Changes

Analyzing air [[permeability]] (K_a and [[porosity]] (Φ) data separately to characterize rock quality can be deceiving. Analyzing K_a and Φ data using the K_a/Φ ratio or the r₃₅ method<ref name=ch09r46>Pittman, E., D., 1992, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0076/0002/0000/0191.htm Relationship of porosity to permeability to various parameters derived from mercury injection–capillary pressure curves for sandstone]: AAPG Bulletin, vol. 76, no. 2, p. 191–198.</ref> is much more effective for determining quality. The K_a/Φ ratio or the r₃₅ method yields information about the fluid flow and storage quality of a rock.

Analyzing air [[permeability]] (K_a and [[porosity]] (Φ) data separately to characterize rock quality can be deceiving. Analyzing K_a and Φ data using the K_a/Φ ratio or the r₃₅ method<ref name=ch09r46>Pittman, E., D., 1992, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0076/0002/0000/0191.htm Relationship of porosity to permeability to various parameters derived from mercury injection–capillary pressure curves for sandstone]: AAPG Bulletin, vol. 76, no. 2, p. 191–198.</ref> is much more effective for determining quality. The K_a/Φ ratio or the r₃₅ method yields information about the fluid flow and storage quality of a rock.

[[file:predicting-reservoir-system-quality-and-performance_fig9-16.png|thumb|{{figure number|1}}See text for explanation.]]

 

[[file:predicting-reservoir-system-quality-and-performance_fig9-16.png|thumb|{{figure number|1}}SEM microphotographs.]]

Using K_a and Φ data separately to characterize reservoir rock quality is misleading. Consider the rocks shown in the SEM microphotographs in [[:file:predicting-reservoir-system-quality-and-performance_fig9-16.png|Figure 1]]. Flow unit 1 is a mesoporous, sucrosic dolomite. Its average Φ is 30% and average K_a is 10 md. Flow unit 2 is a macroporous, oolitic limestone. Its average Φ is 10% and average K_a is 10 md.

Using K_a and Φ data separately to characterize reservoir rock quality is misleading. Consider the rocks shown in the SEM microphotographs in [[:file:predicting-reservoir-system-quality-and-performance_fig9-16.png|Figure 1]]. Flow unit 1 is a mesoporous, sucrosic dolomite. Its average Φ is 30% and average K_a is 10 md. Flow unit 2 is a macroporous, oolitic limestone. Its average Φ is 10% and average K_a is 10 md.

In [[:file:predicting-reservoir-system-quality-and-performance_fig9-16.png|Figure 1]], flow unit 1 has a K_a/Φ value of 33 and flow unit 2 has a K_a/Φ value of 100. Even though Φ is greater and K_a is the same for flow unit 1, the lower K_a/Φ value indicates its quality is lower than flow unit 2.

In [[:file:predicting-reservoir-system-quality-and-performance_fig9-16.png|Figure 1]], flow unit 1 has a K_a/Φ value of 33 and flow unit 2 has a K_a/Φ value of 100. Even though Φ is greater and K_a is the same for flow unit 1, the lower K_a/Φ value indicates its quality is lower than flow unit 2.

[[file:predicting-reservoir-system-quality-and-performance_fig9-17.png|thumb|{{figure number|2}}See text for explanation.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-17.png|thumb|{{figure number|2}}See text for explanation.]]

On the plot in [[:file:predicting-reservoir-system-quality-and-performance_fig9-17.png|Figure 2]], the contours represent a constant K_a/Φ ratio and divide the plot into areas of similar pore types. Data points that plot along a constant ratio have similar flow quality across a large range of porosity and/or permeability. The clusters of points on the plot  in [[:file:predicting-reservoir-system-quality-and-performance_fig9-17.png|Figure 2]] represent hypothetical K_a/Φ values for flow units 1 and 2 presented in [[:file:predicting-reservoir-system-quality-and-performance_fig9-16.png|Figure 1]]. The position of the clusters relative to the K_a/Φ contours indicates flow unit 2 has higher quality in terms of K_a/Φ ratio than flow unit 1.

On the plot in [[:file:predicting-reservoir-system-quality-and-performance_fig9-17.png|Figure 2]], the contours represent a constant K_a/Φ ratio and divide the plot into areas of similar pore types. Data points that plot along a constant ratio have similar flow quality across a large range of porosity and/or permeability. The clusters of points on the plot  in [[:file:predicting-reservoir-system-quality-and-performance_fig9-17.png|Figure 2]] represent hypothetical K_a/Φ values for flow units 1 and 2 presented i in [[:file:predicting-reservoir-system-quality-and-performance_fig9-16.png|Figure 1]]. The position of the clusters relative to the K_a/Φ contours indicates flow unit 2 has higher quality in terms of K_a/Φ ratio than flow unit 1.

==What is r₃₅?==

==What is r₃₅?==

H.D. Winland of Amoco used mercury injection-capillary pressure curves to develop an empirical relationship among Φ, K_a, and pore throat radius (r). He tested 312 different water-wet samples. The data set included 82 samples (56 sandstone and 26 carbonate) with low permeability corrected for gas slippage and 240 other uncorrected samples. Winland found that the effective pore system that dominates flow through a rock corresponds to a mercury saturation of 35%. That pore system has pore throat radii (called port size, or r₃₅) equal to or smaller than the pore throats entered when a rock is saturated 35% with a nonwetting phase. After 35% of the pore system fills with a non-wetting phase fluid, the remaining pore system does not contribute to flow. Instead, it contributes to storage.

H.D. Winland of Amoco used mercury injection-capillary pressure curves to develop an empirical relationship among Φ, K_a, and pore throat radius (r). He tested 312 different water-wet samples. The data set included 82 samples (56 sandstone and 26 carbonate) with low permeability corrected for gas slippage and 240 other uncorrected samples. Winland found that the effective pore system that dominates flow through a rock corresponds to a mercury saturation of 35%. That pore system has pore throat radii (called port size, or r₃₅) equal to or smaller than the pore throats entered when a rock is saturated 35% with a nonwetting phase. After 35% of the pore system fills with a non-wetting phase fluid, the remaining pore system does not contribute to flow. Instead, it contributes to storage.

Pittman<ref name=ch09r46 />) speculates, “Perhaps Winland found the best correlation to be r₃₅ because that is where the average modal pore aperture occurs and where the pore network is developed to the point of serving as an effective pore system that dominates flow.” The capillary pressure curve and pore throat size histogram in [[:file:predicting-reservoir-system-quality-and-performance_fig9-18.png|Figure 3]] illustrate Pittman's point.

Pittman<ref name=ch09r46 /> speculates, “Perhaps Winland found the best correlation to be r₃₅ because that is where the average modal pore aperture occurs and where the pore network is developed to the point of serving as an effective pore system that dominates flow.” The capillary pressure curve and pore throat size histogram in [[:file:predicting-reservoir-system-quality-and-performance_fig9-18.png|Figure 3]] illustrate Pittman's point.

==The winland r₃₅ equation==

==The winland r₃₅ equation==