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Well Interpretation – Structural and Stratigraphic Mapping


There comes a time in every geologist’s life where he is forced to look at a bunch of well logs and make some sense of them and the surrounding geology. (OK, that time usually comes fairly early in their career – maybe the first day). No matter if you are looking for structural traps, stratigraphic traps or looking at one of the unconventional shale plays it all starts out looking at a well log.

The Black and White Past

well logging

Interpreting information from wells logs has gotten both easier and harder at the same time. I remember those days when you use to take a bunch of paper logs, hang them on the wall and tried to correlate the various formations. The hardest thing was to get all the logs copied at the same scale (2 inch for regional work, 5 inch for field or development work). Then there was normalizing the logs to account for different tools and different contractors. My favorite (actually least favorite) was the SP shift that always seemed to happen right in the middle of the zone I was interested in.

well interpretation

Then there were the tools of the trade, to mark your formations. I recall someone expensing colored elastic string and having accounting deny the expense as something that was not an approved office expense. He turned around and resubmitted it as “elasticized stratigraphic correlation markers” and it was approved immediately – apparently accounting knew what that was. Paper logs had lots of holes at the top from the countless times it had been pinned to the wall (when you traded logs with someone and the logs you got didn’t have pin holes in them, you knew you were getting great stuff).

There were some good things also – there was only a handful of different types of logs, there weren’t that many wells and splicing multiple runs together involved a fold and scotch tape. Ah, the good old days.

It’s 2014 – Things Sure Have Changed(?)

Today I have three 29 inch LED monitors that stretch across my desk and show more wells than I can even imagine (OK, I just lied about the 3 monitors. However, I did have it on my Christmas wish list this year. Apparently in the naughty/nice decision, things went badly for me and I continue to use my two 19 inch monitors but I harbor no ill will SANTA!).

The reality today, the more screen real estate you have the better off you are going to be (just like wall space in the old days). Monitors are better, bigger and cheaper. I have seen some office configurations that are amazing and allow construction of sections that we could only put up in a conference room if we were forced to go back and use paper.

gas well interpretation

Logs today are actually a lot more complex for the average interpreter. Who invented all these logs? Petrophysicists are giving the geophysicists a run for their money on who can consume the most disk space. Logs that view 360 degrees of the borehole for each depth sample taken give an amazing view of the rocks that the interpreter has never had before. There are also more log types. Thankfully packages like Transform Essential have simple ways to alias various types of curves so that all the Gamma Ray curves, for example, all end up together so different names with the same log type isn’t such a big deal. Transform is even going to do your log normalization for you – look for it in a release coming soon.

Splicing multiple runs back together might be something you never need to worry about. LAS logs that Drillinginfo has processed in the past 4 years are all spliced together for you already. So you might not actually have this problem.

Remember “elasticized correlation marker”, well those days are gone. Geophysicists have an auto-picker for seismic, so now the geologist has an auto-picker for well logs. The formation top picker allows the geologist to make a single pick and the system will make the equivalent pick in the surrounding well logs. You can even bracket picks. Surfaces that are harder to pick can be focused above, below or between 2 formations that have already been picked.

cross plot oil well log

The trick to using a system like this is to have the system identify the top of easily identified regional markers then go back and have the system pick more subtle markers between the regional picks. What took days/weeks now takes minutes. Maps can then be easily created allowing the geologist to quickly find any problems that might have occurred. This allows the geologist to be more of an editor instead of being the person that does the picking.

I confess, I hated picking tops. The first few days were fun, the second week was ok but week 15 made me wish for the days when some machine would do this for me. The fun part for me was looking at the logs and figuring out the EOD (environment of deposition), how the rocks were deposited and then what happened to them – was porosity preserved or was the porosity secondary? Were the rocks tilted? Where did the hydrocarbons come from and how were they trapped? That is the fun part and that is the part that still requires a geologist to piece together the geological puzzle from the logs, cuttings, cores or any other piece of data that we can get from the wells and seismic.

No more spending mindless days/weeks picking tops, welcome to the good old days.

Bonus Secret

Every once in a while I like to pass along a secret on how to get some added feature that you might not know about. This one has to do with free log data. For those of you that are Pro customers, you have it made. You can look at any well / LAS data in Drillinginfo’s huge library. However, for those that are not Pro customers, there is a way to view a lot of the LAS Gamma Ray curves in our library. Click on the 2.0 button and view all the wells. You can then window the map as you would in any web map. When you click on the + just to the left of the layers menu, some of the wells will go away leaving only the wells that have LAS curves. Click on any well and a tiny cross section will appear showing the Gamma Ray log for that well just below the map window. You can’t export it but you can take a look at it.

Your Turn

What do you think? Leave a comment below.

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John Fierstien

is the Director of Data Inventory. He has worked as a geologist for several E&P companies and as someone who has been helping to create some of the best tools for geologists and geophysicists to help them find oil and gas. He received his Bachelor of Science in Biology and Geology from Central Michigan University and his Master of Science in Geology from the University of Pittsburgh.