Functions and Components of a Drillstring in Oil Drilling

Functions of the Drillstring:

• Transmits rotation to the drillbit
• Exerts weight on the bit; the compressive force necessary to break the rock
• Guides and controls the trajectory of the bit
• Allows fluid circulation for cooling and cleaning

Components of the Drillstring:

• Drillpipe
• Drillcollars
• Accessories including:

• Heavy-walled drillpipe (HWDP)
• Stabilisers
• Reamers
• Directional control equipment

The Kelly:

• Transmits rotation and weight-on-bit to the drillbit
• Supports the weight of the drillstring
• Connects the swivel to the uppermost length of drillpipe
• Transmits drilling fluid from the swivel into the drill string

The Top Drive:

A combined rotary table and Kelly mounted on the rig's swivel, assisting in pipe handling during operations.

Drilling Problems:

• Pipe Sticking
• Lost Circulation
• Hole Deviation
• Pipe Failures
• Borehole Instability
• Mud Contamination
• Formation Damage
• Hole Cleaning

Mechanical Sticking Causes:

• Hole pack off or bridging
• Settled Cuttings
• Shale Instability
• Fractured Rocks
• Key Seating
• Undergauge Hole

Total Losses:

• Maintain proper mud weight
• Minimize annular friction pressure
• Maintain adequate hole cleaning
• Set casing to protect weaker formations
• Treat mud with lost circulation materials if anticipated

If Losses Occur:

• Pump lost circulation materials in the mud
• Seal the zone with cement or other blockers
• Set casing Dry drill (clear water)