Page 221 - Well Control for Completions and Interventions

214 Well Control for Completions and Interventions

losses by pumping a kill pill into the casing at surface and waiting for it to
reach the formation. The entire wellbore volume must be lost to the for-
mation before the kill pill can work. For this reason, at least twice the cir-
culating volume should be considered as a minimum requirement for
brine quantity. In many instances, where losses are continual or difficult
to control, considerably more fluid will be required.

5.10.6 Brine volume summary
Consider preparing a simple spreadsheet itemizing and quantifying brine
volume requirement. The spreadsheet can incorporate simple tubing and
casing capacity calculations. The total volume would include:
1. Wellbore capacity
2. Surface lines
3. Holding tanks
4. Filtration unit capacity
5. Contingency.

5.11 ALTERNATIVES TO BRINE

For fluid to be classified as a well control barrier, it must be moni-
tored. In practical terms this means the fluid level must reach the surface,
where it can be observed. If the reservoir pressure is too low to support
the hydrostatic pressure that results from a full column of water based
fluid, then a lower density alternative must be used if a fluid barrier is
used. Nonwater based alternatives can be used across a range of lighter
than water densities (Table 5.8).
Under exceptional circumstances, mud is used as a completion and
workover fluid, normally where there are major safety concerns associated
with well control. For example, in the Chevron operated Tengiz field

Table 5.8 Alternatives to brine (lighter than water)
Material Density range (ppg)

Nitrogen gas 0.1 2.6
Foam 3.5 8.3
Kerosene, diesel, or base oil 6.7 7.1
20 API stock tank crude 7.8
30 API stock tank crude 7.3