VOLUMETRIC WELL CONTROL
The volumetric method is mostly used in workover and production operations. It is a means of allowing the gas to migrate to surface under control. The gas needs to migrate at over (approx.) 1000′ per hour.
To allow the bubble to expand the casing pressure is held constant for a given volume of mud bled off. This operation is repeated, holding an ever increasing casing pressure until the gas reaches the surface (Holding Bottom Hole Pressure constant).
VOLUMETRIC METHOD APPLICATIONS
- A gas kick + migration + plugged drill string (only casing pressure can be read).
- No drill string in the well
- packer leaking
- wireline logging
- swabbed gas migrating.
EXAMPLE OF PLUGGED BIT
1- Calculate Safety margins and working margins
2- Allow the casing pressure to increase to 850 psi.
Note the time taken for this pressure increase then estimate percolating rate in ft/hr.
If Pressure increased by 150 psi in 15 minutes it means 600 psi/hr
3- When casing pressure is at 850 psi
- Bleed off at choke a volume of mud equal to the working pressure (50 psi).
- Hold Casing pressure constant at 850 psi during this operation.
- After 50 psi of mud equivalent has been bled off at choke allow the gas to migrate unexpanded until a further 50 psi of overbalance is attained.
- Bleed off 50 psi equivalent mud at choke and repeat procedure until gas is at choke.
- Four bleeds are shown. Depending upon the size of the volume bled and the well depth more or less
B- Open kill line stack valves.
C- Pump slowly into kill line.
D- Pump 3.6 bbls mud into annulus.
E- Allow the mud time to fall through the gas.
F- Bleed off pressure at the choke = the hydrostatic pressure of pumped mud.
Original Pit Volume = 120 bbls – Pit volume after kick and bleed = 152.1 bbls
5- Switch to Kill Mud
Now the well must be circulated to kill mud. This can be done by running wire line and perforating drill pipe or drill collars. If all the gas has been bled from the annulus then SICP can be used to calculate the kill mud.