Page 220 - Well Control for Completions and Interventions

Completion, Workover, and Intervention Fluids 213

formula described in Chapter 1, Introduction and Well Control
Fundamentals, can be used to calculate tubing and casing capacity.
During a completion or workover, there will be occasions when no
tubing or drill-pipe is in the well. If losses were to occur at that point,
the potential exits for the entire volume of the casing (and liner if run)
from surface to the formation to be lost. Therefore, when calculating the
wellbore circulating volume, the worst case assumption is based on casing
capacity, that is, no allowance is made for drill-pipe or tubing displace-
ment volume.

5.10.2 Surface piping
The volume required to fill the surface lines is normally small, unless the
equipment needs to be positioned a distance from the well. In any case,
the surface line volume should be included in the total circuiting volume.

5.10.3 Holding tanks
Where a brine is filtered, additional pits are used to store the brine. One
tank is needed to store dirty brine coming back from the well, and a sec-
ond tank for filtered brine ready for pumping into the well. This pit vol-
ume needs to be included in the total brine circulating volume. The
volume should include any dead space in the tanks.

5.10.4 Filtration capacity
If brine is being filtered during circulation, then the capacity of the filtra-
tion system needs to be included in the total brine circulating volume.
2
Large capacity (1500 ft ) press filters hold approximately 34 bbls of fluid.
Precoat and body feed tanks require an additional 20 bbls. Cartridge filter
units hold about 4 bbls. A two-stage filtration system (press and cartridge)
will therefore use almost 60 bbls of fluid.

5.10.5 Contingency
A volume of brine over and above the circulating volume needs to be
stored at the wellsite, to enable the hydrostatic overbalance to be main-
tained in case of fluid loss to the formation. Keeping the hole full is cru-
cial. If losses do occur, then it may be necessary to place LCM at the
reservoir before they will stop. A worst case assumption is that losses
begin when no drill-pipe or production tubing is in the well; there is no
ability to circulate in a kill pill. In this case it may be necessary to control