Page 298 - Well Control for Completions and Interventions

Well Kill, Kick Detection, and Well Shut-In 291

• Indicated by a uniform increase in SICP and SITP.
• If uncontrolled, pressures will increase everywhere in the wellbore.
• Increased pressure can cause formation damage, loss of whole fluid
into the formation, or damage to surface equipment.
• Occurs rapidly in clear, low viscosity, workover fluids.
Surface pressure is relieved by using either the “constant tubing pres-
sure method” or the “volumetric method.” Both methods are used when
it is not possible to circulate out a kick, where circulation cannot be
started immediately, or where bullheading is not possible or is inadvisable.
It should be noted that increasing pressure, caused by gas migration, is
normally less of a concern during workover or intervention operation
than during a drilling operation. With mud in the hole, increasing pres-
sure acts against the filter cake. Since most filter cakes have extremely
good fluid loss prevention properties, pressure can build to formation
fracture pressure, resulting in fluid loss and formation damage. This is less
likely to happen if clear (solids free) fluid is controlling the well.
Increasing well pressure caused by gas migration normally results in
increasing rates of fluid loss as pore pressure is exceeded. Formation frac-
ture is unusual and only occurs when extremely robust LCM is used, per-
meability is exceptionally low, or the window between pore pressure and
fracture pressure is unusually narrow. In some cases, gas expansion will
self-regulate, increasing wellbore pressure being offset by an increase in
leak-off to the formation.

7.6.1 Constant tubing pressure
This method, as the name implies, removes the gas whilst maintaining a
constant tubing pressure. Although easier to implement than the volumet-
ric method, it can only be used if these conditions are met:
• There is a communication path between the tubing and the annulus
choke.
• Tubing pressure is able to be read.

7.6.1.1 Procedure for constant tubing pressure bleed method
1. Allow SITP to increase by a safety margin of about 50 100 psi
(350 700 kPa). The safety margin prevents any additional influx
caused by bleeding off too much pressure at the choke. This is the
lower limit.
2. Allow SITP to increase by an additional margin, normally about
50 100 psi (350 700 kPa). This is the upper limit.