|Dual Induction Log|
Dual Induction Log correction
This routine (and the program for Dual Laterolog correction) use Asquith's equations. They deliver reasonable corrections to deep resistivity and are usually close to the values you get by hand off a 'tornado' chart for typical Rxo/Rm ratios.
I have found these equations reliable for very low to moderate resistivity water sands in the midcontinent USA, but be careful as to mud conditions. The assumption seems to be that Rxo/Rm ratios should be in the neighborhood of 20. For different ratios you should use the charts provided by logging companies. These equations also sometimes produce corrections to the deep resistivity greater than 100%...in which case you should just use the logged reading for the deep resistivity curve.
I admit that these corrections aren't very large, but there are oil plays where one ohm*meter of resistivity can make or break a good reservoir. If this kind of play is your cup of tea, by all means incorporate every correction possible. Be aware of invasion profiles, and look for the proper curve sequence (deep < medium < lateral resistivity). The medium curve is the cause of most problems because it has a significant borehole effect, often used to indicate fracturing in the reservoir.
Do you want to save your calculations? The input box at the very bottom of the screen records all the inputs and outputs for each calculation run. To save this information, select all the text in the box and copy it, then open a spreadsheet and paste it in as comma-separated values. Each data type will land in its own column, and each calculation run, or depth, will occupy a row. Format the spreadsheet to separate rows into different geologic formations, and you're done. Isn't that easier than writing everything down?
Don't have a spreadsheet handy? If you are working on a phone or a tablet, you can still copy the text and paste it into a note or an email.
The Recording box will reset if you press the "Help" or "Reset" buttons, or if you navigate to a different page.