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Motivation

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Reservoir pressure dynamics away from wellbore and boundaries is representative of two very important complex reservoir properties: transmissibility 

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body\sigma
and pressure diffusivity 
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body\chi
.

These can be roughly estimated with a homogeneous reservoir model where wellbore and boundaries effects can be neglected.

Inputs & Outputs

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InputsOutputs

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bodyq_t

total sandface rate

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bodyp(t,r)

reservoir pressure

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body{p_i}

initial formation pressure



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body\sigma

transmissibility

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body\chi

pressure diffusivity

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Expand
titleDetailing


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body\sigma = \frac{k \, h}{\mu}

transmissibility

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body\mu

dynamic fluid viscosity

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

pressure diffusivity

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bodyc_t = c_r + c

total compressibility

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bodyk

absolute permeability

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body{c_r}

pore compressibility

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body{\phi}

porosity

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bodyc

fluid compressibility



Physical Model

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Mathematical Model

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\frac{\partial p}{\partial t} = \chi \, \left[  \frac{\partial^2 p}{\partial t^2} + \frac{1}{r} \frac{\partial p}{\partial r} \right]



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p(t=0,r) = p_i



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p(t, r=\infty) = p_i



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\left[ r \frac{\partial p}{\partial r} \right]_{r=0} = - \frac{q_t}{2 \pi \sigma}



Computational Model

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p(t,r) = p_i - \frac{q_t}{4 \pi \sigma} {\rm Ei} \left(-\frac{r^2}{4 \chi t} \right)



Approximations

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Late-time response


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p(t,r) = p_i - \frac{q_t}{4 \pi \sigma} \left[  
\gamma + \ln \left(\frac{r^2}{4 \chi t} \right) \right] 

= p_i - \frac{q_t}{4 \pi \sigma} \ln \left(\frac{2.24585 \, t}{r^2} \right)



See also

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Physics / Fluid Dynamics / Radial fluid flow / Line Source Solution

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