Time interval of pressure transition when pressure variation drop 

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\Deltadelta p = p_{wf}(0) - p_{wf}(t) =\sim p_{wf}(0) - p_i - \frac{q_t}{4 \pi \sigma} \, \bigg[ - 2S +  \gamma 

- \ln \bigg(  \frac{4 \chi t}{r_w^2} \bigg) \bigg]

and hence the pressure pressure log-derivative stays  stays constant:

\Deltadelta p ' = \frac{d \, \Delta p}{d \, \ln t}  =  \frac{q_t}{4 \pi \sigma} = \rm const

Since IARF is normally used to define a flow regime during a certain finite period of time, the term "infinite acting" is a misnomer.

This  pressure diffusion regime is native to radial fluid flow in This flow regime is native to pressure diffusion in vertical well, homogeneous reservoir and no boundary (see Fig. 1).

The other popular occurrence of IARF is before PSS (Fig. 2) and SS (Fig. 3).

Image Removed developed between and

Image Added	Image AddedImage Removed	Image Added
Fig. 1. PTA Diagnostic Plot with IARF regime developed developing after 100 hrs	Fig. 2. PTA Diagnostic Plot with IARF regime developing after 100 hrs until PSS at 1,000 hrs	Fig. 3. PTA Diagnostic Plot with IARF regime	developing after 100 hrs	until SS at 1,000 hrs

See Also

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Petroleum Industry / Upstream / Subsurface E&P Disciplines /  Field Study & Modelling / Reservoir Flow Simulation 

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