Бурение грунтовых зондов, установка энергетических колодцев

1.4.1 Size of Influx:

As stated earlier, the time taken to close in the well should be no more than 2 minutes. If the kick is not recognised quickly enough, or there is some delay in closing in the well, the influx continues to flow into the annulus. The effect of this is shown in Figure 12. As the volume of the influx allowed into the annulus increases the height of the influx increases and the higher the pressure on the annulus, Pann when the well is eventually shut-in.

Not only will the eventual pressure at surface increase but as can be seen from Figure 13, the pressure along the entire wellbore increases. There are two dangers here:

(i) At some point the fracture pressure of one of the formations in the openhole section may be exceeded. This may lead to an underground blow-out — formation fluid entering the wellbore and then leaving the wellbore at some shallower depth (Figure 13).

once a formation has been fractured it may be impossible to weight the mud up to control the flowing formation and there will be continuous crossflow between the zones. If an underground blow-out occurs at a shallow depth it may cause cratering (breakdown of surface sediment, forming a large hole into which the rig may collapse).

(ii) there is the possibility that Pann will exceed the burst capacity of the casing

at surface.

0

	4 >
		4 4
	ANNULUS Gradient of original mud 22 Pressures after closing in. Small influx into the annulus. Pressures after closing in. Large influx into the anulus. Note: Pressures higher at all depths higher due to larger influx
	®	©	v©
			N
				4
					^
					>				>	arge Influx
	— Origin	al Mud d fluid					Sm 1	all Influx J

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Pressure in 1000 PSI

Figure 12 Effect of increasing influx before the well is shut in

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789 Pressure in 1000 PSI

4				1 Original Mud Pressure 2 Closed in Pressure
					(3)	Pressure increase due to gas migration Pressures after formation breakdown — Internal blow-out
		4	>
	>	4
		Ф (	D\	(2 (
			4	N
				>
				N	4	…… 1
							4 ^
	riginal mud vaded gas	V	4
————— I		i	‘l	4 [

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0 1 2 3 4 5 Formation strength after breakdown

-Initial formation strength-

Figure 13 Underground blow-out conditions

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