Core orientation in vertical holes. Vertical hole in Portugal Ground investigation for mine shaft...

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