DIVERTER PROCEDURE WHILE DRILLING ON A FIXED RIG
1. Where shallow casing strings or conductor pipe are set, fracture gradients will be low. It may be impossible to close the BOP on a shallow gas kick without breaking down the formation at the shoe. If a shallow gas kick is taken while drilling top hole then the kick should be diverted.
Drilling shallow sand too fast can result in large volumes of gas cut mud in the annulus and cause the well to flow, also fast drilling can load up the annulus increasing the mud density leading to lost circulation and if the level in annulus drops far enough then well may flow.
When drilling top hole a diverter should be installed and it is good practice to leave the diverter installed until 13 3/8" casing has been run.
2. If any indication of flow is observed while drilling top hole, close diverter immediately as the gas will reach surface in a very short time and it is inadvisable to attempt a flow check.
An automatic diverter system should first:-
a) Open an alternative flow path to overboard lines.
b) Close shaker valve and trip tank valve.
c) Close diverter annular around drill pipe.
d) If there are two overboard lines then the upwind valve should be manually closed.
Suggested diverting procedure in the event of a shallow gas kick.
a) Maintain maximum pump rate and commence pumping kill mud if available.
b) Space out so that the lower safety valve is above the drill floor.
c) With diverter line open close shaker valve and diverter packer.
d) Shut down all nonessential equipment, if there is an indication of gas on rig floor or cellar area then activate deluge systems.
e) On jack-up and platform rigs monitor sea for evidence of gas breaking out around conductor.
f) If mud reserves run out then continue pumping with sea-water.
g) While drilling top hole a float should be run. This will prevent gas entering drill string if a kick is taken while making a connection. It will also stop backflow through the drill string on connections.