Drilling

TVD vs. MD

Definition:

• TVD (True Vertical Depth): vertical distance from top to bottom.
• MD (Measured Depth): distance along the borehole.

Data Validation:

• TVD is always less than or equal to MD.

TOC, Lead and Tail Cement

Definition:

• After the cement job has been completed and slurry has entered the annulus, the top of the slurry column is called TOC (top of cement).
• If 2 different slurries is pumped in the cement columnn (different density / weight):
  • The slurry that is pumped first (and therefore enters the annulus first and will be on top in the annulus after the cement job has been completed) is called “Lead Cement”.
  • The slurry that is pumped after the “Lead Cement” (and therefore enters the annulus later and will be at the bottom in the annulus after the cement job has been completed) is called “Tail Cement”.

Data Validation:

• TOC always lies between casing shoe and casing hanger.

Drill String, Drill Pipe, BHA and Drill Bit

• Drill String:
• Drill Pipe:
• BHA (Bottom Hole Assembly):
• Drill Bit:

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