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added Category:Treatise Handbook 3 using HotCat
| 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 = 9-38
| topg = 9-156
| topg = 9-39
| 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
| isbn = 0-89181-602-X
| isbn = 0-89181-602-X
}}
}}
Absolute [[permeability]] (K<sub>a</sub>) is the property of a rock that characterizes the flow of fluid through its interconnected pores. It is a measure of the fluid conductivity of a rock. The permeability of a flow unit in a reservoir is not an absolute value but is a relative value that varies with water saturation (''see'' “Relative [[Permeability]] and Pore Type” following). Understanding the methodology for permeability measurements is important for understanding how to assess reservoir rock quality or to compare the quality of one flow unit to another.
Absolute [[permeability]] (K<sub>a</sub>) is the property of a rock that characterizes the flow of fluid through its interconnected pores. It is a measure of the fluid conductivity of a rock. The permeability of a flow unit in a reservoir is not an absolute value but is a relative value that varies with water saturation (see [[Relative permeability and pore type]]). Understanding the methodology for permeability measurements is important for understanding how to assess reservoir rock quality or to compare the quality of one flow unit to another.
==Horizontal and vertical k<sub>a</sub>==
==Horizontal and vertical k<sub>a</sub>==
Horizontal K<sub>a</sub> (i.e., parallel to bedding) is generally greater than vertical K<sub>a</sub> (i.e., normal to bedding) because of vertical changes in sorting and because of bedding laminations. High vertical K<sub>a</sub> generally results from fracturing or even burrowing that cuts across bedding. Most K<sub>a</sub> calculations are made from measurements of horizontal plugs.
Horizontal K<sub>a</sub> (i.e., parallel to bedding) is generally greater than vertical K<sub>a</sub> (i.e., normal to bedding) because of vertical changes in [[Core_description#Maturity|sorting]] and because of bedding laminations. High vertical K<sub>a</sub> generally results from fracturing or even burrowing that cuts across bedding. Most K<sub>a</sub> calculations are made from measurements of horizontal plugs.
==Steady-state permeability equation==
==Steady-state permeability equation==
[[file:predicting-reservoir-system-quality-and-performance_fig9-24.png|thumb|{{figure number|1}}See text for explanation.]]
[[file:predicting-reservoir-system-quality-and-performance_fig9-24.png|300px|thumb|{{figure number|1}}Illustration of variables.]]
[[Permeability]] is not measured; it is calculated. The steady-state equation for calculating permeability (using an integrated form of Darcy's law) is
[[Permeability]] is not measured; it is calculated. The steady-state equation for calculating permeability (using an integrated form of Darcy's law) is
* P<sub>1</sub> = pressure at input end, atm
* P<sub>1</sub> = pressure at input end, atm
* P<sub>2</sub> = pressure at output end, atm
* P<sub>2</sub> = pressure at output end, atm
* μ = air viscosity, cp
* μ = air [[viscosity]], cp
The diagram of a plug in [[:file:predicting-reservoir-system-quality-and-performance_fig9-24.png|Figure 1]] illustrates some of these variables.
The diagram of a plug in [[:file:predicting-reservoir-system-quality-and-performance_fig9-24.png|Figure 1]] illustrates some of these variables.
==Example==
==Example==
[[file:predicting-reservoir-system-quality-and-performance_fig9-25.png|thumb|{{figure number|2}}See text for explanation.]]
[[file:predicting-reservoir-system-quality-and-performance_fig9-25.png|400px|thumb|{{figure number|2}}Two flow units.]]
In [[:file:predicting-reservoir-system-quality-and-performance_fig9-25.png|Figure 2]], flow unit 1 is a sucrosic dolomite. On a face of a plug of flow unit 1, a very large number of very small pore throats (capillaries) occur, resulting in a measurable flow (Q). That Q, at a measured cross-sectional area A of the plug, yields a K<sub>a</sub> of approximately 20 md.
In [[:file:predicting-reservoir-system-quality-and-performance_fig9-25.png|Figure 2]], flow unit 1 is a sucrosic [[dolomite]]. On a face of a plug of flow unit 1, a very large number of very small pore throats (capillaries) occur, resulting in a measurable flow (Q). That Q, at a measured cross-sectional area A of the plug, yields a K<sub>a</sub> of approximately 20 md.
The sample from flow unit 2 with the same A has fewer, larger pore throats (capillaries) exposed in the face of the plug. If the Q for flow unit 2 is slightly lower than flow unit 1, then the K<sub>a</sub> will be lower (by using the same A).
The sample from flow unit 2 with the same A has fewer, larger pore throats (capillaries) exposed in the face of the plug. If the Q for flow unit 2 is slightly lower than flow unit 1, then the K<sub>a</sub> will be lower (by using the same A).
==See also==
==See also==
* [[Pore–fluid interaction]]
* [[Pore-fluid interaction]]
* [[Hydrocarbon expulsion, migration, and accumulation]]
* [[Hydrocarbon expulsion, migration, and accumulation]]
* [[Characterizing rock quality]]
* [[Characterizing rock quality]]
[[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]]
[[Category:Treatise Handbook 3]]