Below general good practice steps to avoid general drilling problems encountered during drilling operations
Inadvertent Side-tracking (in soft formation)
- Wash through obstruction without rotating with the drilling Bottom Hole Assemply BHA.
- Use bullnose (with centre jet plugged) on all hole opener and Underreamer runs.
- When reaming a dogleg, lower the Drill String at a rate greater than the Penetration Rate RPM at which the section was drilled.
Gumbo (sticky shale)
- Use seawater native clay mud for sticky formation.
- Control drill to at; 600 ft/hr.
- Maintain circulation velocity at 200 ft/min.
- If hole condition permits, drill the section with seawater and dump returns overboard.
- Maintain high annular velocity (+800 gpm for 12-1/4″ WBM hole and +1000 gpm for 12-1/4″ OBM hole sections).
- Control drilling to at; 600 ft/hr.
- Conduct frequent wiper trips (check also tripping pipe procedures).
- Space out Stabilisers every 5 – 10 stands in the Drill String.
- Pump in and out of hole – rotate if necessary.
- Use low rheology fluid.
Borehole Instability (brittle shale)
- Increase mud weight if possible.
- After drilling each stand, wipe the full Drill Pipe stand at least twice with pumps on. If wiping a full stand causes directional problems, wipe with 2 singles at least twice.
- Monitor drill cuttings for any sign of caving. If the cutting amount is suspicious, sweep hole with Hi-Vis pill and consider a wiper trip.
- Use non-Water Based Mud for brittle shale.
Lost Circulation (common in drilling carbonate formations)
- Control drill so as not to overload the annulus with cutting.
- Drill with maximum pump rate to clean the hole.
- Ensure lost circulation material is adequately stocked on board
- When sweeping hole with Hi-Vis pill, ensure the first pill is out of the hole prior to pumping another.
- Minimise the openhole expose times.
- Control the fluid loss from the drilling fluid to the formation.