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It splits into two components:
Open porosity | Closed porosity | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| with interconnected pores | with isolated pores |
subject to condition:
| LaTeX Math Block | ||||
|---|---|---|---|---|
| ||||
\phi_e = \phi_{\rm opn} + \phi_{\rm cls} |
Effective porosity is a function of reservoir pressure at a given location
| LaTeX Math Inline | ||
|---|---|---|
|
| LaTeX Math Block | ||||
|---|---|---|---|---|
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\phi_e(\mathbf{r}, \ p) = \phi_0{ei}(\mathbf{r}) \exp \left[ - \int_{p_i}^p c_r\phi(p) \, dp \right] |
where
| pore compressibility (see also Pore compressibility @model ) | ||||||||
| effective porosity at the initial formation pressure | ||||||||
| initial formation pressure |
This leads to the effect of Porosity Shrinkage.
Since the pore compressibility is very low (~ cϕ = 0.5 ÷ 1.5 GPa-1) and has a weak dependence on reservoir pressure for subsurface rocks in petroleum reservoirs the
can be written as:LaTeX Math Block Reference anchor pher
| LaTeX Math Block | ||||
|---|---|---|---|---|
| ||||
\phi_e(\mathbf{r}, \ p) = \phi_{ei}(\mathbf{r}) \cdot \left[ 1 + c_\phi \, (p-p_i) + 0.5 \, c_\phi^2 \, (p-p_i)^2 \right] |
Most Subsurface E&P Disciplines (except Petrophysics) usually omit index "e" and denote Effective porosity as
.LaTeX Math Inline body \phi = \phi_e
See also
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Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics (PP) / Volumetric Rock Model
[ Basic reservoir properties ] [ Pore volume ] [ Connected pore volume ] [ Closed pore volume ] [ Porosity ] [ Open porosity ] [ Closed porosity ][ Initial Porosity ϕi ]
[ Pore compressibility @model ]
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