Page 268 - Well Control for Completions and Interventions

262 Well Control for Completions and Interventions

Although the point at which annulus HP peaks and begins to drop
can be calculated, the variables involved mean that the calculations are
complex and unlikely to be carried out at the well site. However, in this
example, a casing pressure should be observed before 114.21 bbls have
been pumped. Failure to observe wellhead pressure after pumping this
volume would indicate that the plug was leaking and fluid was being lost
to the formation.

7.3.9.4 Kill fluid at the sliding side door
• When kill fluid fills the annulus, pressure will be as follows:
• Annulus HP: 10,300 ft. 3 0.5546 psi/ft. 5 5712 psi.
• Tubing HP: 10,300 ft. 3 0.67 psi/ft. 5 6901.
• Pump pressure required to circulate fluid: 6901-5712 5 1189 psi.
• Annulus volume is 10,300 ft. 3 0.0414 bbls/ft. 5 426.42 bbls.

7.3.9.5 Displace tubing to kill weight fluid
As the lighter kill weight fluid passes through the SSD and replaces
the heavy packer fluid in the tubing, hydrostatic pressure will drop. Once
the tubing is full of kill weight fluid, the HP at the SSD should be the
required 200 psi overbalance.
• Before kill fluid enters the tubing, HP is 1189 psi higher than
the annulus HP:
• 1189 psi/10,300 ft. 5 0.11 psi/ft. density difference between the
fluid in the tubing (0.67 psi/ft.) and the fluid in the annulus
(0.5564 psi/ft.).
• 1 bbl of fluid pumped will fill 45.05 ft. of tubing reducing the HP
(and therefore casing head pressure) by 45.05 3 0.11 5 5.07 psi.
• Tubing volume is 10,300 ft. 3 0.02125 bbls/ft. 5 218.87 bbls.
• Casing pressure against volume pumped can be plotted. Since the kill
is carried out using overbalance fluids, and as the well is plugged, there
is no tubing head pressure to record (Fig. 7.6).

7.3.10 Example 3 reverse circulation: deviated well with
tapered string
Well kill calculations associated with vertical wells are relatively straight-
forward, since the relationship between pressure and depth remain con-
stant throughout. In deviated wells, pressure change per volume pumped
changes with changing well angle. As the well angle builds (increases)
more kill fluid must be pumped in order to achieve pressure reduction at