Locking means for facilitating measurements while coring

Abstract

In accordance with the present invention, rotation of the inner barrel relative of the axis of symmetry of the core barrel (indicative of core twist-off or core sand erosion during coring operations) is detected by a novel sensor combination comprising a Hall-effect device imbedded in a support sleeve of a custom safety sub attached to the outer core barrel adjacent to a single signature magnet fitted to and carried by a special support ring attached to the inner barrel. In releasably attaching the inner and outer core barrels together, the special support ring is made to be locking through operation of a series of compression strings acting between the lower surface of the ring and the inner core barrel as to wedge the upper surface of the support ring against an annular stopper ring. Result: the inner core barrel does not rotate relative to the outer core barrel during the trip down to the bottom of the well bore. Before coring commences, the Hall-effect device can be pretested since the signature magnet is locked in circumferential side-by-side relationship with and hence detectable by the Hall-effect device. Increases in mud pressure at the core site, causes release of the support ring (and the magnet) relative to the outer core barrel.