Core orientation in vertical holes Vertical hole in

Core orientation in vertical holes

Vertical hole in Portugal • • • Ground investigation for mine shaft 1250 m deep (planned) 5 m radius Drillcon drilling contractor Devico • Directional core drilling • Core orientation

Borehole specifications • Core orientation required in project specifications • Devico offered the Devi. Core system, but mainly as a ”steering” tool to keep track of borehole inclination. Core orientation would be possible if inclination was above -88. 5°.

Devi. Core system • Continuous orientation • Scratchers marks the core during drilling • Single point orientation • The core is marked on surface after drilling

Devi. Core principal Devi. Core 0° tool face aligned with master scratcher/mark

Drilling equipment • Atlas Copco Corac N 3/50 core barrel • 3 m inner tube with split tubes • 50 mm core

Devi. Core in Corac • Difficult to accommodate the Devi. Core in the split tubes • Devi. Core takes up 1 meter of the inner tube • Solution: 1. 5 m extension behind the inner tube/split tubes and on the core barrel

Core orientation Mark on the inner tube corresponds with Devi. Core

Core orientation cont. • Drill 3 m as normal • Reduce or remove water flow • Instrument reading before breaking the core

Core orientation cont. Mark the core at 0° tool face and pump the split tubes

Core orientation cont. Mark the core according to tool face reading (shows up)

Devi. Core results • Core orientation has worked (surprisingly) well • Good results achieved even at inclinations down to 89. 3° • Normal error 0°-10° • Maximum error about 30°-40° • All orientation work performed by the drillers

Understanding the orientation • Some issues getting the core loggers to understand the orientation • Making the orientation line from the reference mark • Vertical hole gives rapid changes in azimuth which moves the orientation line over the rock structures

Directional core drilling • High natural deviation • Soft and fractured rocks • Dogleg setting of 6!! • 5 Devi. Drill corrections before 450 m