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  = 9-23

  | topg    = 9-156

  | topg    = 9-25

  | 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

:<math>\mbox{P}_{\rm c} = \frac{2\gamma \cos \Theta}{\mbox{r}}</math>

:<math>\mbox{P}_{\rm c} = \frac{2\gamma \cos \Theta}{\mbox{r}}</math>

This expression assumes the capillary phenomenon occurs within a tube with a circular cross section. Real pores only approximate this, and then only if they are intergranular or intercrystalline (Coalson, personal communication, 1997).

This expression assumes the capillary phenomenon occurs within a tube with a circular [[cross section]]. Real pores only approximate this, and then only if they are intergranular or inter crystalline.<ref name=CoalsonPC>Coalson, personal communication, 1997</ref>

==Capillary test procedure==

==Capillary test procedure==

In a mercury capillary pressure test, a rock with a measured [[porosity]] is immersed in a mercury pressure cell. The pressure in the cell is raised to a predetermined pressure level (P1, figure below). When the cell comes to equilibrium, the volume of injected mercury is measured (V2). Since the porosity of the test sample is known prior to the test, the volume of injected mercury can be converted to the percent of the total pore volume filled with mercury (for example, 10% at [[pressure::10 psi]] for point M1). All the pores filled with mercury at this point in the test have at least one 10μ pore throat radius or larger and represent 10% of the sample's pore volume. This procedure is repeated several more times at different pressures (for example, points M2 through M5).

 

 

In a mercury capillary pressure test, a rock with a measured [[porosity]] is immersed in a mercury pressure cell. The pressure in the cell is raised to a predetermined pressure level (P1, [[:file:predicting-reservoir-system-quality-and-performance_fig9-11.png|Figure 1]]). When the cell comes to equilibrium, the volume of injected mercury is measured (V2). Since the porosity of the test sample is known prior to the test, the volume of injected mercury can be converted to the percent of the total pore volume filled with mercury (for example, 10% at [[pressure::10 psi]] for point M1). All the pores filled with mercury at this point in the test have at least one 10μ pore throat radius or larger and represent 10% of the sample's pore volume. This procedure is repeated several more times at different pressures (for example, points M2 through M5).

==Pore throat profiles==

==Pore throat profiles==

[[file:predicting-reservoir-system-quality-and-performance_fig9-11.png|thumb|{{figure number|9-11}}See text for explanation.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-12.png|300px|thumb|{{figure number|2}}Curve drawn through the points in Figure 1.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-12.png|thumb|{{figure number|9-12}}See text for explanation.]]

A curve is drawn through the measured points at test completion. This capillary pressure curve also represents a pore throat size profile for the tested sample. It relates a given pore throat size to its capillary resistance (P_c). [[:file:predicting-reservoir-system-quality-and-performance_fig9-12.png|Figure 2]] shows the curve drawn through the points in [[:file:predicting-reservoir-system-quality-and-performance_fig9-11.png|Figure 1]].

==Converting capillary pressure to pore throat size==

==Converting capillary pressure to pore throat size==

:<math>\mbox{r} = \frac{2\gamma \cos \Theta}{\mbox{P}_{\rm c}}</math>

:<math>\mbox{r} = \frac{2\gamma \cos \Theta}{\mbox{P}_{\rm c}}</math>

Capillary pressure for a given S_w can also be converted to an approximation of height above free water (''h'') within a reservoir system. From a capillary pressure curve at a given S_w, we read the capillary pressure and multiply it by a factor that converts P_c to [[buoyancy pressure]] (P_b). If the conversion factor is not known, we use 0.4 for gas and 0.7 for oil.

Capillary pressure for a given S_w can also be converted to an approximation of height above [[free water level|free water]] (''h'') within a reservoir system. From a capillary pressure curve at a given S_w, we read the capillary pressure and multiply it by a factor that converts P_c to [[buoyancy pressure]] (P_b). If the conversion factor is not known, we use 0.4 for gas and 0.7 for oil.

==Using p_c to estimate ''h'' and ''r''==

==Using p_c to estimate ''h'' and ''r''==

{| class = "wikitable"

{| class = "wikitable"

|-

|-

! To estimate

! To estimate || Follow this procedure

! Follow this procedure

|-

|-

| Pore throat size ( ''r'' ) from S_w

| Pore throat size ( ''r'' ) from S_w

| *  <table-wrap id="ch09utbl12a" position="float"> <table frame="hsides"> <colgroup> <col align="left"></col> <col align="left"></col> </colgroup> <thead> <tr> <th align="left"> Step </th> <th align="center"> Action </th> </tr> </thead> <tbody> <tr> <td align="center"> 1 Enter the X-axis at percent pore volume (S_w value). </td></tr> <tr> 2 At the intersectionof grid line and P_c curve, read the corresponding value for ''r'' on the Y-axis </tr> </tbody> </table> </table-wrap>

|

 

# Enter the X-axis at percent pore volume (S_w value).

# At the intersectionof grid line and P_c curve, read the corresponding value for ''r'' on the Y-axis

|-

|-

| <th align="left"> Step</th>

| Height above free water level (''h'') from S_w

| <th align="center"> Action</th>

|  

# Enter the X-axis at percent pore volume (S_w value).

# At the intersectionof grid line and P_c curve, read the corresponding value for P_c on the left Y-axis

| Enter the X-axis at percent pore volume (S_w value).

| At the intersectionof grid line and P_c curve, read the corresponding value for ''r'' on the Y-axis

|}

|}

<tr><td align="left" valign="top">Height above free water level (''h'') from S_w</td><td align="center">

==Example==

Using the curve in [[:file:predicting-reservoir-system-quality-and-performance_fig9-13.png|Figure 3]], if S_w = 20% (point 1), then the mercury capillary pressure (P_c) that must be overcome to enter pore throats at that point on the curve is [[pressure::200 psi]] (point 2). Converting mercury P_c to [[hydrocarbon column]] height (''h''):

|-

|-

| Enter the X-axis at percent pore volume (S_w value).

|-

| At the intersection of grid line and P_c curve, read the corresponding value for P_c on the left Y-axis.

| 3

 

 

Using the curve in the diagram below, if S_w = 20% (point 1), then the mercury capillary pressure (P_c) that must be overcome to enter pore throats at that point on the curve is [[pressure::200 psi]] (point 2). Converting mercury P_c to hydrocarbon column height (''h''):

:<math>\mbox{h}  = 200 \mbox{ psi} \times 0.7 = 140 \mbox{ ft of oil column}</math>

:<math>\mbox{h}  = 200 \mbox{ psi} \times 0.7 = 140 \mbox{ ft of oil column}</math>

:<math>&=200 \mbox{ psi} \times 0.4 = 50 \mbox{ ft of gas column}</math>

:<math>\mbox{h}  =200 \mbox{ psi} \times 0.4 = 50 \mbox{ ft of gas column}</math>

The minimum pore throat radius entered when S_w is 20% and P_c is [[pressure::200 psi]] is 0.5μ.

The minimum pore throat radius entered when S_w is 20% and P_c is [[pressure::200 psi]] is 0.5μ.

==See also==

==See also==

* [[Classifying pore systems]]

* [[Pore systems]]

* [[Pore system fundamentals]]

* [[Pore system fundamentals]]

* [[Pore system shapes]]

* [[Pore system shapes]]

* [[Pore and pore throat sizes]]

* [[Pore and pore throat sizes]]

* [[Connectivity and pore throat size]]

* [[Pore throat size and connectivity]]

 

==External links==

==External links==

[[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]]