The cement sheaf behind the casing of the petroleum well is subject to stress in production or injection conditions, created by the bottom-hole pressure across the perforated reservoir.

This can lead to cement break and creating a channel between the perforated reservoir and non-perforated reservoir.

Predictive model for Cement Failure @ model under pressure drop between perforated reservoir and non-perforated reservoir is given as:

(1)	$\begin{array}{l}\displaystyle \ \Delta P> \sigma_\mathrm{cem} \cdot \exp(- \left< \Delta P \right> \cdot t\, / \,\mu_\mathrm{cem})\end{array}$

(2)	$\begin{array}{l}\displaystyle \Delta P = \| \, BHP + \rho \, g \, (Z-Z_\mathrm{dat}) - P_\mathrm{non} \,\| \cdot \exp(- L \, / \, L_\mathrm{cem})\end{array}$

(3)	$\begin{array}{l}\displaystyle \left< \Delta P \right> \cdot t = \int_{0}^t \Delta P(t) \, dt\end{array}$

where

$\begin{array}{l}Z_\mathrm{dat}\end{array}$	Datum
$\begin{array}{l}BHP\end{array}$	BHP at datum $\begin{array}{l}Z_\mathrm{dat}\end{array}$
$\begin{array}{l}P_\mathrm{non}\end{array}$	Formation pressure in non-perforated reservoir
$\begin{array}{l}Z\end{array}$	True vertical depth between perforated and non-perforated reservoirs
$\begin{array}{l}L\end{array}$	Measured depth between perforated and non-perforated reservoirs (along well trajectory)
$\begin{array}{l}\rho\end{array}$	Average fluid density between datum and non-perforated reservoirs
$\begin{array}{l}L_\mathrm{cem}\end{array}$	Cement stress attenuation characteristic length, typical = 3 – 10 m
$\begin{array}{l}\mu_\mathrm{cem}\end{array}$	Cement apparent viscosity , typical $\begin{array}{l}\mu_\mathrm{cem} \sim10^{10} \; \mathrm{MPa} \cdot \mathrm{s}\end{array}$
$\begin{array}{l}\sigma_\mathrm{cem}\end{array}$	Cement tensile strength, typical 0.5 – 3 MPa
$\begin{array}{l}g\end{array}$	Standard gravity constant, $\begin{array}{l}g = 9.80665 \, \mathrm{m}/\mathrm{s}^2\end{array}$

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