Here's a question we get all the time:
(hands thrown in the air)
We drilled all of our wells in the same direction and did everything the same, so why did some have problems and others didn't?!
And here's an example map of "all of our wells in the same direction:" (Note, these wells were picked randomly; we have no idea whether any of these wells actually had problems.)
There are two main things to consider:
1: Problems are very often in the build sections.
2: The build section orientations are all over the place.
So here's the plot promised in the title:
What is it? It's a lower hemisphere stereonet that shows the mud weight needed for all possible hole orientations at a given depth to prevent serious stability problems. There aren't numbers on it, because the numbers are very specific to an actual place and rock, but for some perspective the range in this example is about 300 kg/m3 (2.5 ppg). A well deviated 60 deg to the northwest (yellow) requires about 150 kg/m3 higher mud weight than a well deviated 60 degrees to the southwest (blue). This might not seem like much, but if you err on the low side, the costs can be tremendous (can you say sidetrack?).
In a detailed study of more than 100 Duvernay wells*, it was found that $17.1 million CAD was spent on "mechanical" non-productive time (NPT) like rig downtime and such. Ouch, but probably in large part unavoidable. In the same wells, however, $18.5 million was spent on those same wells on NPT due to "formation" related problems - in other words, primarily geomechanical problems. What if most of it was avoidable?
*If you want to know what study, contact Amy and she can put you in touch with the author.