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HELP: PfEFFER-java |
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PfEFFER makes a Pickett plot using information drawn from the home area of a unit worksheet. The coordinates of the zones on the plots are set by values found in the RT and PHI columns. The position and orientation of the water saturation and bulk volume water (BVW) lines are controlled by the Archie equation parameters and formation water resistivity (RW) values recorded in the Archie parameters. The parameter values may either be known, estimated or guessed. A fundamental rationale for this program is to provide the means to resolve problems and to reduce uncertainty : solving by doing. This demonstration will continue with the Miss C flow unit.
Click on the 
icon image to display the Pickett Plot.
The program generates a crossplot of resistivity (RT) and porosity (PHI) values
recorded for the depth interval of the unit sheet. Notice that the plot also carries
the name of the well, the depth range of the unit and the Archie parameters values.
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Selection of the SW button on the Pickett Plot Annotation toolbar triggers the SW Lines dialog box. The check boxes allow the user to select a set of water saturation lines. In this example, we have elected to plot lines at 20, 30, 40, 50, 60, 80 ,100 percent values. The line for 100% water saturation is commonly called the "water line". Up to five other saturation values may be entered in the boxes provided, 25 and 35 percent is added. (Another useful feature is that if a line or lines need to be removed from a subsequent Pickett plot, this can be achieved by recalling the SW Lines dialog box using the SW button
The water saturation lines are located on the plot as dictated by the Archie parameter values. The intercept of the water line is located at A*RW on the total porosity axis (fractional porosity of value 1). The slope is the same for all water saturation lines and is controlled by the Archie cementation exponent, M. The spacing of the water saturation lines is a function of the Archie saturation exponent, N. The water saturation lines are colored blue and labeled with their SW values in percent. Remember that if the user wishes to eliminate lines or insert additional water saturation lines, this may be achieved by selecting the SW Lines dialog box (by pressing the SW button) and changing the line selection.
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We continue the demonstration with Miss C flow unit with the plotting of bulk volume water (BVW) lines.
Bulk volume water lines may be plotted on a Pickett plot by clicking the BVW button. The BVW LINES dialog box then appears with a check box format for the selection (or deselection) of BVW values recorded in fractional values. Notice that up to three additional BVW values may be typed in to match user- selected values. The user’s choice of values is usually dictated by considerations of the likely Buckles number that would discriminate productive zones in the unit analyzed. The Buckles number will reflect typical pore size in the reservoir rock and, to a lesser degree, the height in the hydrocarbon column. In this example, we have elected to plot BVW lines of 0.03, 035 abd 0.04 on the Miss C Limestone Pickett plot, following the broad rule-of-thumb that 0.04 is a useful production discriminator in carbonates.
Additional lines may be added and others removed on the Pickett plot through recall of the BVW lines dialog box by clicking the BVW button. This feature allows a relaxed analysis in which casual initial choices can be sharpened after visual inspection of the Pickett plot.
The bulk volume water (BVW) lines are plotted in red on the Pickett plot and
tagged as BVW with their associated values. In this example, the BVW lines are
vertical because the cementation exponent, M is equal to the saturation
exponent, N. Otherwise, the BVW lines would lean to the right if N>M, and
would lean to the left if N When the K button is selected, the user is presented with the
PERMEABILITY dialog box. As with the other dialog boxes, the choice is
arranged in a check box format, so that permeability values can be selected or
deselected. Notice that other permeability values can be typed into the slots
marked Other.
The permeability will be computed as a prediction keyed to porosity and
"irreducible" water saturation using the Wyllie-Rose relationship of:
k = P * ΦQ / SwiR
where P, Q, and R are constants, whose values from the Archie and Other Constants Panel on
the PfEFFER "Spreadsheet".
The PfEFFER default values for P, Q, and R are those of the Timur
equation which are appropriate for predicting permeability in typical
sandstones. The values are not appropriate for limestones and so substitute
values have been inserted in this example and are based on a highly generalized
relationship from carbonate reservoir data. In all cases, the onus lies with the
user to accept or substitute usable values for P, Q, and R.
The predicted permeability lines are drawn in green. Even if the equation
parameters are essentially correct, the predicted permeabilities will only be valid
when zones are at "irreducible" water saturation. Therefore, the user needs to
establish a trend of points that appears to represent a reservoir section or
propose an irreducible BVW value (Buckles number) based on reservoir rock
type. Zones along a reservoir trend can be concluded to be approximately at
"irreducible" water saturation and so their predicted permeabilities deduced
from interpolation between permeability contours.
All other zones represent either transition zones or water zones and
therefore are not at "irreducible" water saturation. However, their
permeabilities can be estimated by migrating each zone Pickett plot coordinate
location along its porosity line to the BVW line considered to represent
"irreducible" reservoir conditions, and then interpolating between permeability
contours.
The points on a Pickett plot may be color-coded according to the values of
depth column on the worksheet, provided that there are no missing
values in that column. Selecting the "Att" Button presents with the
User Input Dialog allowing you to select one of five colors to represent each
of five different intervals of data values:
The default interval limits represent five equal divisions of a range that is
slightly larger than the actual range of data values. You may change the limits
as you please. You may use fewer than five intervals by deleting the contents of
the appropriate interval limits edit boxes. The points on the Pickett plot will
then be colored according to the specified ranges of the selected data value and a
color key will be added in the lower right corner:
Select the "Print Graph" Button at the bottom of the Pickett Plot and the "Select
a Different Directory Path" Dialog will appear.
Enter a directory path or select
the "Search" Button and find the directory path. You can change the name of the
Pickett ".png" text field to any name you wish and select the "Continue" Button and
a the Pickett plot will appear as a Portable Document Format (PDF) document will
appear. The program also creates a Portable Network Graphics (PDF) image file with
the PDF Document in the same directory.
Adding Permeability Lines
Plotting Attribute Values On The Pickett Plot
Printing the Pickett Plot
Example: PNG File
