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HELP: Hingle and Pickett Plots |
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PfEFFER Toolbar has a set of buttons designed to ease the transfer of data from the log input columns to the right into the home area columns RT, VSH and PHI. The Vsh button is placed before the Phi button because the VSH column may be employed in the computation of PHI and so the computation of VSH would logically come first. (However, it is possible to establish a formula involving the VSH column, even when it is empty.) We will demonstrate the use of these buttons using the Miss C worksheet in the wiz.las workbook, which we created from 12345a.las and 12345b.las.
Clicking on the RT button will launch the Rt Log Curve Selection dialog box, allowing you to select the input log to use as RT. In this case we are slecting ILD Deep Induction Resistivity, which was loaded into the column RT of the Miss C worksheet:
The VSH button is used to establish the formula for the VSH (shale proportion) column, based on any log curve, the user has to decide the clean formation value and the shale value of the log curve selected. Using the Gamma Ray as an example, we will continue using the Miss C worksheet in wiz.las to demonstrate the Vsh computation. To compute the Vsh from the Gamma Ray Log Curve.
The Vsh will be computed as
Vsh = (GR - GRc)/(GRsh-GRc)
where GR is the observed gamma ray value and GRc and GRsh are the specified gamma ray values for clean formation and for shale.
Select the Gamma Ray log curve which will then display the Vsh Data Limits Dialog to specify the gamma ray values for clean formation and shale ...
The Vsh Data Limits dialog box indicates the range of gamma ray values present on the worksheet, as a guide. After we click OK on this dialog box, the software will automatically compute the the VSH data and transfer the data to the Pickett and Hingle Plots.
Note that although the dialog boxes above refer to the gamma ray log, any log could have been selected, with the appropriate values for clean formation and shale being given in the Vsh Data Limits dialog box. The resulting formula simply refers to whichever column was selected in the second dialog box, gamma ray or otherwise. For example, we could have selected an SP log instead, entering SPc and SPsh into the Vsh Data Limits dialog box, rather than GRc and GRsh.
Clicking on the PHI button will launch the Log Selection dialog box, presenting you with four options for computing porosity ...
The four options correspond to the following formulas, with and without correction for shale volume,
| Without correction | With correction | |
| Density | (ρma - ρb) / (ρma - ρf) | [ρma - ρb - Vsh(ρma - ρsh)] / [ρma - ρf] |
| Neutron | Φn | Φn - Vsh * Φn sh |
| Density/Neutron | √[(Φn2 + Φd2) / 2)] | [Φn - (Φn sh / Φd sh) * Φd] / [1 - Φn sh/Φd sh] |
| Sonic | (Δtma - Δtb) / (Δtma - Δtf) | [Δtma - Δtb - Vsh * (Δtma - Δtsh)] / [Δtma - Δtf] |
In each case you will be requested to specify columns containing the appropriate logs and also to specify the constants in the selected equation (such as ρma and ρf). You will also be asked whether you want to correct for Vsh, as described below. Indicate your choice of logs by selecting the appropriate radio button on the Log Selection dialog box and then clicking OK. Here we have chosen to compute the porosity from a density log.
You are now presented with the Parameter Values dialog box ...
which lets you specify the parameters in the selected equation, in this case matrix (or grain) density and fluid density (ρma and ρf). Since the Miss C is a limestone interval, we have entered 2.71 for the grain density above. The default value for fluid density is 1.0, which we will leave unchanged.
We could choose to include a Vsh correction by clicking on the Correct for Vsh? check box. Doing so will activate the Shale Density (RHOsh) edit box, allowing us to enter the needed value. The shale correction is based on the values in the VSH column. (If you select the Vsh correction prior to filling the VSH column, the formula for PHI will still be set up correctly, but the resulting porosity values will be null. The porosity values will be set to their proper numeric values once values are entered for VSH.) For now we will choose not to use the Vsh correction. The Parameter Values dialog box is similar for the other three porosity computation options, although it contains only the Vsh Correction box for the neutron porosity and density/neutron porosity options. After clicking OK on the Parameter Values dialog box, the program will set up the formula for the PHI column and transfer the Total Porosity Data to the Hingle & Pickett Plots. Notice also that the Total Porosity Axis title is modified on the Control dialog as well as the both plots. The Porosity Constants will also be modified.
Note that the Pickett plot computations expect porosity as a fraction, not in percent. Using the density and sonic options to compute porosity will yield fractional values automatically. Hingle & Pickett Plots Applet automatically converts porosity logs that are Percent to fractional values when the LAS file is imported into the program.