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Fluid flow with fluid pressure gradient  

LaTeX Math Inline
body\nabla p(t, {\bf r})
 and velocity  LaTeX Math Inlinebody
 linearly changing in time:

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alignmentleft
p(t, {\bf

...

 r}) = \psi({\bf r})

...

 + A \cdot t, \quad A = \rm const


The fluid temperature  

LaTeX Math Inline
bodyT(t, {\bf r})
 is supposed to vary slowly enough to provide quasistatic equilibrium.


The fluid velocity 

LaTeX Math Inline
body{\bf u}(t, {\bf r})
 may not be stationary.

In the most general case (both reservoir and pipelines) the fluid motion equation is of fluid pressure and pressure gradient:

LaTeX Math Block
LaTeX Math Block
alignmentleft
\nabla p(t, {\bf r}) = \nabla p({\bf r})
LaTeX Math Block
anchoru
alignmentleft
{\bf u}(t, {\bf r}) = F({\bf u}({\bf r})r}, p, \nabla p) 

with right side dependent on time through the pressure variation.


In case of the flow with velocity dependent on pressure  gradient only The fluid temperature  

LaTeX Math Inline
bodyT(t, {\bf u} = {\bf u}({\bf r}, \nabla p)
) the PSS flow velocity will be stationary as the right side of  is supposed to vary slowly enough to provide quasistatic equilibrium.
LaTeX Math Block Reference
anchoru
 is not dependant on time.


In terms of Well Flow Performance the PSS flow meansWell flow regime with constant rate and constant delta pressure between wellbore and formation does not change in time:

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anchor1
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q_t(t) = \rm const

...

During the PSS regime the formation pressure declines  also declines linearly with time: 

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bodyp_e(t) \sim t
.

...

Fig. 1. PTA Diagnostic Plot for vertical well in single-layer homogeneous reservoir with impermeable circle boundary (PSS).

Pressure is in blue and log-derivative is in red.


See Also

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Petroleum Industry / Upstream /  Production / Subsurface Production / Field Study & Modelling / Production Analysis / PSS Diagnostics

Steady State (SS) well fluid flow regime ]