With more than 25 years in the industry Devico has gathered extensive experience in directional drilling and borehole planning. Upon request Devico will, free of charge, analyze potential directional coring projects and give detailed borehole plans illustrating the potential savings.
Based on the target coordinates provided by the project geologists the Devico field engineer will propose a drill plan. In most mining projects the drilling will start with a vertical or an inclined hole, which is branched off towards several targets.
Kick-off requiring 50.12 m DCD
The drilling will be standard N-size wireline down to the proposed kick-off point, where DCD is initiated. DCD is performed until the borehole is aiming towards the final target, then the hole is finalized with N-size.
As the final section is short compared to the total borehole length, the probability of hitting the target accurately is significantly increased.
When the first target is reached the hole (the “mother hole”) can be sidetracked and aimed towards a second target. There are no limits on how many sidetracks can be made, but normally 5 to 10 branch holes are the most efficient.
6 mother holes with several branch holes each
When the first target is reached the borehole can be sidetracked and aimed towards a second target in three difference ways:
1. Cut the curve
3. Cement plug
“Cut the curve” means that the sidetracked borehole is cut straight out of an existing curve. The curve must be a DeviDrill section of the hole where the curvature has a dogleg of at least 8. The cut is performed with a regular core barrel, and is usually completed in 3-4 hours.
Wedging or setting cement plugs are methods used when the curvature is not sharp enough to cut. These methods are more time consuming and may take 1-2 shifts to complete.
With DCD, it is possible to increase the accuracy of a borehole significantly. Boreholes are always influenced by a natural deviation that, if not compensated for, will lead the borehole away from its intended target. The DeviDrill can steer a borehole in any given direction and bring it back to the planned path.
Shallow holes (500-700 meters) with limited natural deviation will usually hit the target with one DCD correction, while deeper holes may require a second or third correction as the hole progresses.
The target limits are specified by the project geologists, and may vary from project to project. The most common limits in the Devico projects are:
|500 to 1000||5-15 m|
|1000 m and deeper||10-25|