RE: They are coming soon6 Jun 2023 11:41
Ocelot,
There are two main types of mud system - Oil based mud and water based mud. But below that are dozens of different types of mud systems and hundreds of different chemicals that we can use in them.
In basic terms, hole problems boil down to either mechanical or chemical causes (and solutions).
Mechanical means that the hole is unstable because too little or too much (or both!) mud weight is being used for the conditions.
Chemical means that the formation is reacting with the mud system in some way.
For example, you can drill from one shale that was laid down in a fresh water environment into another that was laid down in a salt water environment.
So if the mud is a freshwater mud, when you drill into the shale that was laid in a saltwater environment, osmosis means that the shale will absorb water from the mud and swell up.
Conversely, if you drill using a salt water system, when going through the freshwater shale the mud will absorb water from the formation and dehydrate it - essentially causing it to dry out and fall into the well bore.
Both these effects can be time dependent, some shales are quite benign and take several days to react. Others react much more quickly.
In my early days drilling in the Southern North Sea, we had two different types of shale in the same hole section. One of them reacted very quickly and we knew we had 36 hrs to drill through it and get the casing in before the hole fell apart.
Each area is different - even the same Shale formation can react differently in different areas and have different problems.
So in that respect what worked in one area won't necessarily work in the other area.
I don't know what the basic problem was in SFB, but considering it was a development Well I was surprised they had so many issues - possibly it was the first time they'd drilled deviated Well in that particular direction, which can have a big effect on hole stability due to local Geomechanics.
Apologies for being a long, boring post, but Drilling Fluid is a complex subject with many manuals being written on it over the years.
If you have nothing better to do, there are some decent introduction to drilling fluids videos on YouTube.