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Line 14: − + − {| class = "wikitable"+ − |-+ − ! Step+ − ! Action+ − |-+ − | 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> . − |} − + Line 45:
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Line 39: − + − ! Value for m − + − − + − − + − − + Line 76:
Line 57: − 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"+ − + − ! Step+ − ! Action − − − | 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. − |} − The figure below is an example of following this procedure.+ + + + − + − + Line 116:
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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 = 9-60
| topg = 9-156
| 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
| isbn = 0-89181-602-X
| isbn = 0-89181-602-X
}}
}}
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 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.
# 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.
# Determine ''m'' using the table of values.
# Plot the 100% S<sub>w</sub> line.
# 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|{{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.
==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.
{| class = "wikitable"
{| class = "wikitable"
|-
|-
! Porosity type
! Porosity type || 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)
| Formations with clean, macro- to micro-sized pore throats (Archie rocks) || 2
| 2
|-
|-
| Formations with vuggy porosity (touching to nontouching)
| 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.
==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|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:
|-
| 1
# 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.
# 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.
# 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|thumb|{{figure number|9-39}}See text for explanation.]]
[[:file:predicting-reservoir-system-quality-and-performance_fig9-39.png|Figure 4]] is an example of following this procedure.
==See also==
==See also==
* [[Determining water saturation]]
* [[Determining water saturation]]
* [[Calculating Sw from the Archie equation]]
* [[Archie equation]]
* [[Determining Rt]]
* [[Determining Rt]]
* [[Calculating Rw from SP logs]]
* [[Calculating Rw from SP logs]]
[[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]]