One of the measures of rock quality in terms of availability for flow:
{ \rm FZI } = \frac{\rm RQI}{\phi_z} |
where
\rm RQI | Rock Quality Index |
\phi_z | normalised porosity |
Unit = μm
It has much weaker dependence on effective porosity and shaliness and can be often considered constant within a given lithofacies which makes it a very efficient tool for lithofacies analysis
The constant FZI means that permeability strictly follows Cozeny-Karman permeability @model, although it's rarely met in practise.
The FZI depends on grains size distribution, shape and packing and can be modelled as follows:
(1) | {\rm FZI} = \frac{1}{\sqrt{F_S} \, S_{gV} \, \tau } |
where
S_{gV} = \Sigma_e/V_\phi | \Sigma_e | pore surface area | |
F_S | pore shape factor | V_\phi | pore volume |
\tau | pore channel tortuosity |
In some practical cases this can be further simplified to:
(2) | {\rm FZI} \approx 0.0037 \cdot \frac{d}{\tau } |
where
d | average grain size |
One of the proposed qualification of reservoir quality based on FZI is given by the Table 1.
Table1. One of the qualification schedules of reservoir quality.
FZI Value | Reservoir Quality |
---|---|
FZI > 8.0 | Very Good |
3.5 < FZI ≤ 8.0 | Good |
1.0 < FZI ≤ 3.5 | Medium |
0.45 < FZI ≤ 1.0 | Poor |
FZI ≤ 0.45 | Very Poor |
See also
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics
[ Rock Quality Index (RQI) ] [ Absolute permeability @model ]