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Motivation

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In many practical cases the reservoir flow created by well or group of wells is getting aligned with a specific linear direction away from well.

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

Inputs & Outputs

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InputsOutputs

LaTeX Math Inline
bodyq_t

total sandface rate

LaTeX Math Inline
bodyp(t,x)

reservoir pressure

LaTeX Math Inline
bodyp_i

initial formation pressure

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

pressure diffusivity

LaTeX Math Inline
bodyk

absolute permeability

LaTeX Math Inline
body\phi

porosity

LaTeX Math Inline
body\mu

dynamic fluid viscosity

LaTeX Math Inline
bodyc_t = c_r + c

total compressibility

LaTeX Math Inline
bodyc_r

pore compressibility

LaTeX Math Inline
bodyc

fluid compressibility




Physical Model

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Constant rate production

LaTeX Math Inline
bodyq_t = \rm const

Linear fluid flow

LaTeX Math Inline
bodyp(t, x)

Slightly compressible fluid flow

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

Homogeneous reservoir

LaTeX Math Inline
bodyM(x, p)=M =\rm const

LaTeX Math Inline
body\phi(x, p)=\phi =\rm const

LaTeX Math Inline
bodyh(x)=h =\rm const

Infinite boundary

LaTeX Math Inline
bodyx \rightarrow \infty


Mathematical Model

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Expand
titleDefinition



LaTeX Math Block
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\frac{\partial p}{\partial t}  = \chi \, \frac{d^2 p}{dx^2}



LaTeX Math Block
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p(t = 0, x) = p_i



LaTeX Math Block
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p(t, x \rightarrow \infty ) = p_i



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



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Expand
titleSolution



LaTeX Math Block
anchorLB89P
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p(t,x) = p_i - \frac{q_t}{\sigma \, d} \bigg[ \sqrt{\frac{4 \chi t}{\pi}} \exp \bigg( -\frac{x^2}{4 \chi t} \bigg) - x \, \bigg[ 1- {\rm erf} \bigg(\frac{x}{\sqrt{4 \, \chi \, t}} \bigg) \bigg]  \bigg]



LaTeX Math Block
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p_{wf}(t) = p(t,x=0)= p_i - \frac{q_t}{\sigma \, d} \,  \sqrt{\frac{4 \chi t}{\pi}} 





Expand
titleDerivation



Scope of Applicability

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Pressure TestingChannel or Narrow reservoir compartment


Pressure Drop


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\delta p = p_i - p_{wf}(t) \sim t^{1/2}





Log derivative


LaTeX Math Block
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t \frac{d (\delta p)}{dt}  \sim t^{1/2}














Fig. 2.PTA Diagnostic plot for linear fluid flow in reservoir channel


Pressure TestingInfinite conductivity fracture


Pressure Drop


LaTeX Math Block
anchor1EWTY
alignmentleft
\delta p = p_i - p_{wf}(t) \sim t^{1/2}





Log derivative


LaTeX Math Block
anchorIBA4M
alignmentleft
t \frac{d (\delta p)}{dt}  \sim t^{1/2}














Fig. 2. PTA Diagnostic plot for linear fluid flow in infinite conductivity fracture




See also

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Physics / Fluid Dynamics / Linear fluid flow

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