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Hydrodynamic traps: mapping (view source)
Revision as of 15:41, 30 January 2014
, 15:41, 30 January 2014Initial import
{{publication
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Critical elements of the petroleum system
| chapter = Formation fluid pressure and its application
| frompg = 5-1
| topg = 5-64
| author = Edward A. Beaumont, Forrest Fiedler
| link = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
==Mapping hydrodynamic traps==
Formation fluid pressure data are necessary for mapping prospective hydrodynamic traps. Combining formation fluid pressures with other data, such as density and subsea elevation, produces maps that help outline areas where hydrodynamic gradients may have created, destroyed, or modified traps.
===Procedure: mapping hydrodynamic traps===
Follow the steps listed in the table below to map the location of possible hydrodynamic traps.
{| class = "wikitable"
|-
! Step
! Action
|-
| 1
| Look for [[permeability]] barriers or hydrocarbon-free water levels using pressure-depth plots.
|-
| 2
| Calculate potentiometric values for each well using the formula H<sub>w</sub> = Z + (P/grad P). (See “Calculating H<sub>w</sub> ” below)
|-
| 3
| Make a water isopotential map with respect to oil or gas, using the formula for V,
:<math>\mbox{V} = \left(\frac{\rho_{\rm w}}{\rho_{\rm w} - \rho_{\rm hc}}\right)\mbox{H}_{\rm w}</math>
<break> </break> Note: Use gas density where gas is expected and oil density where oil is expected.
|-
| 4
| Make a gas or oil isopotential contour map using the formula for U where U = V – Z. The values for Z, the subsea elevation of the target aquifer, can be determined by simply overlaying a structure contour map on the water isopotential map and subtracting (see “Example” below).
|-
| 5
| Locate possible accumulations of hydrocarbons in hydrodynamic traps by locating the areas of low gas or oil potential. Locations should make sense in context with all other geologic data.
|}
===Calculating h<sub>w</sub>===
A critical step in mapping hydrodynamic traps in a target formation is making a water isopotential map (step 3 above). Before that can be done, however, one must calculate a potentiometric value for each well.
Calculate H<sub>w</sub> for each well using the formula
:<math>\mbox{H}_{\rm w} = \mbox{Z} + \frac{\mbox{P}}{\mbox{grad P}}</math>
where:
* Z = structural elevation of target formation
* P = measured fluid pressure in the formation
* grad P = static formation water pressure gradient
For grad P, use 0.435 psi/ft for areas where regional water is probably fresh and 0.465 psi/ft for areas where regional water is probably highly saline.
===Example: u<sub>0</sub> contours===
The map below shows oil in a hydrodynamic trap (shaded area). No oil could be trapped in the structure, represented by solid contours, without the aid of hydrodynamics. The bold contours with long dashes represent the isopotential of oil (labeled U<sub>0</sub>). To make U<sub>o</sub> contours, follow this procedure.
{| class = "wikitable"
|-
! Step
! Action
|-
| 1
| Subtract the structure of the target formation (Z) from the isopotential of water (V<sub>o</sub> ).
|-
| 2
| Plot the remainder at the intersection of the two sets of contours.
|-
| 3
| Draw contours of the values.
|}
[[file:formation-fluid-pressure-and-its-application_fig5-38.png|thumb|{{figure number|5-38}}. Copyright: Dahlberg, 1994; courtesy Springer-Verlag.]]
==See also==
* [[Hydrodynamics]]
* [[Basic hydrodynamics]]
* [[Hydrodynamic influence on trapping]]
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Critical elements of the petroleum system]]
[[Category:Formation fluid pressure and its application]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Critical elements of the petroleum system
| chapter = Formation fluid pressure and its application
| frompg = 5-1
| topg = 5-64
| author = Edward A. Beaumont, Forrest Fiedler
| link = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
==Mapping hydrodynamic traps==
Formation fluid pressure data are necessary for mapping prospective hydrodynamic traps. Combining formation fluid pressures with other data, such as density and subsea elevation, produces maps that help outline areas where hydrodynamic gradients may have created, destroyed, or modified traps.
===Procedure: mapping hydrodynamic traps===
Follow the steps listed in the table below to map the location of possible hydrodynamic traps.
{| class = "wikitable"
|-
! Step
! Action
|-
| 1
| Look for [[permeability]] barriers or hydrocarbon-free water levels using pressure-depth plots.
|-
| 2
| Calculate potentiometric values for each well using the formula H<sub>w</sub> = Z + (P/grad P). (See “Calculating H<sub>w</sub> ” below)
|-
| 3
| Make a water isopotential map with respect to oil or gas, using the formula for V,
:<math>\mbox{V} = \left(\frac{\rho_{\rm w}}{\rho_{\rm w} - \rho_{\rm hc}}\right)\mbox{H}_{\rm w}</math>
<break> </break> Note: Use gas density where gas is expected and oil density where oil is expected.
|-
| 4
| Make a gas or oil isopotential contour map using the formula for U where U = V – Z. The values for Z, the subsea elevation of the target aquifer, can be determined by simply overlaying a structure contour map on the water isopotential map and subtracting (see “Example” below).
|-
| 5
| Locate possible accumulations of hydrocarbons in hydrodynamic traps by locating the areas of low gas or oil potential. Locations should make sense in context with all other geologic data.
|}
===Calculating h<sub>w</sub>===
A critical step in mapping hydrodynamic traps in a target formation is making a water isopotential map (step 3 above). Before that can be done, however, one must calculate a potentiometric value for each well.
Calculate H<sub>w</sub> for each well using the formula
:<math>\mbox{H}_{\rm w} = \mbox{Z} + \frac{\mbox{P}}{\mbox{grad P}}</math>
where:
* Z = structural elevation of target formation
* P = measured fluid pressure in the formation
* grad P = static formation water pressure gradient
For grad P, use 0.435 psi/ft for areas where regional water is probably fresh and 0.465 psi/ft for areas where regional water is probably highly saline.
===Example: u<sub>0</sub> contours===
The map below shows oil in a hydrodynamic trap (shaded area). No oil could be trapped in the structure, represented by solid contours, without the aid of hydrodynamics. The bold contours with long dashes represent the isopotential of oil (labeled U<sub>0</sub>). To make U<sub>o</sub> contours, follow this procedure.
{| class = "wikitable"
|-
! Step
! Action
|-
| 1
| Subtract the structure of the target formation (Z) from the isopotential of water (V<sub>o</sub> ).
|-
| 2
| Plot the remainder at the intersection of the two sets of contours.
|-
| 3
| Draw contours of the values.
|}
[[file:formation-fluid-pressure-and-its-application_fig5-38.png|thumb|{{figure number|5-38}}. Copyright: Dahlberg, 1994; courtesy Springer-Verlag.]]
==See also==
* [[Hydrodynamics]]
* [[Basic hydrodynamics]]
* [[Hydrodynamic influence on trapping]]
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Critical elements of the petroleum system]]
[[Category:Formation fluid pressure and its application]]