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==Reservoir and Non-reservoir Lithology Discrimination==

==Reservoir and Non-reservoir Lithology Discrimination==

Reservoirs have distinctively different elastic properties compared to the non-reservoirs (shales, claystones, wet sands, etc.). An example from clastic gas reservoir is shown on Figure 1, where Sand A (clean sandstone) and Sand B (clayey sandstone as indicated by gamma ray log) have different density and wave velocities compared to the claystones, even Sand A and Sand B have different properties due to the presence of clays in Sand B.

Reservoirs have distinctively different elastic properties compared to the non-reservoirs (shales, claystones, wet sands, etc.). An example from clastic gas reservoir is shown on [[:File:GeoWikiWriteOff2021-Muamamr-Figure1.png|Figure 1]], where Sand A (clean sandstone) and Sand B (clayey sandstone as indicated by gamma ray log) have different density and wave velocities compared to the claystones, even Sand A and Sand B have different properties due to the presence of clays in Sand B.

   

   

In order to thoroughly discriminate the reservoir and non-reservoir lithology, the dataset should be derived into but not limited to the following properties:<ref name="1Goodwayetal">Goodway, B., T. Chen, and J. Downton, 1997, Improved AVO Fluid Detection and Lithology Discrimination using Lamé Petrophysical Parameters; “λρ”, “μρ”, and “λ/μ fluid stack”, from P and S Inversions: SEG Technical Program Expanded Abstracts, p. 183-186.</ref>

In order to thoroughly discriminate the reservoir and non-reservoir lithology, the dataset should be derived into but not limited to the following properties:<ref name="1Goodwayetal">Goodway, B., T. Chen, and J. Downton, 1997, Improved AVO Fluid Detection and Lithology Discrimination using Lamé Petrophysical Parameters; “λρ”, “μρ”, and “λ/μ fluid stack”, from P and S Inversions: SEG Technical Program Expanded Abstracts, p. 183-186.</ref>

::<math>MR = (V_s * Rho)^2 = SI^2</math>

::<math>MR = (V_s * Rho)^2 = SI^2</math>

::as MR is strongly controlled by the shear impedance (SI) and shear modulus (μ), the magnitude of this property does not really affected by pore fluids, but rather by the lithology.  

::as MR is strongly controlled by the shear impedance (SI) and shear modulus (μ), the magnitude of this property does not really affected by pore fluids, but rather by the lithology.  

[[File:GeoWikiWriteOff2021-Muamamr-Figure1.png|thumbnail|Figure 1. Well log section showing the difference of rock physics properties between clean sandstone (Sand A), clayey sandstone (Sand B), and claystone. ]]

[[File:GeoWikiWriteOff2021-Muamamr-Figure1.png|framed|center|{{Figure number|1}}Well log section showing the difference of rock physics properties between clean sandstone (Sand A), clayey sandstone (Sand B), and claystone.]]

As the available dataset is composed of gas saturated sands, one can model the expected elastic properties under wet condition by utilizing Gassmann’s Fluid Substitution[2], [3]). The result of fluid substitution on Sand A and Sand B are shown on Figure 2. It can be observed that wet sands are acoustically harder (higher Vp and Rho, but with minor change in Vs) compared to gas sands, some of these wet sands are acoustically harder than the claystones.  

As the available dataset is composed of gas saturated sands, one can model the expected elastic properties under wet condition by utilizing Gassmann’s Fluid Substitution[2], [3]). The result of fluid substitution on Sand A and Sand B are shown on Figure 2. It can be observed that wet sands are acoustically harder (higher Vp and Rho, but with minor change in Vs) compared to gas sands, some of these wet sands are acoustically harder than the claystones.