Difference between revisions of "Pickett plot construction"

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  | 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
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  | frompg  = 9-1
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  | frompg  = 9-60
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  | topg    = 9-156
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  | topg    = 9-63
 
  | 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
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A Pickett plot lets us compare water saturations of different parts of a reservoir in one or many wells. The Pickett plot<ref name=ch09r45>Pickett, G., R., 1973, Pattern recognition as a means of formation evaluation: The Log Analyst, vol. 14, no. 4, p. 3–11.</ref> is a visual representation of the [[Archie equation]]<ref name=Archie_1942>Archie, G. E., 1942, The electrical resistivity log as an aid in determining some reservoir characteristics: Petroleum Transactions of AIME 146: 54–62.</ref> and therefore is a powerful graphic technique for estimating S<sub>w</sub> ranges within a reservoir. All that is needed to make a Pickett plot is a set of porosities and corresponding resistivities taken from well logs and 2×4 cycle log-log paper. The procedure for making a Pickett plot consists of five steps, detailed below.
 
A Pickett plot lets us compare water saturations of different parts of a reservoir in one or many wells. The Pickett plot<ref name=ch09r45>Pickett, G., R., 1973, Pattern recognition as a means of formation evaluation: The Log Analyst, vol. 14, no. 4, p. 3–11.</ref> is a visual representation of the [[Archie equation]]<ref name=Archie_1942>Archie, G. E., 1942, The electrical resistivity log as an aid in determining some reservoir characteristics: Petroleum Transactions of AIME 146: 54–62.</ref> and therefore is a powerful graphic technique for estimating S<sub>w</sub> ranges within a reservoir. All that is needed to make a Pickett plot is a set of porosities and corresponding resistivities taken from well logs and 2×4 cycle log-log paper. The procedure for making a Pickett plot consists of five steps, detailed below.
  
−
{| class = "wikitable"
+
# Plot points of matching [[porosity]] and true resistivity (R<sub>t</sub> ) on log-log paper.
−
|-
+
# Plot R<sub>w</sub> point on the R<sub>t</sub> scale.
−
! Step
+
# Determine ''m'' using the table of values.
−
! Action
+
# Plot the 100% S<sub>w</sub> line.
−
|-
+
# Plot the lines representing lower values of S<sub>w</sub> .
−
| 1
 
−
| Plot points of matching [[porosity]] and true resistivity (R<sub>t</sub> ) on log-log paper.
 
−
|-
 
−
| 2
 
−
| Plot R<sub>w</sub> point on the R<sub>t</sub> scale.
 
−
|-
 
−
| 3
 
−
| Determine ''m'' using the table of values.
 
−
|-
 
−
| 4
 
−
| Plot the 100% S<sub>w</sub> line.
 
−
|-
 
−
| 5
 
−
| Plot the lines representing lower values of S<sub>w</sub> .
 
−
|}
 
  
 
==Step 1: Plot points==
 
==Step 1: Plot points==
  
−
[[file:predicting-reservoir-system-quality-and-performance_fig9-36.png|left|thumb|300px|{{figure number|1}}Plot points of matching porosity and true resistivity (R<sub>t</sub>) values obtained from well logs on 2×4 cycle log-log paper.]]
+
[[file:predicting-reservoir-system-quality-and-performance_fig9-36.png|thumb|300px|{{figure number|1}}Plot points of matching porosity and true resistivity (R<sub>t</sub>) values obtained from well logs on 2×4 cycle log-log paper.]]
  
 
Plot points of matching porosity and true resistivity (R<sub>t</sub>) values obtained from well logs on 2×4 cycle log-log paper, as shown in [[:file:predicting-reservoir-system-quality-and-performance_fig9-36.png|Figure 1]]. Use the x-axis for the resistivity (R<sub>t</sub>) scale and the y-axis for the porosity (Φ) scale.
 
Plot points of matching porosity and true resistivity (R<sub>t</sub>) values obtained from well logs on 2×4 cycle log-log paper, as shown in [[:file:predicting-reservoir-system-quality-and-performance_fig9-36.png|Figure 1]]. Use the x-axis for the resistivity (R<sub>t</sub>) scale and the y-axis for the porosity (Φ) scale.
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==Step 2: plot r<sub>w</sub> point==
 
==Step 2: plot r<sub>w</sub> point==
  
−
[[file:predicting-reservoir-system-quality-and-performance_fig9-37.png|thumb|{{figure number|2}}Plot the R<sub>w</sub> value (resistivity of formation water) by plotting the R<sub>w</sub> point along the R<sub>t</sub> scale on the x-axis at the top of the graph grid where porosity is 100%.]]
+
[[file:predicting-reservoir-system-quality-and-performance_fig9-37.png|300px|thumb|{{figure number|2}}Plot the R<sub>w</sub> value (resistivity of formation water) by plotting the R<sub>w</sub> point along the R<sub>t</sub> scale on the x-axis at the top of the graph grid where porosity is 100%.]]
  
 
Plot the R<sub>w</sub> value (resistivity of formation water) by plotting the R<sub>w</sub> point along the R<sub>t</sub> scale on the x-axis at the top of the graph grid where porosity is 100%, as shown in [[:file:predicting-reservoir-system-quality-and-performance_fig9-37.png|Figure 2]]. R<sub>w</sub> values are published by logging companies, or we can calculate them from the SP log.
 
Plot the R<sub>w</sub> value (resistivity of formation water) by plotting the R<sub>w</sub> point along the R<sub>t</sub> scale on the x-axis at the top of the graph grid where porosity is 100%, as shown in [[:file:predicting-reservoir-system-quality-and-performance_fig9-37.png|Figure 2]]. R<sub>w</sub> values are published by logging companies, or we can calculate them from the SP log.
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{| class = "wikitable"
 
{| class = "wikitable"
 
|-
 
|-
−
! Porosity type
+
! Porosity type || Value for m
−
! Value for m
 
 
|-
 
|-
−
| Sandstones with diagenetic or detrital clay in pores
+
| Sandstones with diagenetic or detrital clay in pores || 1.7–1.8
−
| 1.7–1.8
 
 
|-
 
|-
−
| Formations with clean, macro- to micro-sized pore throats (Archie rocks)
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| Formations with clean, macro- to micro-sized pore throats (Archie rocks) || 2
−
| 2
 
 
|-
 
|-
−
| Formations with vuggy porosity (touching to nontouching)
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| Formations with vuggy porosity (touching to non touching) || 2.2–3.0
−
| 2.2–3.0
 
 
|}
 
|}
  
 
==Step 4: Plot the 100% S<sub>w</sub> line==
 
==Step 4: Plot the 100% S<sub>w</sub> line==
  
−
[[file:predicting-reservoir-system-quality-and-performance_fig9-38.png|thumb|{{figure number|3}}How to plot an ''m'' of 2.]]
+
[[file:predicting-reservoir-system-quality-and-performance_fig9-38.png|300px|thumb|{{figure number|3}}How to plot an ''m'' of 2.]]
  
 
On a Pickett plot, the value of ''m'' determines the slope of the S<sub>w</sub> lines. The first S<sub>w</sub> line plotted on a Pickett plot is the 100% S<sub>w</sub> line. To plot this line, draw a line with a negative slope equal to ''m'' that begins at the R<sub>w</sub> point. Use a linear scale to measure the slope; for example, go down [[length::1 in.]] and over 2 in.
 
On a Pickett plot, the value of ''m'' determines the slope of the S<sub>w</sub> lines. The first S<sub>w</sub> line plotted on a Pickett plot is the 100% S<sub>w</sub> line. To plot this line, draw a line with a negative slope equal to ''m'' that begins at the R<sub>w</sub> point. Use a linear scale to measure the slope; for example, go down [[length::1 in.]] and over 2 in.
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==Step 5: plot s<sub>w</sub> lines==
 
==Step 5: plot s<sub>w</sub> lines==
  
−
[[file:predicting-reservoir-system-quality-and-performance_fig9-39.png|thumb|{{figure number|4}}An example of plotting the lower percentages of S<sub>w</sub>.]]
+
[[file:predicting-reservoir-system-quality-and-performance_fig9-39.png|300px|thumb|{{figure number|4}}An example of plotting the lower percentages of S<sub>w</sub>.]]
  
−
After plotting the 100% S<sub>w</sub> line, plot the lines representing lower percentages of S<sub>w</sub> using this procedure.
+
After plotting the 100% S<sub>w</sub> line, plot the lines representing lower percentages of S<sub>w</sub> using this procedure:
  
−
{| class = "wikitable"
+
# Find the intercept of R<sub>t</sub> = 1 and the 100% S<sub>w</sub> line (made in the last procedure).
−
|-
+
# From this intercept, draw a line parallel to the x-axis across the plot. Any point on this line has the same porosity.
−
! Step
+
# Where this line passes through R<sub>t</sub> of 2, 4, 6, 8, 14, and 20, draw a series of lines parallel to the 100% S<sub>w</sub> line.
−
! Action
+
# Points on these lines correspond to S<sub>w</sub> of 71, 50, 41, 35, 27, and 22%. These percentages are calculated from the Archie equation using ''m'' = 2 and ''n'' = 2 at R<sub>t</sub> of 2, 4, 6, 8, 14, and 20.
−
|-
 
−
| 1
 
−
| Find the intercept of R<sub>t</sub> = 1 and the 100% S<sub>w</sub> line (made in the last procedure).
 
−
|-
 
−
| 2
 
−
| From this intercept, draw a line parallel to the x-axis across the plot. Any point on this line has the same porosity.
 
−
|-
 
−
| 3
 
−
| Where this line passes through R<sub>t</sub> of 2, 4, 6, 8, 14, and 20, draw a series of lines parallel to the 100% S<sub>w</sub> line.
 
−
|-
 
−
| 4
 
−
| Points on these lines correspond to S<sub>w</sub> of 71, 50, 41, 35, 27, and 22%. These percentages are calculated from the Archie equation using ''m'' = 2 and ''n'' = 2 at R<sub>t</sub> of 2, 4, 6, 8, 14, and 20.
 
−
|}
 
  
 
[[:file:predicting-reservoir-system-quality-and-performance_fig9-39.png|Figure 4]] is an example of following this procedure.
 
[[:file:predicting-reservoir-system-quality-and-performance_fig9-39.png|Figure 4]] is an example of following this procedure.
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[[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]]

Latest revision as of 16:16, 5 April 2022

A Pickett plot lets us compare water saturations of different parts of a reservoir in one or many wells. The Pickett plot[1] is a visual representation of the Archie equation[2] and therefore is a powerful graphic technique for estimating Sw ranges within a reservoir. All that is needed to make a Pickett plot is a set of porosities and corresponding resistivities taken from well logs and 2×4 cycle log-log paper. The procedure for making a Pickett plot consists of five steps, detailed below.

  1. Plot points of matching porosity and true resistivity (Rt ) on log-log paper.
  2. Plot Rw point on the Rt scale.
  3. Determine m using the table of values.
  4. Plot the 100% Sw line.
  5. Plot the lines representing lower values of Sw .

Step 1: Plot points

 
Figure 1 Plot points of matching porosity and true resistivity (Rt) values obtained from well logs on 2×4 cycle log-log paper.

Plot points of matching porosity and true resistivity (Rt) values obtained from well logs on 2×4 cycle log-log paper, as shown in Figure 1. Use the x-axis for the resistivity (Rt) scale and the y-axis for the porosity (Φ) scale.

Step 2: plot rw point

 
Figure 2 Plot the Rw value (resistivity of formation water) by plotting the Rw point along the Rt scale on the x-axis at the top of the graph grid where porosity is 100%.

Plot the Rw value (resistivity of formation water) by plotting the Rw point along the Rt scale on the x-axis at the top of the graph grid where porosity is 100%, as shown in Figure 2. Rw values are published by logging companies, or we can calculate them from the SP log.

Step 3: Determine m

Estimate m (cementation factor) using the table below. Laboratory analysis is necessary for a precise determination of m. However, by knowing what the expected porosity type is, we can estimate the value. If you are unsure of the porosity type, use an m of 2.

Porosity type Value for m
Sandstones with diagenetic or detrital clay in pores 1.7–1.8
Formations with clean, macro- to micro-sized pore throats (Archie rocks) 2
Formations with vuggy porosity (touching to non touching) 2.2–3.0

Step 4: Plot the 100% Sw line

 
Figure 3 How to plot an m of 2.

On a Pickett plot, the value of m determines the slope of the Sw lines. The first Sw line plotted on a Pickett plot is the 100% Sw line. To plot this line, draw a line with a negative slope equal to m that begins at the Rw point. Use a linear scale to measure the slope; for example, go down length::1 in. and over 2 in.

Figure 3 shows how to plot an m of 2.

Step 5: plot sw lines

 
Figure 4 An example of plotting the lower percentages of Sw.

After plotting the 100% Sw line, plot the lines representing lower percentages of Sw using this procedure:

  1. Find the intercept of Rt = 1 and the 100% Sw line (made in the last procedure).
  2. From this intercept, draw a line parallel to the x-axis across the plot. Any point on this line has the same porosity.
  3. Where this line passes through Rt of 2, 4, 6, 8, 14, and 20, draw a series of lines parallel to the 100% Sw line.
  4. Points on these lines correspond to Sw of 71, 50, 41, 35, 27, and 22%. These percentages are calculated from the Archie equation using m = 2 and n = 2 at Rt of 2, 4, 6, 8, 14, and 20.

Figure 4 is an example of following this procedure.

See also

References

  1. ↑ Pickett, G., R., 1973, Pattern recognition as a means of formation evaluation: The Log Analyst, vol. 14, no. 4, p. 3–11.
  2. ↑ Archie, G. E., 1942, The electrical resistivity log as an aid in determining some reservoir characteristics: Petroleum Transactions of AIME 146: 54–62.

External links

find literature about
Pickett plot construction 		       
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