Sample core drilling unit has outer barrel with drill bit - rotatably contg. inner barrel with core catcher axially movable against spring

摘要

The core drilling unit (1) comprises an outer core barrel (5), which is secured at the lower end of a drilling string and, at its lower end, carries (4) a core drill head (2,3), and an inner core barrel (17) which is rotatably carried (via 13-16) by a swivel (9;10-12) and, at its lower end, carries (22) a core catcher (23). The lower end (24) of this core catcher extends by a small amount below the level (H) at which the annular downward mud passage (26) around the catcher enters a portion (29) with reduced cross-sectional flow area. The inner core barrel is axially movable relative to the outer barrel against spring force (upward to H against spring 31 and possibly downward to L against spring 32). Used as drilling unit to take core samples (35) in underground formation (33). The arrangement gives clear indication if, e.g. through fracture of the core, this can no longer move upwards in the inner barrel, as the catcher is raised (H) and the mud pressure suddenly drops by the flow constriction (29) being eliminated. Drilling is then stopped and damage to the core and to the inner barrel (if in plastic) prevented.