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Underground Blowout
22 January 2017
Good morning. I have 2 questions which are referring to underground blow out. First, to have an underground blow out, is If you haven't calculated correct the kick tolerance. For example your well can withstand 40 bbl and you got 50 bbl. My question is, after you have shut in the well, you can have an directly fracture of the formation under the shoe, or during the circulation of the kick out to the surface, when the kick is in the casing shoe, then you fracture the formation (because the kick has the same pressure).
My second question is when you have a pressure of formation a little bit higher than expected, but still you dont have any problems because your mud pressure is still higher, when its time for shift handover are they gonna recalculate the kick tolerance? 
Thank you for your time

3 answer(s)
company man
National Iranian Oil Company
Total Posts: 2
Join Date: 23/01/16
In fact, underground blowout &broching may happen in shallow wells that have the gas pocket.
These gas pockets usually have a high pressure and low volume.
After closing well due to breakage of layers, gas or oil reaches the surface and in the most optimistic way, it causes environmental pollution.
An underground blowout occurred at this stage.
Perhaps it would be better to burn oil or gas that is spreading from the gaps in the location, this contributes to lower environmental pollution.
Of course, this depends on where and from what location the gas or oil have reached the surface of the well.
It can explode quickly when the gas reaches the surface, perhaps one of the ways to secure a well instead of closing it is to use a diverter.
Poor boy degasser can be used to separate fluid from gas and oil in return.
If someone has an experience close to this, I would like to express my thanks.
What is the best way to secure wells?

company man
National Iranian Oil Company
Total Posts: 2
Join Date: 23/01/16
Japp, suppose we are drilling in the top hole and the well erupts, We know that the driller should not close the bop stack because it causes an underground blowout.
The closing of the bop stack will break the weaker formations and trapped gas reach surface.
It causes the rig to burn.
What is the best way to secure wells?
The real case of this problem occurred in 1975 in the Aghajari Field in Iran, Due to the closing of the bop stack, gas reached the surface and the oil rig burned.
As you know, increasing the weight of the mud increase loss and as a result, the blowout increases.
It should be considered that the process of making mud needs time.

Head of Well Engineering
State Supervision of Mines
Total Posts: 13
Join Date: 09/11/15
Alexis, your questions are not totally clear, but I'll do my best:
Underground blow-out: This is the name for the event where you have through your well created a situation where there is an uncontrolled flow from one layer (say gas from a gas reservoir) into another layer (say a permeable sandstone layer higher up in the well). This can happen for instance when you increase the mudweight to control the gas pressure in the gas reservoir. The permeable layer higher up breaks under this higher mudweight. this causes losses, lowering the pressure in the well. Now the gas can enter the well and starts travelling up. The driller closes in the well, but the mud and the gas keep flowing into the weaker formation.
Another scenario could be what you sketch, that you have a kick in the well, and that you break down the formation higher up while circulating out the kick. 
In real life, the potential for an underground blowout is far higher in the first example: Formation breakdown and losses due to too high a mud weight occurs far too often. Luckily there isn't always a oil or gas reservoir open to start flowing...
As to your second question: On shift handover the crew should perform a slow-circulation rate test. The kick tolerance recalculation should happen any time the mud weight is changed.
Posted by

Alexis Koulidis



Total Posts: 11
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