Monday 12 November 2012

Isopach maps vs isochore maps

Thickness maps are a fundamental tool in structural geology. They represent thickness variations and thickness trends of a given unit. Isochore and isopach maps are two different types of thickness map. To make it clear from the beginning:


  • An isopach is a line that connects points of equal true thickness (i.e. measured perpendicular to bedding), whereas...
  • an isochore is a line that connects points of equal vertical thickness

Fig. 1.- A constant thickness layer is drilled at different angles by three wells
Figure 1 depicts a perfect cilindrical fold, where the western flank dips more than the eastern flank. Well 1 cuts the yellow bed at a higher angle than well 3, and therefore, the vertical thickness found in well 1 is larger than in well 3. Well 2 cuts the bed where is horizontal, and therefore the vertical thickness equals the real thickness. The real thickness of the yellow bed is constant: 500 m.

If we would do an isopach map of the yellow unit, it would show a constant value of 500 m, because this unit doesn't show any thickness (true) variation... It would be a pretty boring map :-). But it would be telling us quite a lot already; for starting, we could think we are dealing with a parallel fold formed by flexural flow (for example).


Fig. 2-. Isochore map for the yellow unit in figure 1.
Figure 2 shows the isochore map -contours for equal vertical thickness- for the yellow bed depicted in figure 1. Red colour indicates minimum vertical thickness, whilst purple shows maximum value. You can see that it shows what you can see in the cross section: we would measure increasing vertical thickness as we move away from the hinge of the fold, as the dip of the bed increases and therefore we would cut the yellow bed at a higher angles.

We can see that the difference between an isopach map and an isochore map is quite obvious and simple to understand. Unfortunately, some people interchange both terms, and too many times we can see isochore maps refered to as "isopach maps"

If we would get the map from figure 2, and somebody would tell us that this is a isopach map over and anticline, we could wrongly conclude that the real thickness around the hinge line of the fold is smaller than in the flanks, and we would probably think that we have in front of us as growth anticline, for example. 

Another error may come from working with seismic surveys and not realising that if you take a surface representing a top unit, and you substract another surface representing a bottom unit, the result is a isochore map, not a isopach map.

Hence... how many structures have been wrongly studied, how many wells haven't reached a target because somebody used wrong a simple word? Better not even to know it! And this is considering that everytime we read a vertical thickness in a well log the well was actually vertical and not deviated at all. If you take a surface representing a top unit, and you substract another surface representing a bottom unit, the result is a isochore map, not a isopach map.

If you have any question, just ask in the comments. If you have any suggestion for a new article, just let me know. You are also welcomed to write some contribution!







26 comments:

Matt Hall said...

Nice post — I think 'isopach' is one of the most often misused words in exploration geoscience. And that wouldn't necessarily be a huge problem, if I didn't suspect that it reveals a basic misunderstanding of what has been mapped. So, thanks for the nice tutorial.

I've tried in the past to correct an isochore map to an isopach map by multiplying by the cosine of the dip. This sounds easy enough, but it doesn't make for a perfect correction, because it's not always obvious how to compute the dip (upper surface? Lower? Average?), and it's messy around faults. Best to correct at the wells, then interpolate.

Matt

Jorge said...

You mention a very good issue... If we consider vertical thickness in an isochore map, we can only project a given value to a single point in the surface.
But, as you say, the problem comes with real thickness. Where do we project that value? Vertically from the top? from the bottom? Middle way?
Thanks for the comments, is very welcome!
Jorge

Scott said...

Excellent description of a basic and critical facet of geology as it relates to mapping analysis.

Unknown said...

Thanks a lot for a clear explanation. My problem is I am not able to visualize the isopach map. The way its drawn is fine with me but how to see the contours whether projected on surface or direct subsurface projection. Please help me understand.

Unknown said...

Isochore Map is the term adapted in my reports since 2006. This after I read a similar article differentiating Isochore vs Isopach.
I have a question though, if the upper and lower bounds are non-parallel, is it safe to say that one cannot create an isopach map of the structure, because we would either be measuring a point perpendicular to the upper or lower bound, but not to both.

Unknown said...

Super Bowl 51



Patriots vs Falcons



Super Bowl 2017



Falcons vs Patriots



Watch Super Bowl 2017



Super Bowl 2017 halftime show



Super Bowl 2017 Live

Live Streaming HD said...

super bowl 2017



super bowl 2017 live



super bowl 2017 time



2017 super bowl



watch super bowl 2017

Live Streaming HD said...

Grammy 2017 will be at 5:00 PM - 8:30 PM on Sunday, February 12, 2017 in Los Angeles at the Staples Center. Read more:



Grammys

Grammy 2017

Grammys 2017

2017 Grammys

Watch Grammy 2017

Grammy Awards

Grammy Awards 2017

Anonymous said...

Now why we call ourself as the hub of call girls in Gurugram because we dote our job to provide best to our clients and for this we maintain a list of the best and affordable call girls in gurgaon city.
Gurgaon Escorts
Aerocity Escorts
Mahipalpur Escorts
Connaught Place Escorts
Paharganj Escorts
Russian Escorts in Gurgaon

Anonymous said...
This comment has been removed by the author.
Unknown said...

Bhopal escorts
Bhopal escorts Service
Bhopal escorts Agency
Bhopal Call Girls
Independent Bhopal Escorts
Rishikesh escorts
Rishikesh escorts Service
Rishikesh escorts Agency
Rishikesh Call Girls
Independent Rishikesh escorts
Nainital escorts
Nainital escorts Service
Nainital escorts Agency
Nainital Call Girls
Independent Nainital escorts
Nasik Escorts
Nasik Escorts Service
Nasik Escorts Agency
Nasik Call Girls
Independent Nasik Escorts
Dehradun escorts
Dehradun escorts Service
Dehradun escorts Agency
Dehradun Call Girls
Independent Dehradun escorts

Anonymous said...

Gurgaon Escorts
Gurgaon escort service
escorts in Gurgaon
Gurgaon call girls
Call girls in Gurgaon
Aerocity Escorts
Aerocity escort service
escorts in Aerocity
Aerocity call girls
call girls in Aerocity
Russian Gurgaon Escorts
Russian Gurgaon escort service
Russian escorts in Gurgaon
Russian Gurgaon call girls
Russian call girls in Gurgaon
Paharganj Escorts
Paharganj escort service
escorts in Paharganj
Paharganj call girls
Call girls in Paharganj
Mahipalpur Escorts
Mahipalpur Escort service
Mahipalpur Call Girls

Unknown said...

Gurgaon Escorts
Gurgaon Escorts Service
Gurgaon Escorts Agency
Independent Gurgaon Escorts
Gurgaon Escort
Gurgaon Call Girls
Female Escorts in Gurgaon
Independent Escorts in Gurgaon
Call Girls in Gurgaon
Escorts in Gurgaon
Call Girl Services in Gurgaon
Gurgaon Escorts Services
Electronic City Escorts
Escorts in Electronic City
Electronic City call girls
Manesar call girls
Manesar escorts
escorts in Manesar
DLF city escorts
escorts in DLF city
DLF city Call Girls
Palam vihar Call Girls
Palam vihar escorts
escorts in Palam vihar
escorts in sohna road
sohna road escorts
Sushant Lok Escorts
Sushant Lok call girls
udyog vihar call girls
udyog vihar escorts
escorts in udyog vihar

Anonymous said...

Gurgaon Escorts
Gurgaon Escorts
Gurgaon Escorts
Independent Aerocity Escorts
Aerocity Escorts Service
Aerocity Call Girls
Russian Gurgaon Escorts
Russian Gurgaon escort service
Russian Gurgaon call girls
Paharganj Escorts
Paharganj escort service
Paharganj call girls
Mahipalpur Escorts
Mahipalpur Escort service
Mahipalpur Call Girls

Muhammad Zakariyya said...

How can I generate isopach maps manually if am given data to do so

Rustandi Ramadhan said...

Hi jorge,
have you any refference to know more about isopach like its advantages, its resources, and many more?

Hotelescortservices.com said...

Guwahati escorts
Guwahati escort
Guwahati escort services
Guwahati call girls
Guwahati call girl
Call girls in Guwahati
Call girl in Guwahati
Call girl services in Guwahati
Escort services in Guwahati
Escort service in Guwahati

================
Guwahati escorts
Guwahati escort
Guwahati escort services
Guwahati call girls
Guwahati call girl
Call girls in Guwahati
Call girl in Guwahati
Call girl services in Guwahati
Escort services in Guwahati
Escort service in Guwahati

==================
Guwahati escorts
Guwahati escort
Guwahati escort services
Guwahati call girls
Guwahati call girl
Call girls in Guwahati
Call girl in Guwahati
Call girl services in Guwahati
Escort services in Guwahati
Escort service in Guwahati

koyal rani said...

Movies Buddy is one of the best platform for downloading latest bollywood movies, Hollywood and Tollywood HD movies. We are very happy to provide you latest movies, latest tv shows, latest web series. Please Join on Movies Buddy Telegram group. Jharsewa || Back Figure || Mithilesh Singh || LPG Vitarak Chayan || Sex Videos

holdpuris said...

This will be useful for all We are an individual stockbroker who is providing trading-related services in the Indian stock market where you can come directly to us for solutions to trading-related problems and Demat account. We deal with stocks and Initial Public Offerings other financial markets
Thank you for this article. Stock Market

Meet Me World Business said...

Mithilesh singh

hillgibson said...

Online learning is a completely different game. Finding efficient study methods when learning remotely is one thing, but studying for quizzes in the current remote learning environment that may be proctored or un-proctored and very different from any others you have taken is quite another. This is why you may ask someone to do my online quiz for me so that you can score well in the course.

russian escort service said...

ffjhghg

cad software for mechanical engineers said...

Structural Geology is a captivating field that unveils the secrets of Earth's geological history and processes. It focuses on the study of rock deformation, tectonic forces, and the arrangement of geological structures. From fault lines to folds and fractures, Structural Geology allows us to understand the forces that shape our planet's crust.

kevin smith said...

Best Platform For your Grow
Ndax login
Ndax login
Bybit login
Luno login

kevin smith said...

Bitbuy is a special app for your phone that helps you buy and use a type of digital money called cryptocurrency. Imagine it as a digital piggy bank, but it’s not for regular coins or bills you can touch.

Kala Kutir said...

Thank you so much for sharing such an nice information. Visit Kalakutir for Industrial Floor Marking, Industrial Painting, and Bus Branding and more services information in detail.
Bus Branding