Page 47 - Well Control for Completions and Interventions

38 Well Control for Completions and Interventions

2
2

CasingID 2 Tubing1OD 2 Tubing2OD 2
AnnularcapacityinL=m5
1273
(1.30)
Example volume calculation
1
How much liquid is needed to fill up 5000 ft of 5 /2v 17 lb/ft tubing, ID
4.892v.
4:892 2
5 0:02324 0:02324 3 5000 5 116:24 bbls
1029:4

Calculate the annulus volume. Casing size 5 9 5/8v 47 lb/ft.
1
ID 5 8.681v. Dual string completion 3/2v OD long string tubing.
2 7/8v OD short string tubing.
Dual packer at 7500 ft MD.
2 2 2
8:681 2 ð3:5 1 2:875 Þ
5 0:05327 bbls=ft
1029:4
7500 3 0:05327 5 399 bbls

1.1.9 Gas hydrates

A live well perforating operation was being conducted on a North Sea platform.
Wireline conveyed guns were used to open a new producing zone in an existing
gas well. After successfully perforating the new zone, the spent gun was being
pulled back towards surface. At the approximate depth of the seabed, the gun
became stuck. It was suspected that a hydrate was preventing further progress. The
wireline crew responded by pumping methanol into the tubing to disperse the
hydrate. However, a supervisor became impatient. To speed up the removal of the
hydrate, the platform production technicians were instructed to close the downhole
safety valve (located below the gun), and vent the tubing into the production
facilities. It was thought, by the supervisor, that reducingwell pressure would speed
up the removal of the hydrate. Soon after the tubing pressure had been lowered,
the wireline cable was observed to jump, followed by a complete loss of tension.
The loss of weight coincided with a rapid increase in wellhead pressure. The cable
was blown out of the well, and gas escaped through the grease head until the valves
on the Christmas tree were closed.
The subsequent investigation concluded that this sequence of events had
occurred.