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Coring Assemblies

This article describes the mains components of the coring assemblies: coring bits, core barels and drillstring.

Coring Bits

  • Coring Contractor shall provide a range of diamond coring heads.
  • The bit shall be run depending on the previous performance and grading.
  • Face discharge core heads shall be used in unconsolidated formations.

Core Barrels

  • The length of barrel to be run and the inner barrel requirements shall be based on coring success in offset wells and Petroleum Engineer requirements.
  • As few coring runs as possible shall be made and if possible all the core shall be cut in one run.
  • Core recovery is greater with a shorter core barrel and a shorter coring run.
  • Start cutting core with a 90 ft core barrel. If poor recovery is experienced, consider using a 10 ft core barrel.
  • The following shall be checked by the Coring Contractor and verified by the Drilling Supervisor:
    • The make up torque shall be in accordance with manufacturer’s figures.
    • The bearing assembly is free.
    • The inner barrel is straight with minimal corrosion on steel barrels.
    • The inner barrel space out is correct in accordance with manufacturer’s figures.
    • The barrel stabilisers are the correct gauge.
    • The safety joint is clean and properly lubricated.
    • The ball seat is compatible with the ball.

Drillstring

  • Drill collar weight shall be calculated to allow the maximum planned WOB plus 20 % extra. Alternately, the two collars above the jars shall be replaced by heavy weight drillpipe and these two collars place below the jars.
  • Drillpipe shall be drifted when pulling out the hole for coring to ensure that the ball shall pass through. New pipe added whilst coring shall also be drifted.
  • Full gauge stabilisers shall be run at 30 ft and 100 ft above the top core barrel stabiliser.
  • Jars shall always be run in the coring/drilling assemblies.