Does anyone on here work on the drill floor of a rig or have any experience of oil wells? Just curious as to whether you are able to tell when you’re going through an oil reservoir through mud returns/pressure change etc or whether its a case of waiting until you test. I’ve got a vague understanding of the principles behind the process but it’s the finer detail i’m curious on.

i expect a few on here know more about it than I do but seeing as no one else has replied yet:

Yes you will be able to see that you are in the reservoir by drill cuttings returned in the mud a surface, it will have a bit of a delay as the cuttings have to make it all the way up the hole to surface.

Seismic and any nearby wells mean they have a fair idea where the reservoir(s) are going to be before they drill generally.

Not so much for cheap onshore wells but for the high end deepwater stuff logging While Drilling (LWD) is so advanced these days that they can get real time measurements of pretty much everything, porosity, permeability, resistivity, saturation etc.

Having said all that I have been offshore on rigs when all the indications were a good well but when the well went on test nothing happened, so I guess its not foolproof. And just because there is some hydrocarbon there, doesn’t mean it will flow to surface, and definitely doesn’t mean it will be economic to produce.

What with accuracy of seismic surveys, directional drilling,geology, MWD, LWD, as mentioned above they pretty much know exactly when they are about to hit the formation, they will even drill around a certain formation to get to what they want, it’s all very scientific these days, well North Sea drilling anyway, it’s still very much ” we gota gusher” with the land based stuff in the states.