The latest upgrade to the HMG Strata Log Software allows the user to toggle between a Measured Depth version (MD
Mode) of the log, and a True Vertical Depth (TVD)-corrected version (TVD Mode) of the log.
Moreover, when in TVD mode, the geologist can compare the TVD-corrected Log to up to three offset logs or any type of
TVD Log (TVD/Offset), on the computer screen (see above image). Use the F8 key or menu item: Mode->Toggle MD/TVD
Mode, to toggle between MD and TVD logs.
The above image shows an example of a log in TVD Mode. The area with the white background is the MD log converted to a TVD log. The graphs with the yellow and green background are TVD offset logs loaded into the software and correlated to the TVD-corrected log. A third TVD/Offset log (rose background) is not shown. When a measured depth log is converted to a TVD-corrected log, the log footage will be reduced. This is especially true as the borehole approaches horizontal as in the above example. For this reason, the software will automatically remove all text in the descriptions blocks that are greater than one inch in the Y-axis. In that way, sample descriptions will be removed, while

formation tops will remain, as shown in the above image. Also, the user can use the F10 key to remove all text elements in the graphs, making it easier to view the graph curves so important for correlation.
Entering Survey Data
Before a TVD-corrected log can be created, the survey information must first be entered into the program. The software will then use the survey data to adjust all curves, images, tops and texts to their respective True vertical depth (TVD).
Survey data is entered in exactly the same manner as in the Horizontal XSection program (for more information on surveys, follow this link: http://www.horizontalmudlog.com/pdfs/Chapter%205%20-%20Survey%20Data.pdf
).
The user can access the survey editor from the Tools menu, or by clicking on the Survey Editor Button as shown below.
Understanding TVD-Corrected Logs and Possible Pitfalls
The software uses the survey data to interpolate a TVD equivalent depth for every measured depth. However, since survey tools are sometimes 30’ – 90’ behind the bit, there is often data (for example gamma data – it is common now to have a near-bit gamma tool) on the log that is farther downhole than the last official survey. The software then uses the last survey inclination value to extrapolate the equivalent TVD depth for each MD beyond the last survey. This works well if there are limited doglegs between the last official survey and the bit, as might the case on a directional well.
However, if you are correlating the log in the middle of building the curve for landing a horizontal well, the inclination is probably increasing between the last official survey and the bit depth. In this case, for a more accurate TVD-corrected log, it is helpful to enter a projection to bit survey with the inclination increasing by an estimated dogleg amount.
How to use the Correlating Red Line
A simple procedure allows the software to draw a red line across all the logs to help with correlating stratigraphic position. This is done in TVD Mode by simply clicking (and holding down) the left-mouse key anywhere on the whitebackground TVD-corrected log. The red line will move up and down as the mouse is moved up and down the log.
Moreover, in the depth columns of the Mudlog and offset logs are displayed the TVD and the calculated subsea depth for each log. The example below shows the TVD and the Subsea of the red line for the TVD-corrected log. The three red circles in the first image (above) shows the location of the TVD and Subsea depths for the TVD-corrected log and two of the three TVD/Offset logs.

The TVD depth is drawn in black and above the red line, while the subsea depth is red and drawn below the red line.
Subsea depths are calculated from the inputted KB of the log and offset logs respectively. Hence, the correct KB elevation needs to be entered for the subsea value to be correct.
Locking the Scroll Bars
In TVD Mode, there are four separate scroll bars on the right side of the window, instead of the one in MD Mode. The scrollbar farthest to the right controls the white-background TVD-converted log. The other three scroll bars control each of the three offset Logs left to right respectively.
However, the software gives the user the ability to scroll the Mudlog and the offset logs together. This is done in two ways, by either using the Mudlog scrollbar with the shift key depressed, or by “locking” the offset scrollbars to the Mudlog scrollbar by depressing the F10 key. When the offset log scrollbars are locked to the main Mudlog scrollbar, a “Scrolls Locked” in parenthesis will appear in the mode status bar. Scrolling the main (farthest-right scrollbar) will move the TVD/Offset scrollbars in unison. Note: the opposite is not true, and scrolling the TVD/Offset logs will not move the main log scrollbar.
Even with the TVD Scrollbars Locked, the individual offset or TVD logs can be adjusted (scrolled) independently by their respective scrollbars and the Mudlog can be independently scrolled by using the mouse wheel instead of clicking on the right-most scrollbar.
The offset or TVD log tracks can only be edited when in TVD-Log mode.

There are two editing windows, one for the Log Data (the curves) that operates in similar manner as the regular graph editor. See the Horizontal XSection manual for more or follow this link: http://www.horizontalmudlog.com/pdfs/Chapter%204%20-%20Graph%20Data.pdf
.
The one difference between the TVD Graphs in TVD Log mode and the Graphs in the regular mudlog, is that you cannot enable semi-log graphs (though this will change in future updates). The “Set Start/End/KB Depths” menu (see above), opens up a simple window that allows the user to edit these depths accordingly. The KB of the offset log must be set for the program to accurately display the subsea depth for correlation purposes. If you plan on using the scrolls lock feature, it is a good idea to make the TVD/Offset log start and end depths the same as the mudlog itself. The reason is that when the scrollbar is locked, the TVD logs will scroll in lock step with the main log when the log scrollbar is moved
(except when using the mouse wheel). However, if the start or end of the TVD log is reached before the start or end of the mudlog, the TVD log will stop scrolling with the mudlog.
Only the TVD/Offset logs can be edited when in TVD mode; and there are only two editing modes available: Text Mode and Highlight mode.
The Text Mode works exactly as text mode on the MD log proper. Highlight mode is unique to the TVD/Offset log graphs and allows the user to highlight in transparent orange, any portion of the TVD/Offset logs. Simply hold the left-mouse button and move the pointer down log.
Note: the user can only highlight downward (increasing
MD).
The example to the left shows the user highlighting a high resistivity section (yellow curve) from 2866’ – 2906’.