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  = 9-38

  | 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_a) 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_a) 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_a==

==Horizontal and vertical k_a==

Horizontal K_a (i.e., parallel to bedding) is generally greater than vertical K_a (i.e., normal to bedding) because of vertical changes in sorting and because of bedding laminations. High vertical K_a generally results from fracturing or even burrowing that cuts across bedding. Most K_a calculations are made from measurements of horizontal plugs.

Horizontal K_a (i.e., parallel to bedding) is generally greater than vertical K_a (i.e., normal to bedding) because of vertical changes in [[Core_description#Maturity|sorting]] and because of bedding laminations. High vertical K_a generally results from fracturing or even burrowing that cuts across bedding. Most K_a calculations are made from measurements of horizontal plugs.

==Steady-state permeability equation==

==Steady-state permeability equation==

[[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

* P₁ = pressure at input end, atm

* P₁ = pressure at input end, atm

* P₂ = pressure at output end, atm

* P₂ = pressure at output end, atm

* μ = air viscosity, cp

* μ = air [[viscosity]], cp

 

[[file:predicting-reservoir-system-quality-and-performance_fig9-24.png|thumb|{{figure number|9-24}}See text for explanation.]]

The diagram of a plug in [[:file:predicting-reservoir-system-quality-and-performance_fig9-24.png|Figure 1]] illustrates some of these variables.

==Limitations of darcy's equation==

==Limitations of darcy's equation==

==Example==

==Example==

In the photos below, 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_a 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_a 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_a 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_a will be lower (by using the same A).

Flow unit 1 has a [[porosity]] of 30%, and flow unit 2 has a porosity of 10%. The variance in porosity becomes the indicator of the contrast in pore throat size when converted to port size. For flow unit 1, the port size is approximately 1.1μ; for flow unit 2, port size is approximately 3μ.

Flow unit 1 has a [[porosity]] of 30%, and flow unit 2 has a porosity of 10%. The variance in porosity becomes the indicator of the contrast in pore throat size when converted to port size. For flow unit 1, the port size is approximately 1.1μ; for flow unit 2, port size is approximately 3μ.

==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]]