Can a Drillstring get stuck in the Borehole? (Differential Sticking)

[Music] welcome to the episode of phone with drilling engineering when drilling all sorts of things can go wrong in the worst case it can happen that the journal string gets stuck in the butthole and no matter how much you try you just cannot freeze again when that happens it's most likely that this stockpipe event was caused by an effect called the french are sticking in this episode we want to briefly explain this the effect of differential sticking is caused by the differential pressure between the drilling mode and the butthole and the formation fluid pressure in the pore of the rock it can be best explained with a suction cup if i take such a suction cup and press it against a smooth wall then the air under the cup is compressed and it probably would escape through the edge of the cup when i let go of the cup the cup will spring back up but due to the tight ceiling between the smooth wall and the cup no air can flow out and this results in a vacuum under the suction cup in other words the air pressure on the outside of the cup is greater than the air pressure on the inside of the cup as a result the suction cup is pressed against the wall it firmly sticks on it and it's not easily removed so now you may wonder what has this got to do with our dress string in the butthole well here we have a sketch of such a deep butthole these buttholes are always with a special field called drilling mode this ruling mode is still not made for the swift application and its density is adjusted such a way that the pressure in the butthole is always slightly greater than the pressure in the formation fluid this is important to prevent any oil and gas from engine to our borehole during during operation this is good but due to the overpressure the boho will now suffer some mud losses into the formation but don't worry the solids in the drilling mode will ensure a tight filter kick quickly beats up which seals the butthole so that the loss of mud in the formation stops now in our butthole we have a drill string as long as it remains in the center everything is okay and nothing will go wrong but as no butthole is truly vertical the drawstring will sooner or later move sideways and lean against the boho wall after some time it's quite possible that the driftstring sinks deeper into the soft filter kick and these can become a problem this is what we see here in this picture on one side is high mud pressure acting on the drill string on the other side smaller formation pressure acts on the drill string and between the two pressure levels is a filter kick which acts as a seal this is just like the suction cup scenario with high pressure on one side and the vacuum on the other side so this situation is similar to suction cup our butthole our d string is pressed against the bottom wall so that it cannot be moved and it is stuck this is a mess so the question is how can we avoid such differential stick in our bow hole we all know that the suction cup only sticks to smooth surfaces when i press the suction cup against the rough outer surface of this bowl like this it will not stick at all this is because there is no effective ceiling and air can flow behind the suction cup there is no stable vacuum under the cup and due to the lack of missing differential pressure the cup will not stay in place it will fall off like this we do the same in our deep butthole either the butthole wall or the drillstring surface needs to be rough we do not have access to the butthole wall therefore we can modify the surface of the drill string in fact typical drill collars are manufactured in such a way that they are spirals on the outer surface as you can see in this picture and these spirals make sure that some of the drilling mode can always flow through the back side of the drawstring even when it's leaning against the butthole wall therefore the fracture pressure cannot beard up and the drawstring cannot easily get stuck similar to the suction cup which will not stick to a rough surface just like that so now let's go back to our first slide from what we have learned today we can easily see that this picture must be a fake first of all i'm not strong enough to pull a drew pipe with my limited muzzle power secondly the fracture sticking would not have happened on this world here as you can see on the right side of the picture we have spiritual colors which were used in the drill string therefore the fragile sticking should not have been an issue all other things being equal this and many other things we'll learn here in our lecture basics of drilling engineering here in freiburg we'll be happy to see you here look off you

Channel: Fun with Drilling Engineering

Views: 2,011

Keywords: drilling, differential sticking, sucktion cup, freiberg, matthias reich, prof. reich, geotechnics, mining, fluid mining, natural oil, gas, borehole, filter cake, drilling rig, drilling mud, drillstring, geo energy system, geothermal, well, bergakademie

Id: J8zuTXVb72k

Length: 5min 0sec (300 seconds)

Published: Mon Feb 07 2022