Page 299 - Well Control for Completions and Interventions

292 Well Control for Completions and Interventions

3. Using the choke, bleed the annulus until the tubing pressure drops to
the lower limit. There will be a time lag between bleeding off pressure
at the choke and seeing a response on the tubing pressure gauge. The
time taken for the pressure signal to reach the tubing head is depen-
dent on the depth of the tubing (or the circulation port) and the char-
acteristics of the fluid in the well. To avoid bleeding off too much
pressure on the annulus side, close the choke when the annulus pres-
sure reads the lower limit and wait until the tubing pressure stabilizes.
4. Keep repeating steps 2 and 3—keeping the tubing pressure between
the lower and upper limits for as long as is necessary or until gas
reaches surface.
As the operation progresses, the casing gauge will show an increase
even though the tubing pressure remains within the upper and lower
limit. Do not try to keep the pressure on both sides the same by opening
the choke. With successive bleed cycles, the gas expands as it rises
in the annulus, creating an imbalance in HP between the annulus and
the tubing.

7.6.2 Volumetric method
If there is no communication between the tubing and annulus, the volu-
metric method must be used. Control is managed by accurately recording
the volume removed with each bleed cycle. A calibrated tank placed
downstream of the choke is needed, and it should be capable of recording
1
fluid volume in relatively small increments, from as little as /2 bbls or
3
0.8 m .
Outline procedure:
1. Select a safety margin. Normally 100 psi (700 kPa).
2. Select a range, also normally about 100 psi (700 kPa).
3
3. Calculate HP (P h ) per bbl or (m ) fluid in the upper part of the
annulus:
P h per bbl (psi/bbl) 5 fluid gradient (psi/ft.) 4 annular capacity fac-
tor (bbl/ft.).
3
3
P h per m (kPa/m ) 5 fluid gradient (kPa/m) 4 annular capacity
3
factor (m /m).
4. Calculate volume to bleed to reduce pressure by the range:
Volume to bleed (bbl/cycle) 5 range (psi) 4 P h per bbl.
3 3
Volume to bleed (m /cycle) 5 range (kPa) 4 P h per m .
5. Construct casing pressure versus volume to bleed schedule.