elog guide

7/31/2019 Elog Guide

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GEOVIEW & eLOG Guide

Introduction to GEOVIEW............................................................................................................1

Part 1: Starting GEOVIEW.........................................................................................................2

Creating a GEOVIEW database.................................................................................................2Reading a well into GEOVIEW.................................................................................................4

Displaying a well in GEOVIEW..............................................................................................10

Creating a CGM File................................................................................................................22

Reading and Applying a Check Shot Correction.....................................................................24

Reading in a Second Well........................................................................................................35

Displaying the Wells................................................................................................................40

Part 2: Using the eLOG Program..............................................................................................42

Reading a Seismic File into eLOG ..........................................................................................52

Saving the Edited Logs ............................................................................................................72

The Crossplot Option in eLOG................................................................................................73


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Guide to GEOVIEW and eLOG

Introduction to GEOVIEW

GEOVIEWis a program that serves two purposes:

(1) GEOVIEWacts as a well-log database. All Hampson-Russell programs that use logsaccess them through the GEOVIEWdatabase. For this reason, GEOVIEWcontainsoptions for reading logs from ASCII files as well as directly from Landmark and

GeoFrame databases. GEOVIEWalso contains options for displaying logs andmaking synthetics, as well as applying checkshot corrections to logs. Finally,

GEOVIEWcontains options for editing and manipulating logs, through the eLOGprogram.

(2) GEOVIEWacts as a launch pad for other Hampson-Russell programs such asSTRATA and EMERGE. When these programs are launched from GEOVIEW, they

are automatically connected to the GEOVIEWdatabase, allowing them to access logs

directly. Sometimes the program buttons for Hampson-Russell programs may bedisabled or grayed out. This indicates that the computer on which GEOVIEWisrunning does not have a license for running that program. If you believe that your

GEOVIEWprogram buttons are incorrectly disabled, please contact the appropriateHampson-Russell office for support.

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Part 1: Starting GEOVIEW

The first step in running any Hampson-Russell program is to start GEOVIEW. On a Unix

system, this is done by going to a command window and typing:

geoview

On a PC, GEOVIEWis initialized by clicking on the Startbutton and selecting the Geoviewoption on the Programs / HRS applications menu.

If the GEOVIEWprogram does not start in either of these two cases, it means that there has beenan error in the program installation. Please contact your nearest Hampson-Russell office for

support.

Creating a GEOVIEW database

When you first launch GEOVIEW, the first window that you see is the Opened Database List,

which displays your most recently used databases. We will start by creating a new database. To

do that, click on New:

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Click on OK, and a menu appears, allowing you to enter the name of the new database. Use the

field at the top of this menu to select a location for the new database and call the new database

geoview_guide as shown below:

When you have filled in the new database name as shown, click on OK.

The GEOVIEWwindow now shows the name of the new database:

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Reading a well into GEOVIEW

Now we are ready to enter logs into the GEOVIEWdatabase. We will enter two wells in thedatabase. The first well is in the LAS format and contains a series of logs. The second well is in

a general ASCII format and we will use this well to correlate with a 3D seismic volume.

When the new database was created, an empty Well Explorerwindow appeared:

To enter the first well, click on Import Data / Logs, Check Shots, Tops, Deviated Geometry

from Files:

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This menu appears:

We must select the file(s) containing the log curves that we want to add to our database. Select

avo_well.las, as shown, and confirm that the File Formatis set toLAS:

Next, we need to specify the name of the well(s) into which we will load the logs. After youclick on Next >>, the second page appears:

The default name for theDestination Well

is acceptable, so click onNext >>

to see thesubsequent page:

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If values for the X & Y coordinates of the surface location of the well or the KB and surface

elevations had been found in the header of the LAS file, they would have been entered on this

menu automatically. You can also specify them yourself by modifying the contents of the

corresponding cell. For this well, we need to change only the Typeto GAS WELL, as shown:

Click on Next >>to proceed.

This causes the file to be read and the following table to appear:

This menu shows that GEOVIEWhas identified 5 logs in the file. To see the file itself, click onView File. A text window appears, allowing you to browse the LAS file.

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Under the heading Log Type, we see that GEOVIEWhas correctly identified each of the 5 logs:

Sometimes, a log cannot be identified correctly. In that case, either an incorrect type or the type

Unknown may appear. To correct that, click on the log type to be changed and a pullDown menu

allows you to set the correct Log Type:

Similarly, the Amp. Units may be modified if there were any errors in the measurement units

identified in the file header lines:

The column entitled Unique Log Name shows the names that GEOVIEWwill give to these logs:

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Finally, the column entitled Usage indicates whether you wish to actually read this log into

GEOVIEW:

If, for example, you did not wish to load the third log, (Gamma Ray), you could simply uncheck

the box on the third line, as shown:

For this tutorial, we wish to read all the logs listed, so click on Ok.

A dialog now appears confirming that the logs have been imported. Click on OKto finish

loading logs.

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The GEOVIEW Well Explorerwindow now displays information about the inserted well:

In the Viewpanel, the log has a vertical line through the blue box, indicating that this is a

vertical well.

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Displaying a well in GEOVIEW

Now we wish to display the well that has been entered. To do this, highlight the well name in

the Table Viewor Viewpanels, and then clickDisplay Well. This display appears:

You can see that a series of logs have been read in. If you move the horizontal scroll bar, all of

the logs can be seen. To modify the view parameters, click on View / Display Options.

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This menu appears:

This menu contains a series of tabs whose pages control the appearance of the log display. To

get an understanding of this menu, we will modify a few of the parameters. First, click on the

items Wavelets and Zero-Offset Synthetics:

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Then click on Apply at the bottom of the menu. The log display now contains those items:

Note that the zero-offset synthetics are created with the P-wave and density logs that are marked

with an asterisk (to indicate that they are the active logs).

To change the order of the displayed logs, click on the Item Display Order button:

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You will now see this menu, which sets the order in which display elements will be plotted:

Lets move P-wave after Gamma Ray. To do that, highlight Track 5(*P-wave) and click the Up

Arrow twice. The menu will now look like this:

ClickOK on this menu.

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Click on Apply on the Parametermenu to get the new display:

Note that by default, the primary vertical scale is actually in depth, rather than in time. To

change this, click on the Scale & Details tab and modify the page as follows:

Note that we have changed the Uniform Scale and Vertical Range items. Once again, click on

Apply:

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You may have to adjust the vertical scroll bar to see the lower portion of the logs as shown

above. This is because the vertical scale has now been set to 7.5 inches per second. As a final

change for this page, modify the scale parameters for the P-wave log: Plot Amp. Unitsto m/s,

Start Plot Amp.to 1500, and End Plot Amp.to 4000 as shown here:

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Click on Apply to get the new display:

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Finally, click on the Synthetics tab:

This page controls the wavelets that are being used to create the zero-offset synthetics. Right

now, there is only a single wavelet, the default wavelet wave0.

To see what this wavelet looks like, click on Wavelet Options / Display Current Wavelet:

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The wavelet display appears:

You can see properties of the wavelet, such as the amplitude and phase spectra, by selecting the

Frequency and History tabs of this display.

Now lets create some new wavelets to use for synthetics. To add a new Ricker wavelet, click

on Wavelet Options / Create Ricker Wavelet:

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This menu appears:

Lets modify the Dominant Frequency and Phase Rotation as shown here:

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Now, click on Create wavelet. The new wavelet name appears on the Available Wavelets listof the Parameter menu. By default, the new wavelet now replaces the previous wavelet as the

Displayed Wavelet. To see both synthetics at the same time, click on Add All >>. The menu

now looks like this:

Now click on Apply at the bottom of the menu. The new synthetics appear:

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Finally, modify the parameters at the bottom of the menu as shown here:

When you click on Apply, the display now looks like this:

Now that we have finished modifying the display parameters, click on Ok at the bottom of the

Parameter menu.

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Creating a CGM File

To create a CGM Hardcopy of the log display, click on File / Hardcopy / CGM File:

This menu appears, allowing you to control the appearance of the CGM file that will be created:

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To preview the CGM file, click on Preview:

The CGM Viewer shows the CGM file which has been created in the specified directory. You

can modify various parameters for that file. An important item is to click on the Title Block tab

and type in a description to be used on the CGM Title Block:

To conclude this section of the guide, click on Cancel at the bottom of the CGM File

Generation menu.

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Reading and Applying a Check Shot Correction

In this section, we will read in a check shot survey from an ASCII file.

First, go to the GEOVIEW Well Explorer window and click on Import Data / Logs, Check

Shots, Tops, Deviated Geometry from Files:

On the File Import page, select the file avo_check_shot.txtand click on Next >>:

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The ASCII File Format pageappears, allowing you to describe the format of this file:

To help determine the parameters, click on View File to see what the file looks like:

As you can see, there are two columns of numbers, containing the depths and the desired times.

In addition, there are 3 header lines to skip.

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Change the ASCII File Format pageas shown, and also ensure that the depths are read fromcolumn 1.

ClickNext >> on the ASCII File Formatpage.

Choose AVO_WELL as the destination well to place the check shot log into.

ClickNext >>on this page and the following page, until you see the Log File Details page:

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Fill in the menu as shown below. ClickOkwhen you have completed the menu.

After the check shot file is read, it will appear on the log list that can be shown by clicking on the

arrow beside the well name in the Table View. It also can be seen in the Log Display window.

At this point, we have read in the check shot file, but have not yet applied the correction to the

logs inAVO_WELL. To do this, go to the Log Displaywindow and click on Option / Check

Shot Correction:

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Two windows now appear. One window shows the result of applying the check shot correction

to the sonic log:

As you can see, the point at 300 m depth causes quite a distortion of the resulting sonic log.

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The other window is a menu containing the parameters for the check shot correction:

Lets modify some of the parameters to see the effect. First change the Type of Interpolation to

Linear:

Then click on Apply to see the new check shot correction:

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Note that the changes to the sonic log are quite drastic.

Now change the Type of Interpolation to Polynomial, set the Polynomial Order to 3, and check

the toggle to Apply a Smootheras shown:

When you clickApply, the effect on the sonic log is greatly reduced, but this is because the

check shot points have not been honored exactly:

Finally, lets assume that we wish to edit the second check shot pair. First go back to the

parameter menu and reset the Type of Interpolation to Spline and do not apply a smoother, then

clickApply.

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Once again, the corrected sonic log looks like this:

Now use the mouse to draw a box around the second check shot point in the Drift Curve:

Then click on Edit / Delete Point:

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The second point is then removed and the corrected sonic log now looks like this:

Finally, lets investigate the Sonic Log Changes parameter on the Check Shot Parameters

menu:

This parameter controls the changes (if any) that will be made to the sonic log velocities. There

are three options:

The default is Apply relative changes. This means that the sonic log will be modified only for

depths between the first and last check shot point. This is the one that we have been using up to

now.

The second option is Apply all changes:

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If you choose this option and click on Apply, you will see that a series of velocity values have

been inserted above the first logged point. These values have been calculated to precisely cause

the exact check shot times to result if the calculated log is converted from depth to time:

This option would be useful if you wanted to export the check shot corrected sonic log to another

system.

The third option is Change depth-time curve only. Selecting this option means that the depth-

time curve will be modified, but the sonic log amplitudes will be left entirely as before:

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Lets assume that the default selection for Sonic Log Changes is an acceptable correction. Set

this back to the default, as shown, and clickApply:

To save the resulting log, click on Ok on the Check Shot Analysis window. This menu

appears, indicating that a new sonic log will be created with the name P-wave_chk.

ClickOk on this menu.

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You will see the new sonic log in the Log Display window:

Reading in a Second Well

Now we will read in a second well log in general ASCII format. To start that, click on Import

Data / Logs, Check Shots, Tops, Deviated Geometry from Files:

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On the File Import page, select the file strata_well.txt:

After you clickNext >>, this page appears:

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In order to fill in this menu, we need to see the input file, so click on View File. This display

appears:

Note that the sonic log is listed in two columns, the first containing the depths and the second

containing the transit-times. Also, there are 11 header lines to skip (including the blank line).

This means that the first parameter we need to change on the ASCII File Format menuis theNumber of header lines to skip. Also, change the Input Sampling Units to Feet.

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Change these values as shown above, and click on Next >>.

On the Destination Well Settingspage, change the name of the Destination Wellto strata_well

by clicking in the cell and typing in the new name.

ClickNext >>to display the following page. From the selection list under Type, change this

well type to GAS WELLas shown.

ClickNext >>to display this page.

Since this file only contains a single P-wave log, fill in the menu appropriately (simply change

the Log Typeto P-wave and accept the default values).

ClickOk when you are finished to read in the new log and dismiss the menu.

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The GEOVIEWWell Explorer now shows the new well:

If you clickDisplay Wellafter highlighting strata_well, you will see the sonic log which has just

been read in:

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Displaying the Wells

In the GEOVIEWWell Explorerwindow, you can navigate between the well, log and top anddeviated geometry levels. The Viewpanel shows it as a tree style display:

Then, using the arrows, the data are shown, as below:

The list appears showing all wells entered into this database as above.

Clicking the arrow by the name strata_well gives the list below, showing you all the logs entered

for this well:

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Note that the log calledDepth-time_P-wave_1 is the depth-time curve calculated for the sonic

log. Note also that any of the parameters may be modified on this menu. For example, suppose

that the units for the P-wave log had been incorrectly entered. To modify the value, click on the

field containing the value us/ftand a pullDown menu appears allowing you to change the units:

From this menu, the Tops and Deviated Geometry (if applicable) can be viewed.

From the Log Display List, you may also see the actual log data samples. To do this, click on

the arrow button beside the name P-wave_1:

You can see all the sonic log sample values by moving the vertical scroll bar. Values in this

table can be changed manually.

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Part 2: Using the eLOG Program

The eLOG program is used to perform manipulations on the logs such as editing, smoothing, and

log correlation. In this section of the guide, we will use eLOG to modify some of the logs that

have already been entered into the database.

To start eLOG, click on the eLog button on the GEOVIEWmain window. A menu appears,allowing you to start a new project. Click on Ok. On the file selection menu, call the new

project elog_guide as shown below:

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Click on OK, and the eLOG main window appears:

At the same time, a menu appears asking which well we wish to edit:

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On this menu, select strata_well and click on Ok.

The eLOG window will now contain the log from strata_well:

The eLOG window looks very much like the Log Displaywindow from GEOVIEW, with the

addition of a series of editing buttons down the left side.

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We will do a series of operations on the P-wave log from strata_well. The first thing we will do

is to apply a median filter to the log to remove the high-frequency noise. To do this, click on the

Math button. When this menu appears, select the Median Filter option, as shown:

The median filter is a math operation using one or more input logs, which will come from

strata_well:

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On the following page, click on Next >>to accept the defaults because we will write the median

filtered log back to the same well:

Now, select the log to median filter, which will be P-wave_1 from strata_well:

Call the output sonic log P-wave_math as shown, and click on Next >>.

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The menu now shows the parameters for this option. Change the Operator Length to 9, as

shown, and click on OK.

When the process has completed, the new filtered log appears:

By default, only the latest P-wave log appears in the eLOGwindow. In order to see both logs,

we need to temporarily modify the display parameters. To do that, click on the eyeball icon:

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On the Layout page of the Parameter menu, the important parameter is the option Display Only

Active Logs:

If there is more than one log of a particular type (for example, the P-wave logs in this well), one

of them is selected as having a higher priority. This is called the Active Log. By definition,

whenever a process is applied which creates a new log, such as check shot correction or median

filter, the latest log is automatically set to be the Active Log. To see the list of active logs and

possibly modify that list, click on the Active Logs button.

The resulting menu allows you to define the priority yourself:

We are happy with this priority, so cancel this menu.

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Since we want to see both of the P-wave logs (before and after median filter), we must allow

display of multiple curves by unchecking the Display Only Active Logstoggle:

Check the box for the P-wave_1 log as shown to display the original log adjacent to the median

filtered version:

Click on Apply at the bottom of the Parameter menuand both logs are displayed in the eLOGwindow.

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From this display, we can see that the median filter has removed much of the high-frequency

jitter from the sonic log. For the rest of the processes, we will be happy to see only one log, so

click on Cancel on the Parameter menuto reset the eLOG window.

The next process we will apply is to create a density log using Gardners equation. To do that,

click on Transforms and modify the first page as shown below (Select Gardners Equationunder the item Select desired operation):

Then click on Next >> and modify the second page to select strata_well:

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Click on Next >> to display the third page. The default selection causes the output log to be

written into strata_well:

After clicking on Next >>, the fourth page shows that P-wave_math will be used as the input log.

We will change the default name for the output Density log to Density_gardner:

Then click on Next >> to see the transform which will be applied:

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Finally, click on OK and the density log will be created:

Reading a Seismic File into eLOG

Now we will perform the operations of wavelet extraction and log correlation. To do this, we

must first read an external seismic volume.

To start this process, click on Data Manager / Import Data / Open Seismic / From SEG-Y File:

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On the File Selection page, select the file ersk3d.sgy, which will be found in the elog_data

directory.

Click on Next >> to get the next page.

The file is a 3D seismic volume with a rectangular grid of inlines and cross lines. This page of

the menu defaults to a 3D volume:

After you click on Next >>, you see the third page, which asks about the information that is

available in the trace headers:

Note that eLOG is capable of reading the Inline & Xline numbers and/or the X & Y coordinates

from the trace headers, but since neither of these is present, we will load the seismic by keying

on the CDP number. In order for this to work, the seismic data must form a uniform, rectangular

grid. For this file, this is the case.

After modifying the menu as shown above, click on Next >>.

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The SEG-Y Formatpage appears:

This page is where you specify various byte locations for parameters from the trace headers. The

default values are the standard SEGY locations. Because we have specified that the geometry is

Rectangular, the only important locations for this data set are the CDP and Offset locations, as

shown above. Click on Next >> on this menu.

If you have never read the file ersk3d.sgy before, you will see the following message:

This is because eLOG must scan the file to determine general information from the headers. If

you have read the file at least once before, you will not see this message. Click on Yes to

continue.

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The final menu appears:

Because we have specified the geometry as Rectangular, we must now specify the Geometry

layout. For this purpose, we simply need to tell the program that there are 155 Cross-lines. Thenumber of Inlines will then be calculated automatically. The menu will now look like this:

Since we will be using this data set only for log correlation and wavelet extraction, we will not

bother to fill in detailed X & Y coordinate information. Click on Ok on this menu.

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When the file has been read, two new windows appear. One window contains the seismic data:

The second window contains this list of the wells in the database, and their location within theseismic grid:

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At this point, the Inline and Xline numbers at which the wells have been positioned are not

correct. In order to do that, we would have to specify the correct X & Y locations of the wells in

the GEOVIEWdatabase as well as the correct X & Y geometry of the seismic grid. Since wewill be correlating strata_well, we only need to specify the position of that well correctly.

AVO_WELL does not tie this data set. The strata_well is located at Inline 24 and Xline 75.

Type those numbers in, click in another field, and the menu will be updated to look like this:

Click on Ok.

The Seismic datawindow now shows a portion of Inline 1. To look at the data near the well,

type the number 24 in the Inlinebox at the top and clickEnter:

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After moving the scroll bars, you can see the sonic log from strata_well positioned properly

within the volume:

The seismic data window has many useful viewing capabilities. For now, we will return to the

eLOG main window, to continue with the log editing session.

Now that we have loaded the seismic data, we will proceed with Log Correlation. Click on the

Correlate button:

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This menu appears:

Log correlation is the process of aligning the synthetic calculated from the well logs with one ormore seismic traces near the well location. In eLOG this correlation is always done with a

"Composite Trace. The Composite Trace is an average of adjacent traces around the borehole

location. If the well is deviated, the averaging follows the deviation path. The menu above

determines how the averaging will be done. By selecting the default parameters, we are

averaging traces within +/- 1 inline and crossline of the borehole in other words, 9 traces.

Click on Ok to accept this default.

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The eLOG main window now looks like this:

Log correlation can be thought of as a type of check shot correction, where the depth-time pairs

are provided manually by selecting points on the synthetic and tying them with correspondingpoints on the composite trace. The trace shown in blue is the synthetic trace calculated with the

most recently defined wavelet. To see that wavelet, click on Wavelet / Display Current

Wavelet.

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We see that it looks like this:

A better wavelet would be one that was extracted from the seismic data. To do this, click on

Wavelet / Extract Wavelet. We see that there are two options:

These are Use Well and Statistical. In order to get the correct phase of the wavelet, wewould prefer to use the well. Because we have not done log correlation yet, the mis-tie between

log and seismic would make that extracted wavelet unacceptable. For this reason, we start by

extracting a statistical wavelet, which will be a zero-phase wavelet with the same amplitude

spectrum as the seismic data.

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Select Wavelet / Extract Wavelet / Statistical:

In the menu shown above, we have selected a time window of700 to 1200 ms and limited theanalysis to a range of traces around the well.

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Click on Next >> twice to get the last page:

In this case, we will accept the default values. Click on OK to get the extracted wavelet:

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The eLOG main window has now been redrawn to contain a synthetic created from this extracted

wavelet. We can see that the character tie has improved significantly:

Obviously, there is a time shift between the blue synthetic trace and the red composite trace.

The first step is to correct this shift. Click near the peak on the synthetic at about 750 ms and the

corresponding peak on the composite trace:

Then click on Stretch at the bottom of the window.

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The synthetic has been aligned using the picked values:

The calculated correlation coefficient at the bottom of the window measures the fit

mathematically:

Obviously, the fit is still not good enough, and this is because there is a time-variant stretch

required. The next step is to pick a series of points:

Click on Stretch.

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This time the check shot windows appear:

Whenever there is more than one point in the correlation picks, this is interpreted as a type of

check shot, and these windows appear.

To accept this correlation, click on Ok on the Check Shot Analysiswindow.

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The synthetic trace now shows a much-improved correlation:

with a correspondingly larger numerical correlation value:

Now that the log has been correlated better, we can extract a new wavelet using the log. Click

on Wavelet / Extract Wavelet / Use Well:

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On the first menu, select strata_well as the one to use for wavelet extraction:

Click on Next >>.

On the next page, set the time window from 700 to 1200 ms:

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Click on Next >> twice. On each subsequent page, accept all the defaults.

Click on Next>> to see the history which will be saved with this wavelet:

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Finally, click on OK to get the extracted wavelet:

Click on the Frequency tab on this window to see its frequency spectrum:

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The eLOG window shows an improved correlation with a larger numerical correlation of about

0.86:

Now that the correlation has been completed, click on Ok at the bottom of the eLOG window.

This menu appears, showing you the name of the name correlated sonic log:

Click on Ok on this menu to accept the suggested name.

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Saving the Edited Logs

We have now completed the editing of the well log. At this point, the changes are contained

only within the eLOG project. This means that the GEOVIEWmain window still contains onlythe original logs. We can still choose to discard these edits if we wish. To save both the eLOG

project and the edited logs, click on Project / Save. The following question appears:

We want these changes to be stored permanently in the GEOVIEW database, so the answer to

this is Yes. This list appears, showing all the new logs that have been created and the names

under which they will be saved:

Click on OK on this menu to save all the new logs. Go back to the Well Explorerwindow, andyou can see that the new logs P-wave_math, P-wave_corrandDensity_gardnerhave been

inserted into strata_well.

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The Crossplot Option in eLOG

We will now look at the Crossplot option in eLOG. To do this, we will first display

AVO_WELL from the database. To do this, click on Open Well to get the list as shown:

SelectAVO_WELL and click on Ok.

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This will loadAVO_WELL into the eLOG window. The resulting window looks like this:

Next, click on the Crossplot button on the sideBar to bring up the Well Log Crossplotmenu.

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Select from the list ofAvailable types and click on Add >>. Repeat these

steps to select P-wave,Density, Gamma Ray, SP, andResistivity so that the menu appears as

shown:

Note that will be selected automatically since the Processing domain type is

the Vertical Depth Domain.

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Click on Next >> to get the second page of the Well Log Crossplotmenu, which allows you tochoose the wells. Fill in this menu as shown below, to chooseAVO_WELL:

Click on Next >> to get the third page of the Well Log Crossplotmenu, which defines thecurves that will appear on the X and Y axes.

Modify the menu to plot the P-wave log on the X-axis and the Density log on the Y-axis. Thecompleted menu looks like this:

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Click on Next >> to get the next menu page, which allows you to choose among logs of the same

log type in addition to selecting the amplitude units.

Accept the defaults by clicking on Next >>.

The next page of the menu allows you to select the depth range for cross plotting. Fill in a Start

Depth of 550 m and End Depth of 700 m, as shown below:

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Click on Ok, and the following cross plot will appear, where Density, in g/cc, has been cross

plotted against P-wave travel time, in s/m:

The default color key shows Vertical Depth. If we wish, we can use one of the other logs to

create the color bar, creating a type of 3-dimensional plot. To do this, click on NewPlot /

P-wave vs Density (primary), to get the Data Specificationmenu.Fill in the menu as shown below, by changing Item # for Color to 6(notice that this is the

Column number of the Gamma Ray curve from the list in the top half of the menu):

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Click on Ok to get the same cross plot with a new color scheme.

Now, go back to the NewPlot / P-wave vs Density (primary) and change the color key back to

Vertical Depth by changing Item # for Color back to 5.

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Now, click on the Transform / P-wave vs Density (primary). Fill in the Transform Datamenu as shown below, by changing the Xand Yaxis values to Log(x) and Log(y):

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Click on the Ok button to bring up the transformed cross plot:

We will now perform a regression analysis on the transformed axes.

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Click on Regression / Least squares, to bring up the following menu:

Accept the defaults by clicking on Ok.

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The resulting cross plot has the linear regression line drawn on it, and the equation is shown in

the legend.

Next, click on Cross-Section to produce a display of the two log curves, P-wave and Density.

Use the View / Zoom button or the magnifying glass icon to zoom in on the curves:

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We next want to select certain zones on these curves from clusters on the cross plot. To do this,

click on Zones / Add to get the Add Zone menushown here:

The first color is a dull gray. To change this to a brighter color, like red, click once on the color

itself to bring up the color editor, shown next (the appearance of this menu will depend on

whether you are running the program on a PC or under Unix):

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On the color editor, click once on the red color (second down from the top left corner), and you

will see the Color/Solidbox change to red. Click on OK to save this color. Now, go back to the

cross plot itself. Following the instructions at the top of the Add Zone menu, draw an ellipse

around the points as shown. Click on Apply on the Add Zone menuto save zone1, as shownhere:

Note that your ellipse may be slightly different. Now, add a second ellipse on the set of points to

the right of the first ellipse. Click on Apply again to get something similar to the next plot:

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Now that the two ellipses have been drawn, look at the two well log traces again. Notice where

the elliptical zones are present on this plot, as shown below:

We will choose to keep only the points in the second zone. To do this, click on Filter / Filter

points, and fill out the menu as shown below, by choosing Remove Points Outside Zoneandaddingzone2 to the Selected List:

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Click on Ok to filter the points, and the result will look like this:

Now, recalculate the regression fit, using the Regression / Least squares option and clicking

Ok to choose the defaults. The new fit looks like this:

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What is the significance of the two linear regressions that we performed on the cross plotted

data? Note that the first was done on the overall dataset, and the fit did not appear to have a high

correlation value. The second was done on a more restricted set of points, and had a better

looking fit. Now, recall Gardners equation for the fit between density and velocity:

baV , = where = densityV = P-wave velocity

a, b = constant values

Although the above equation is nonlinear, we can linearize it by taking the logarithm:

log() = log(a) + b log(V)

Now you can see why we applied a logarithmic transform to each axis. However, we also used

transit-time rather than velocity units, where:

1,000,000V ,

t=

t transit-time in s/m =

or

log(V) = log(1,000,000) - log( t) = 6 - log( t)

Substituting gives us:

log() = log(a) + 6b b(log ( t) )

Let us write the least-squares fit from the cross plot as:

log() = c(log( t) ) + d

Note that your c and d values will probably not be the same as here, since your elliptical region

will be slightly different than the one shown. Equating the a and b values from Gardners

equation with the c and d values from the program, we get:

b = -c

a = 10^[d - 6b] = 10^[d + 6c]

The regression line on the cross plot above was as follows:

y = -0.444688x + 1.51878, where y = log()

and: x = log( )t

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So we have:

c = -0.444688, d = 1.51878

and therefore:

b = 0.444688

a = 10^[1.51878 2.66813] = 10^[-1.14935] = 0.0709

Thus, we can write Gardners equation as:

= 0.071 V0.445

To perform this transform, go back to the eLOG window containingAVO_WELL and click on

Transforms. Fill out the Transforms menuas shown below (i.e. apply Gardners Equation):

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Click on Next >>, and fill out the next menu as follows, by selecting AVO_WELL:

Click on Next >>, and fill out the menu as follows, selectingAVO_WELL as the Output Well:

Click on Next >>, and fill out that menu as follows, selecting P-wave_chkto be the InputP-wave log andDensity_Gardneras the Output Density log:

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Click on Next >> and fill out the final menu with the computed coefficients, 0.071 and 0.445, as

shown below:

Click on OK and the resulting density log will look like this:

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This is the end of the GEOVIEW/ eLOG tutorial. To close down the eLOGprogram, click onFile / Exit Project on that window.

You will be prompted to save your project. If you want to review the tutorial data later, click on

Yes:

elog guide

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