Page 8 - Well Control for Completions and Interventions

Introduction and Well Control Fundamentals 3

“intervention” and “workover” are used differently by operating compa-
nies and regulatory bodies.
Workover is, for some operating companies and jurisdictions, an opera-
tion that materially alters the structure of the well. Adding perforations,
setting bridge plugs in a liner to isolate unwanted water, or any of a range
of stimulation treatments are all classified as workover operations. For
others, workover means a recompletion, the removal and replacement of
all the major completion components including the production tubing.
This generally means killing the well and using a drilling derrick or
hydraulic workover unit to pull and rerun the tubing. For the purposes of
clarity, where the term “workover” is used in this book, it will mean
recompletion of the well.
Well intervention will mean “through tree” intervention on live wells
using wireline, coil tubing, or a workstring run against pressure using a
hydraulic workover unit. Well interventions also include pumped treat-
ments, stimulation, and well testing operations.
For nearly all of these interventions, well control is provided by pressure
control equipment, for example wireline lubricator and stuffing box, coil
tubing stripper, and when using a hydraulic workover unit, stripper rams or
annular preventer. Operations using live well pressure control equipment are
significantly different from those carried out on a dead well where a fluid
barrier is used, consequently, management of well control and well integrity
must be viewed differently.

1.1.1.1 Pressure control and well control
The terms well control and pressure control are used extensively through-
out this book. For the purposes of clarity, the term “pressure control” is
used to describe live well interventions, where pressure retaining equip-
ment is being used to prevent the escape of pressurized fluids at the sur-
face. It is mainly applicable to wireline, coiled tubing, and hydraulic
workover operations on live wells. “Well control” is generally used in the
context of maintaining a hydrostatic overbalance during operations on a
dead well.

1.1.2 Why interventions and workovers are performed
Workovers and Interventions are performed for two reasons:
1. To repair or replace failed equipment.
2. To increase production, either through improving existing production
or slowing the rate of decline.