Specific electrical resistivity or specific electrical conductivity of formations is defined by mineralization of the rock matrix and saturating fluids which are in due turn depend on formation water-saturated shaliness , formation porosity and water saturation volumetric share .
Specific electrical resistivity is defined:
\frac{1}{R_t} = \frac{\phi_e^m \, s_w^n }{A R_w} \quad \Rightarrow \quad s_w = \Big ( \frac{A}{\phi_e^m} \; \frac{R_w}{R_t} \Big) ^{1/n} |
where
specific electrical resistivity of formation water | ||
dimensionless constant, characterizing the rock matrix contribution to the total electrical resistivity | 0.5 ÷ 1, default value is 1 for sandstones and 0.9 for limestones | |
formation matrix cementation exponent | 1.5 ÷ 2.5, default value is 2 | |
formation matrix water-saturation exponent | 1.5 ÷ 2.5, default value is 2 |
Archie model is usually used in:
Indonesia model is the same Archie model:
\frac{1}{R_t} = \frac{\phi_e^m \, s_w^n }{A R_w} \quad \Rightarrow \quad s_w = \Big ( \frac{A}{\phi_e^m} \; \frac{R_w}{R_t} \Big) ^{1/n} |
where constant is defined by formation shaliness :
\frac{1}{A} = 1 + \Big( \frac{V_{sh}^{2-V_{sh}}}{\phi_e} \, \frac{R_w}{R_{sh}} \Big)^{1/2} |
where
specific electrical resisitvity fo shale |
Simandeux model suggest a more complicated correlation between resitvity and water saturation :
\frac{1}{R_t} = \frac{\phi_e^m \, s_w^n}{A R_w (1-V_{sh})} + \frac{V_{sh}}{R_{sh}} s_w^{n/2} \quad \Rightarrow \quad s_w^{n/2} = \frac{A R_w (1-V_{sh})}{2 \phi_e^m} \, \Big( \sqrt{ \Big( \frac{V_{sh}}{R_{sh}} \Big)^2 + \frac{4\phi_e^m}{a R_t R_w (1-V_{sh}) } } - \frac{V_{sh}}{R_{sh}} \Big) |
with default value .
The dual-water model accounts for the fact that different shales have different shale-bound water saturation :
\phi_t = \phi_e + \phi_t s_{wb} |
so that formation water saturation is related to total water saturation as:
s_w = \frac{s_{wt} - s_{wb}}{ 1 - s_{wb}} |
Объем пород складывается из объема плотной матрицы пород и полного порового объема :
где
Полный поровый объем пород складывается из объема , занятого связанной глинами воды и объема , занятого свободными флюидами (водой и углеводородами):
где
Отсюда:
и Общий объем воды в порах складывается их связанной глинами воды и свободной воды в порах :
и выражатся через общий объем поры следующим образом:
откуда
и
|
Formation resistivity is given by the following correlation:
\frac{1}{R_t} = \phi_t^m s_{wt}^n \, \Big[ \frac{1}{R_w} + \frac{s_{wb}}{s_{wt}} \Big( \frac{1}{R_{wb}} - \frac{1}{R_w} \Big) \Big] \quad \Rightarrow \quad s_w = \frac{s_{wt} - s_{wb}}{ 1 - s_{wb}} |
where
shale-bound water saturation | |
total water saturation (shal-bound water and free-water) | |
specific electrical resisitvity of shale-bound water |
In simple case when all shales have the same properties, the shale-bound water saturation can be expressed through the shaliness as:
s_{wb} = \zeta_{wb} V_{sh} |
Formation resistivity is given by the following correlation:
\frac{1}{R_t} = \phi_t^m s_{wt}^n \, \Big[ \frac{1}{R_w} +\frac{B Q_V}{s_{wt}} \Big] |
which is similar to dual-water with complex parameter relating to:
B Q_V = s_{wb} \Big( \frac{1}{R_{wb}} - \frac{1}{R_w} \Big) |
In some opractical cases, the kaboiratiry data is available on and separately, but still need calibration on core data.
|
[1] https://www.spec2000.net/01-index.htm [2] http://petrowiki.org/Water_saturation_determination [3] http://www.ux.uis.no/~s-skj/ipt/Proceedings/SCA.1987-2004/1-SCA1998-07.pdf |