1. Field
The invention relates to earth drilling apparatus, and more particularly to coring devices.
2. State of the Art
Coring is a commonly used method for gaining information about the rock formations through which drilling is being performed. Apparatus for coring typically includes a cylindrical inner tube which is concentrically disposed within an outer core barrel. A coring bit at the distal end of the core barrel cuts a cylindrical core which is received in the inner tube. The outer core barrel rotates, but the inner tube does not. When coring in drill holes which are horizontal or highly deviated from the vertical, the inner tube may sag against the outer core barrel unless some means is provided for stabilizing the inner tube. Such sagging can cause drag against the rotating outer barrel, and consequent jamming of the core in the inner tube.
Previous devices for stabilizing the inner tube relative to the outer core barrel have typically comprised a bearing with rollers which surrounds the inner tube and fits between the inner tube and the core barrel. However, these have generally had very poor durability. The rollers tend to wear out, and the pins break prematurely, necessitating frequent replacement.
Accordingly, a need remains for a device to stabilize a nonrotating inner core tube with respect to an outer core barrel which is simple, inexpensive, and more durable than those described above.