Changes

==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 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[1]:  

In order to thoroughly discriminate the reservoir and non-reservoir lithology, the dataset should be derived into but not limited to the following properties[1]:  

AI (acoustic impedance)= this property is sensitive towards the change in lithology and fluid content. Gas has the lowest AI as it is acoustically softer compared to water, whereas oil sits in between. As this property is directly affected by the change in compaction and/or diagenetic processes, its sensitivity decreases under specific circumstances and may be unable to differentiate between each lithology.  

# ''AI'' (acoustic impedance) = this property is sensitive towards the change in lithology and fluid content. Gas has the lowest AI as it is acoustically softer compared to water, whereas oil sits in between. As this property is directly affected by the change in compaction and/or diagenetic processes, its sensitivity decreases under specific circumstances and may be unable to differentiate between each lithology.  

AI=V_p*Rho

AI=V_p*Rho

Vp/Vs (velocity ratio)= sensitive towards the change in fluid content even between wet and hydrocarbon bearing sandstones as Vp generally drops due to the presence of gas or oil however, the Vs does not affected much and therefore will produce low Vp/Vs. Velocity ratio is mathematically defined as follow:  

# ''V_p/V_s'' (velocity ratio)= sensitive towards the change in fluid content even between wet and hydrocarbon bearing sandstones as Vp generally drops due to the presence of gas or oil however, the Vs does not affected much and therefore will produce low Vp/Vs. Velocity ratio is mathematically defined as follow:  

V_p/V_s=V_p/V_s  

V_p/V_s=V_p/V_s  

LR (lambda-rho)= good fluid indicator as it is sensitive to the change in fluid content. Lambda (Lamé parameter) is defined as fluid incompressibility, where gas has the lowest LR as it is highly compressible and least dense, water has the highest LR, whereas oil sits in between. LR is mathematically defined as follow:  

# ''LR'' (lambda-rho)= good fluid indicator as it is sensitive to the change in fluid content. Lambda (Lamé parameter) is defined as fluid incompressibility, where gas has the lowest LR as it is highly compressible and least dense, water has the highest LR, whereas oil sits in between. LR is mathematically defined as follow:  

LR=〖(V_p*Rho)〗^2-〖2(V_s*Rho)〗^2=〖AI〗^2-2〖SI〗^2

LR=〖(V_p*Rho)〗^2-〖2(V_s*Rho)〗^2=〖AI〗^2-2〖SI〗^2

MR (mu-rho)= this property is sensitive towards the change in lithology. Sandstones generally have higher MR compared to shales and claystones due to its higher rigidity (μ). MR is mathematically defined as follow:  

# ''MR'' (mu-rho)= this property is sensitive towards the change in lithology. Sandstones generally have higher MR compared to shales and claystones due to its higher rigidity (μ). MR is mathematically defined as follow:  

MR=〖(V_s*Rho)〗^2=〖SI〗^2

MR=〖(V_s*Rho)〗^2=〖SI〗^2

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.