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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 |
− | | 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 |
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| | 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. |
| | | |
− | {| 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|{{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) | + | | 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. |
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| | | |
| ==Step 5: plot s<sub>w</sub> lines== | | ==Step 5: plot s<sub>w</sub> lines== |
− | 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"
| + | [[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>.]] |
− | |- | + | |
− | ! Step
| + | After plotting the 100% S<sub>w</sub> line, plot the lines representing lower percentages of S<sub>w</sub> using this procedure: |
− | ! Action
| |
− | |- | |
− | | 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.
| |
− | |}
| |
| | | |
− | The figure below is an example of following this procedure.
| + | # 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]] |
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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]] |