac{k}{\mu} \, \frac{1}{\phi \, c_t}

pressure diffusivity

LaTeX Math Inline
bodyc_t = c_r + c

total compressibility

LaTeX Math Inline
bodyk

absolute permeability

LaTeX Math Inline
body{c_r}

pore compressibility

LaTeX Math Inline
body{\phi}

porosity

LaTeX Math Inline
bodyc

fluid compressibility




Physical Model

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Constant rate production

LaTeX Math Inline
bodyq_t = \rm const

Radial fluid flow

LaTeX Math Inline
bodyp(t, {\bf r})

Slightly compressible fluid flow

LaTeX Math Inline
bodyc_t(p) = c_r +c = \rm const

Homogeneous reservoir

LaTeX Math Inline
bodyM({\bf r}, p)=M =\rm const

LaTeX Math Inline
body\phi({\bf r}, p)=\phi =\rm const

LaTeX Math Inline
bodyh({\bf r})=h =\rm const

Infinite boundary

LaTeX Math Inline
bodyr \rightarrow \infty


Mathematical Model

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Expand
titleDefinition



LaTeX Math Block
anchor52112
alignmentleft
\frac{\partial p}{\partial t}  = \chi \, \left( \frac{\partial^2 p}{\partial r^2} + \frac{1}{r} \frac{\partial p}{\partial r} \right)



LaTeX Math Block
anchor88AEG
alignmentleft
p(t = 0, {\bf r}) = p_i



LaTeX Math Block
anchor3MUX9
alignmentleft
p(t, r \rightarrow \infty ) = p_i



LaTeX Math Block
anchorEM415
alignmentleft
\frac{\partial p(t, r )}{\partial r} \bigg|_{r \rightarrow 0} = \frac{q_t}{\sigma \, d}



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Expand
titleSolution



LaTeX Math Block
anchorp_F
alignmentleft
p(t,r) = p_i + \frac{q_t}{4 \pi \sigma} \,  {\rm Ei} \bigg( - \frac{r^2}{4 \chi t} \bigg)



LaTeX Math Block
anchorpwf
alignmentleft
p_{wf}(t) = p_i + \frac{q_t}{4 \pi \sigma} \, \bigg[ - 2S +   {\rm Ei} \bigg( - \frac{r_w^2}{4 \chi t} \bigg) \bigg]





Expand
titleDerivation



Scope of Applicability

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Pressure TestingInfinite reservoir


Pressure Drop


LaTeX Math Block
anchor1EWTY
alignmentleft
\delta p = p_i - p_{wf}(t) \sim  \ln t + {\rm const}



Log derivative


LaTeX Math Block
anchorIBA4M
alignmentleft
t \frac{d (\delta p)}{dt}  \sim \rm const







Fig. 2. PTA Diagnostic plot for radial fluid flow


See also

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Physics / Fluid Dynamics / Radial fluid flow

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