Removal of Core Barrel from the Hole

After the core has been collected, the core barrel is retracted a short distance (several inches) to break off the core. If standard coring rods and core barrel are used in the coring operation, the rods are tripped out of the hole and the core barrel is dismantled in much the same manner as described in a later section, "Removal of rock core from the inner tube."

The wireline system of coring provides the advantages of not having to trip the coring rods out of the hole after each core run is completed resulting in improved hole stabilization. This hole stability is an important aspect in the hydraulic-rotary coring of unconsolidated materials; therefore, the wireline system of coring is the principal system that the Water-Resources Division uses. When the wire-line coring system and overshot assembly is used (fig. 21), it is run down the inside of the coring rod on a i^-in. cable, spooled from the wire-line winch. When the overshot assembly reaches the inner-barrel head assembly, the overshot latching assembly engages the inner-barrel spearhead, and the inner-barrel assembly is hoisted to the surface. After the innerbarrel assembly has been removed from the drill rod, another complete inner-barrel assembly is dropped down the drill rod and allowed to settle through the drilling mud or is slowly pumped down to bottom and coring can be resumed. This removal procedure is followed for each core interval.

  • Wireline drill rod
  • Overshot
  • Overshot jaws latching spring
  • Ovtrahot IstchnQ ntcfflUy (latches over innĀ«r-baml spearhead)
  • Wiralina core-barrel assembly connecting adaptor
  • Inner barrel spearhead (connected to innerbarrel head assembly)
  • Spring latch

Figure 21 .-Wire-line overshot assembly in locked position on inner-barrel head assembly.

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