Gas lubrication is the process of removing gas from beneath the BOP stack while maintaining constant bottom hole pressure. Lubrication is best suited for surface stacks, but the dynamic gas lubrication procedure can be used to vent gas from beneath a subsea stack.

Lubrication can be used to reduce pressures or to remove gas from beneath a surface stack prior to stripping or after implementing the Volumetric Procedure for controlling gas migration. The volume of mud lubricated into the well must be accurately measured.

Gas lubrication volume method

English units

Procedure:

1. Select a range of working pressure, Pw. Recommended Pw = 100 200psi.

2. Calculate the hydrostatic pressure increase in the upper annulus per bbl of lube mud:

   
   

3. Pump lube mud through the kill line to increase the casing pressure by the working pressure range, Pw.

4. Measure the trip tank and calculate the hydrostatic pressure increase of the mud lubricated for this cycle.

5. Wait 10 to 30 minutes for the mud to lubricate through the gas.

6. Bleed dry gas from the choke to reduce the casing pressure by the hydrostatic pressure increase plus the working pressure range.

7. Repeat steps 3 through 6 until lubrication is complete.

Metric units

Procedure:

1. Select a working pressure range, Pw. Recommended Pw = 700 1400kPa.

2. Calculate the hydrostatic pressure increase in the upper annulus per m ³ of lube mud:

   
   

3. Pump lube mud through kill line to increase casing pressure by working pressure range, Pw.