Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Predicting reservoir system quality and performance

  | chapter = Predicting reservoir system quality and performance

  | frompg  = 9-1

  | frompg  = 9-29

  | topg    = 9-156

  | topg    = 9-33

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

[[file:predicting-reservoir-system-quality-and-performance_fig9-16.png|300px|thumb|{{figure number|1}}SEM microphotographs.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-16.png|300px|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 [[Wikipedia:Mesoporous material|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.

Initially, we might think that flow unit 1 is higher quality because it has three times more porosity and the same permeability as flow unit 2. However, in terms of fluid flow efficiency and storage, as shown by the K_a/Φ ratio or r₃₅, flow unit 2 is actually the better rock.

Initially, we might think that flow unit 1 is higher quality because it has three times more porosity and the same permeability as flow unit 2. However, in terms of fluid flow efficiency and storage, as shown by the K_a/Φ ratio or r₃₅, flow unit 2 is actually the better rock.

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==

Winland<ref name=ch09r70>Winland, H., D., 1972, Oil accumulation in response to pore size changes, Weyburn field, Saskatchewan: Amoco Production Company Report F72-G-25, 20 p. (unpublished).</ref><ref name=ch09r71>Winland, H., D., 1976, Evaluation of gas slippage and pore aperture size in carbonate and sandstone reservoirs: Amoco Production Company Report F76-G-5, 25 p. (unpublished).</ref> developed the following equation to calculate r₃₅ for samples with intergranular or intercrystalline porosity:

Winland<ref name=ch09r70>Winland, H., D., 1972, Oil accumulation in response to pore size changes, Weyburn field, Saskatchewan: Amoco Production Company Report F72-G-25, 20 p. (unpublished).</ref><ref name=ch09r71>Winland, H., D., 1976, Evaluation of gas slippage and pore aperture size in carbonate and sandstone reservoirs: Amoco Production Company Report F76-G-5, 25 p. (unpublished).</ref> developed the following equation to calculate r₃₅ for samples with intergranular or intercrystalline porosity:

==Characterizing rock quality with r₃₅==

==Characterizing rock quality with r₃₅==

[[file:predicting-reservoir-system-quality-and-performance_fig9-19.png|thumb|{{figure number|4}}K_a/Φ plot.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-19.png|300px|thumb|{{figure number|4}}K_a/Φ plot.]]

Rock quality is easily characterized using r₃₅. Consider the clusters of points representing flow units 1 and 2 ([[:file:predicting-reservoir-system-quality-and-performance_fig9-16.png|Figure 1]]) on the K_a/Φ plot in [[:file:predicting-reservoir-system-quality-and-performance_fig9-19.png|Figure 4]]. The diagonal curved lines represent equal r₃₅ values. Points plotting along the same lines represent rocks with similar r₃₅ values and have similar quality. By interpolation, r₃₅ for flow unit 1 is approximately 1.1μ, and r₃₅ for flow unit 2 is approximately 3μ. The r₃₅ in flow unit 2 is almost three times as large as flow unit 1. Therefore, flow unit 2 has better flow quality.

Rock quality is easily characterized using r₃₅. Consider the clusters of points representing flow units 1 and 2 ([[:file:predicting-reservoir-system-quality-and-performance_fig9-16.png|Figure 1]]) on the K_a/Φ plot in [[:file:predicting-reservoir-system-quality-and-performance_fig9-19.png|Figure 4]]. The diagonal curved lines represent equal r₃₅ values. Points plotting along the same lines represent rocks with similar r₃₅ values and have similar quality. By interpolation, r₃₅ for flow unit 1 is approximately 1.1μ, and r₃₅ for flow unit 2 is approximately 3μ. The r₃₅ in flow unit 2 is almost three times as large as flow unit 1. Therefore, flow unit 2 has better flow quality.

==Example capillary pressure curves==

==Example capillary pressure curves==

 

[[file:predicting-reservoir-system-quality-and-performance_fig9-20.png|thumb|{{figure number|5}}Hypothetical capillary pressure curves.]]

file:predicting-reservoir-system-quality-and-performance_fig9-20.png|{{figure number|5}}Hypothetical capillary pressure curves.

Hypothetical capillary pressure curves can be drawn by using r₃₅ as a point on the curve. The capillary pressure curves below are hypothetical curves for the example presented in [[:file:predicting-reservoir-system-quality-and-performance_fig9-19.png|Figure 4]]. The curves demonstrate that entry pressures for flow unit 2 are less than those for flow unit 1; therefore, fluid flow in flow unit 2 is more efficient. In [[:file:predicting-reservoir-system-quality-and-performance_fig9-20.png|Figure 5]], it takes [[length::28 ft]] of oil column for oil to enter 35% of pore space of flow unit 2 and [[length::70 ft]] to enter 35% of pore space of flow unit 1.

Hypothetical capillary pressure curves can be drawn by using r₃₅ as a point on the curve. The capillary pressure curves below are hypothetical curves for the example presented in [[:file:predicting-reservoir-system-quality-and-performance_fig9-19.png|Figure 4]]. The curves demonstrate that entry pressures for flow unit 2 are less than those for flow unit 1; therefore, fluid flow in flow unit 2 is more efficient. In [[:file:predicting-reservoir-system-quality-and-performance_fig9-20.png|Figure 5]], it takes [[length::28 ft]] of oil column for oil to enter 35% of pore space of flow unit 2 and [[length::70 ft]] to enter 35% of pore space of flow unit 1.

===Example relative permeability curves===

===Example relative permeability curves===

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting reservoir system quality and performance]]

[[Category:Predicting reservoir system quality and performance]]