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| for producer |
| for injector |
| LaTeX Math Inline |
|---|
| body | q=q_{\rm liq}=q_o+q_w |
|---|
|
| for oil producer |
| for gas producer or injector |
| for water injector or water-supply producer |
For a single-layer formation with low-compressibility fluid the PI does not depend on flowrate
and WFP – Well Flow Performance plot is reperented by a straight line (Fig. 1)
This is a typical WFP – Well Flow Performance plot for water supply wells, water injectors and oil producers above bubble point.
The PI can be estimated using the Darcy equation:
| LaTeX Math Block |
|---|
|
J_s = \frac{2 \pi \sigma}{ \ln \frac{r_e}{r_w} + \epsilon+ S} |
For gas wells, condensate producers, light-oil producers, and oil producers below bubble point
the fluid compressibility is high, formation flow in well vicinity becomes non-linear (deviating from Darcy) and free gas slippage effects inflict the downward trend on WFP – Well Flow Performance plot (Fig. 2).It can be interpreted as deterioration of near-reservoir zone permeability with fluid velocity growth.
The alternative way to define the
vs
correlation is to present
as a function of
:
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| Note |
|---|
|
Despite of terminological similarity there is a big difference in the way WFP and Well Testing deal with formation pressure and flowrates which results in a big difference in productivity index definition and corresponding analysis. This difference is summarized in the table below:
| WFP | Well Testing |
|---|
| Formation pressure | – field-average pressure within the drainage area
| – pressure value at boudary of the drainage area
| | Flow rate | | | LaTeX Math Inline |
|---|
| body | q_t = B_w \, q_W + \frac{B_o - R_s B_g}{1 - R_v R_s} \, q_O + \frac{B_g - R_v B_o}{1 - R_v R_s} \, q_G |
|---|
|
– total flowrate at sandface |
|
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This is a typical WFP – Well Flow Performance plot for water supply wells, water injectors and oil producers above bubble point.
For gas wells, condensate producers, light-oil producers, and oil producers below bubble point
the fluid compressibility is high, formation flow in well vicinity becomes non-linear (deviating from Darcy) and free gas slippage effects inflict the downward trend on WFP – Well Flow Performance plot (Fig. 2).It can be interpreted as deterioration of near-reservoir zone permeability with fluid velocity growth.
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VLP – Vertical Lift Performance
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