Page 196 - Well Control for Completions and Interventions

CHAPTER FIVE

Completion, Workover, and
Intervention Fluids

5.1 INTRODUCTION
Nearly all completions are run with a clear solids free, brine in the
well. During workover operations, brine is used to kill the well and
remains in the wellbore until the new completion has been installed.
Brine is also used as a packer fluid; the fluid left in the annulus at the end
of the completion or workover. Finally, brine is used for perforating,
gravel packing, and fracturing operations.
For many completion and workover operations, a brine column is the
primary well control barrier. Where brine has a well control function, it
must be dense enough to overbalance the formation pressure by a margin
sufficient to prevent an influx. Since brine is nominally solids free, any
overbalance pressure acting against a permeable formation will result in
fluid loss to the formation. Uncontrolled or unmonitored losses would
mean a loss of hydrostatic overbalance, causing the well to kick. Fluid loss
can also damage the formation, and consequently reduce productivity.

5.2 BRINE SELECTION
Where brine forms the primary well control barrier, the first step
in selecting a brine is to calculate the density needed to overbalance for-
mation pressure. Brine density is calculated with respect to well depth
(true vertical depth, TVD) and reservoir pressure (bottom hole pressure,
BHP). Once brine density has been calculated, it must be adjusted to cor-
rect for wellbore average temperature and pressure. With this done, a
suitable brine can be selected.
A wide range of brine densities can be achieved by dissolving different
salts in freshwater (Table 5.1).

Well Control for Completions and Interventions. © 2018 Elsevier Ltd.
DOI: https://doi.org/10.1016/B978-0-08-100196-7.00005-1 All rights reserved. 189