About LogCalc

*How does the new data-logging feature work? Click to see an example.

Welcome to LogCalc

LogCalc gives petroleum geologists and engineers a slick, polished way to interpret open hole well logs. It will run on any device that has a web browser, and it looks sharp on tablets. You can even use it on your cell phone!

The program forms scroll up and down, resize to match your device, and flip if you turn your screen sideways. Program buttons are finger-sized.

Do you make off-the-cuff calculations on key zones, looking for bypassed oil? Are you still pounding the keys of an ancient HP or TI calculator? Try LogCalc: it will take you half the time to work through that stack of well logs.

LogCalc includes:

	 1 - Water Saturation - Archie Method
	 2 - Water Saturation - Ratio Method
	 3 - Tixier Rocky Mountain Method for Sw
	 4 - Old Electric Log Technique
	 5 - Rw from SP curve
	 6 - Microlog porosity
	 7 - Microlaterolog water saturation and porosity
	 8 - Dual Induction Log correction
	 9 - Dual Laterolog correction
	10 - Sonic log porosity
	11 - Density log porosity
	12 - Neutron log porosity
	13 - Neutron+Density Crossplot (2-mineral)
	14 - Pe+Density Crossplot (2-mineral)
	15 - Sonic+Density Crossplot (2-mineral) 
	16 - Sonic+Neutron Crossplot (2-mineral)
	17 - Neutron+Density+Sonic Crossplot (3-mineral)
	18 - Pe+Neutron+Density Crossplot (3-mineral)
	19 - Pe+Neutron+Density+Sonic Crossplot (4-mineral)
	20 - Volumetric Oil Reserves
	21 - Volumetric Gas Reserves
	22 - Rate-Based Reserves
	23 - Shale Gas Estimate
	24 - True Zone Thickness
	25 - Estimate Mud Weight
You get ample resistivity-based routines to interpret old well logs, but LogCalc can do much more. Try this: take data from a Pe curve, a Density log, a Sonic log, and a Neutron log, and then compute rock composition and porosity from a subset of 14 possible minerals! LogCalc gives you the option to correct for shale, and even offers quick routines for reserves, shale gas, true zone thickness, and mud weight.


Each LogCalc program uses input fields, drop-down lists and checkboxes on a vertically scrolling input form. All programs open with example data in the fields, so that you can immediately press the [Calculate] button to see how the program works. (Only subscribers will see the answers). If you make an error, press the "Reset" button to see initial values again. To return to the main menu, press the [Back] button. Each program has a [HELP] button for more information.

If you click or tap on a program name it will run in the same browser window. But you can also have multiple LogCalc routines running at the same time. On a computer, right-click on a program name to pop up a context menu which will let you open the program in another browser tab or in another window. On phones and tablets, press and hold your finger on a program name to bring up the option to open it in a new browser tab (depending upon your web browser).

Why do I like porosity crossplot programs?

Because I hate to waste data!

How do most geologists make log calculations through a thick carbonate? They average the neutron and density porosities, glance at the Pe curve, and say that the rock is a limestone because the Pe is around 5, or a dolomite because the Pe is closer to 3. If there is crossover they call it gas effect. We can do better.

Look at the information we are discarding: a garden-variety neutron and lithodensity log provides enough information to solve for the percentages of THREE different mineral end members, plus porosity, at every depth level! Toss in a sonic log and you can solve for FOUR end members plus porosity. In an organic shale, you could solve for the percentages of quartz, illite, pyrite, and pyrobitumen. LogCalc makes it easy to play with compositions and gain real insight.

Shale correction:

LogCalc's shale-correction uses the gamma-ray curve, since that curve responds to high cation-exchange-capacity shales (which are the ones that affect resistivity). To use the gamma-ray curve for shale correction, remember this strategy:

	Gamma-ray, clean: enter the lowest API value recorded
	on the entire well log, across from the cleanest zone

	Gamma-ray, shale: enter the API value for a shale
	adjacent to your zone of interest
	Shale resistivity: enter the resistivity for the same
	shale, adjacent to your zone
	Gamma-ray of zone: enter the API value for your zone at
	the depth of calculation


Send questions and suggestions to: Scott Schad

Disclaimer: Well logs are only data. You provide the answers. Whether or not you calculate a zone productive, it still has to make geologic sense, and engineering sense, and economic sense, to risk money completing it. Use these programs at your own risk. Good luck to you!

All contents Copyright © 2013-2021 by Scott Schad