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Core orientation in vertical holes
Vertical hole in Portugal
• Ground investigation for mine shaft• 1250m deep (planned)• 5m radius• Drillcon drilling contractor• Devico
• Directional core drilling• Core orientation
Borehole specifications
• Core orientation required in project specifications
• Devico offered the DeviCore system, but mainly as a ”steering” tool to keep track of borehole inclination. Core orientation would be possible if inclination was above -88.5°.
DeviCore system
• Continuous orientation• Scratchers marks the core during drilling
• Single point orientation• The core is marked on surface after drilling
DeviCore principal
DeviCore 0° tool face aligned with master scratcher/mark
Drilling equipment
• Atlas Copco Corac N3/50 core barrel• 3m inner tube with split tubes• 50mm core
DeviCore in Corac
• Difficult to accommodate the DeviCore in the split tubes
• DeviCore takes up 1 meter of the inner tube
• Solution: 1.5m extension behind the inner tube/split tubes and on the core barrel
Core orientation
Mark on the inner tube corresponds with DeviCore
Core orientation cont.
• Drill 3m 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)
DeviCore 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 DeviDrill corrections
before 450m