Changes

==Interpret the Lithology==

==Interpret the Lithology==

[[File:Well_Log_Analysis_Fig-3.png|thumb|300px|Figure 3-The use of gamma ray log to determine the lithology (Railsback, 2011).]]

[[File:Well_Log_Analysis_Fig-3.png|thumb|300px|Figure 3-The use of gamma ray log to determine the lithology.<ref>Railsback (2011). Characteristics of wireline well logs in the petroleum industry.</ref>]]

The user will be able to interpret the lithology by using several logs, there are gamma ray, spontaneous potential, resistivity, and density log. Basically, a formation with high gamma ray reading indicates that it is a shaly or shale, when the low gamma ray reading indicates a clean formation (sand, carbonate, evaporite, etc.), lithology interpretation is very important in reservoir characterization because, if the lithology interpretation is already wrong, the other steps such as porosity and water saturation calculation will be a total mess.

The user will be able to interpret the lithology by using several logs, there are gamma ray, spontaneous potential, resistivity, and density log. Basically, a formation with high gamma ray reading indicates that it is a shaly or shale, when the low gamma ray reading indicates a clean formation (sand, carbonate, evaporite, etc.), lithology interpretation is very important in reservoir characterization because, if the lithology interpretation is already wrong, the other steps such as porosity and water saturation calculation will be a total mess.

==Calculate the Water Saturation==

==Calculate the Water Saturation==

There are so many methods to calculate water saturation, the user may use Archie’s (1942), Simandoux’s (1963), etc. which will use different formula for every one of them, but in this article, the author will use Simandoux’s (1963) method, to calculate the water saturation by using this method, the user will need to use the following formula:

There are so many methods to calculate water saturation, the user may use Archie’s,<ref>Archie, G. E. (1950). Introduction to petrophysics of reservoir rocks. AAPG Bulletin, 34(5), 943-961.</ref> Simandoux’s (1963), etc. which will use different formula for every one of them, but in this article, the author will use Simandoux’s (1963) method, to calculate the water saturation by using this method, the user will need to use the following formula:

:<math>\frac{1}{Rt} = \frac{Sw^2}{F \times Rw} + \frac{Vsh \times Sw}{Rsh}</math>

:<math>\frac{1}{Rt} = \frac{Sw^2}{F \times Rw} + \frac{Vsh \times Sw}{Rsh}</math>

where Rt is the true resistivity of the formation (deep resistivity), Rw is the formation water resistivity, Vsh is the shale volume, Rsh is the resistivity of shale, Rwe is the formation water

where Rt is the true resistivity of the formation (deep resistivity), Rw is the formation water resistivity, Vsh is the shale volume, Rsh is the resistivity of shale, Rwe is the formation water





resistivity (without thermal effect), BHT is the bottom hole temperature, Rmf is the mud filtrate resistivity, SP is the spontaneous potential log reading, F is the formation volume factor, a is the tortuosity factor, m is the cementation exponent, φ is the porosity, and Sw is the water saturation. To acquire the value of a and m, the user will need to create a pickett plot, but according to Asquith (1980), the reference value is shown in table 3.

resistivity (without thermal effect), BHT is the bottom hole temperature, Rmf is the mud filtrate resistivity, SP is the spontaneous potential log reading, F is the formation volume factor, a is the tortuosity factor, m is the cementation exponent, φ is the porosity, and Sw is the water saturation. To acquire the value of a and m, the user will need to create a pickett plot, but according to Asquith,<ref name=Asquith>Asquith, G. B., Krygowski, D., & Gibson, C. R. (2004). Basic well log analysis(Vol. 16). Tulsa: American Association of Petroleum Geologists.</ref> the reference value is shown in table 3.





{| class = wikitable

{| class = wikitable

|-

|-

|+ Table 3-Tortuosity factor (a) and cementation exponent (m) reference table (Asquith, 1980).

|+ Table 3-Tortuosity factor (a) and cementation exponent (m) reference table.<ref name=Asquith />

|-

|-

! Lithology || a (tortuosity factor) || m (cementation exponent)

! Lithology || a (tortuosity factor) || m (cementation exponent)

:<math>\sigma = \frac{\left (\frac{Vp}{Vs} \right )^2 - 1}{2 \left(\frac{Vp}{Vs} \right )^2 - 1}</math>

:<math>\sigma = \frac{\left (\frac{Vp}{Vs} \right )^2 - 1}{2 \left(\frac{Vp}{Vs} \right )^2 - 1}</math>

where Vp is the P-Wave velocity and Vs is the S-Wave velocity. According to Castagna et al (1985), Vp and Vs can be calculated by using this formula:

where Vp is the P-Wave velocity and Vs is the S-Wave velocity. According to Castagna et al,<ref>Castagna, J. P., Batzle, M. L., & Eastwood, R. L. (1985). Relationships between compressional-wave and shear-wave velocities in clastic silicate rocks.Geophysics, 50(4), 571-581.</ref> Vp and Vs can be calculated by using this formula:

:<math>Vp (km/s) = 5.81 - 9.42 \times \mathit{\Phi} s - 2.21 \times Vclay</math>

:<math>Vp (km/s) = 5.81 - 9.42 \times \mathit{\Phi} s - 2.21 \times Vclay</math>

{| class="wikitable"

{| class="wikitable"

|-

|-

|+ Table 4-Matrix and fluid transit time reference table (Schlumberger, 1972).

|+ Table 4-Matrix and fluid transit time reference table.<ref>Schlumberger Limited. (1984). Schlumberger log interpretation charts. Schlumberger.</ref>

|-

|-

! Lithology !! Value (μs/ft) !! Fluid !! Value (μs/ft)

! Lithology !! Value (μs/ft) !! Fluid !! Value (μs/ft)

</gallery>

</gallery>

==References==

==Sources==

* Ijasan, O., Torres-Verdín, C., & Preeg, W. E. (2013). Interpretation of porosity and fluid constituents from well logs using an interactive neutron-density matrix scale. Interpretation, 1(2), T143-T155.

* Ijasan, O., Torres-Verdín, C., & Preeg, W. E. (2013). Interpretation of porosity and fluid constituents from well logs using an interactive neutron-density matrix scale. Interpretation, 1(2), T143-T155.

* Tiab, D., & Donaldson, E. C. (2011). Petrophysics: theory and practice of measuring reservoir rock and fluid transport properties. Gulf professional publishing.

* Tiab, D., & Donaldson, E. C. (2011). Petrophysics: theory and practice of measuring reservoir rock and fluid transport properties. Gulf professional publishing.

* Jorgensen, D. G. (1989). Using geophysical logs to estimate porosity, water resistivity, and intrinsic permeability.

* Jorgensen, D. G. (1989). Using geophysical logs to estimate porosity, water resistivity, and intrinsic permeability.

* Doveton, J. H. (1986). Log analysis of subsurface geology: Concepts and computer methods.

* Doveton, J. H. (1986). Log analysis of subsurface geology: Concepts and computer methods.

* Ellis, D. V., & Singer, J. M. (2007). Well logging for earth scientists (Vol. 692). Dordrecht: Springer.

* Ellis, D. V., & Singer, J. M. (2007). Well logging for earth scientists (Vol. 692). Dordrecht: Springer.

* Muammar, R. (2014). Application of Fluid Mechanics to Determine Oil and Gas Reservoir’s Petrophysical Properties By Using Well Log Data.  

* Muammar, R. (2014). Application of Fluid Mechanics to Determine Oil and Gas Reservoir’s Petrophysical Properties By Using Well Log Data.  

* Balan, B., Mohaghegh, S., & Ameri, S. (1995). State-of-the-art in permeability determination from well log data: part 1-A comparative study, model development. paper SPE, 30978, 17-21.

* Balan, B., Mohaghegh, S., & Ameri, S. (1995). State-of-the-art in permeability determination from well log data: part 1-A comparative study, model development. paper SPE, 30978, 17-21.