Page 264 - Well Control for Completions and Interventions

258 Well Control for Completions and Interventions

the annulus will change the pressure profiles observed during the kill and
the differential pressure across the SSD before it is opened.

7.3.9.1 Calculate tubing and casing pressure before and after
opening the sliding side door
• Tubing pressure at the SSD before it is opened is 5500 psi (as per
Example 1).
• Annulus pressure at the SSD:
10; 300 ft: 3 0:67 psi=ft: 5 6901 psi:

• Differential pressure from annulus to tubing is therefore
6901 2 5500 psi 5 1401 psi.
• Since differential pressure across the SSD is high, opening the ports
would risk blowing the wireline toolstring up the hole. To eliminate
this risk, pressure must be applied to the tubing to balance casing and
tubing pressure. Before opening the sleeve, tubing head pressure
(1900 psi) must increase by an amount equivalent to the differential at
the SSD, i.e., 1401 psi. Tubing head pressure is increased to 3301 psi.
• Tubing pressure at the sleeve becomes:
(10,300 ft. 3 0.3395 psi/ft.) 1 3301 psi 5 6901 psi, which is on bal-
ance with the annulus pressure at the sleeve before opening.
Increasing tubing pressure to equalize between tubing and casing will
result in more overbalance than the 200 psi used to keep the well dead, in
this case 1401 psi. The ability to apply tubing pressure is reliant on the
integrity of the mechanical plug. A leak past the plug would result in fluid
losses to the formation with the associated risk of formation damage. It
could be argued that if there is confidence in the integrity of the plug there
is no need to maintain the 200 psi overbalance at the SSD. Wellhead pressure
could be bled-off after opening the SSD. However, should the plug leak, the
resultant hydrocarbon influx would compromise the kill operation.

7.3.9.2 Calculate the fluid level (H) in the annulus if the tubing head
pressure is bled to 0 psi
If, after opening the sleeve, the tubing pressure was bled down, heavy
fluid in the annulus would U tube until hydrostatic pressure is equalised.
The oil water contact depth in the tubing and fluid level in the annulus
can be calculated (Fig. 7.3):
2 2
• Annulus capacity: 8.535 2 5.5 /1029.4 5 0.0414 bbls/ft.
2
• Tubing capacity: 4.678 /1029.4 5 0.02125 bbls/ft.