Curved Drillhole From Target

On the Drillhole | Planning tab, in the Planning group, click From Target (Curved) to specify a target location and then build a trace string towards the collar.

A drillhole design in which the direction of the drillhole string is opposite to the drilling direction, running from the target to the collar, is a From Target design.

A from-target design is typically used when the target location is known and the collar location is to be determined. For surface drilling this method optionally includes automatic clipping to a surface DTM, automatic reversal of the drillhole string, and automatic extension beyond the target.

From target-design supports straight or curved up-holesHoles in which the drilling direction is inclined upwards or down-holesHoles in which the drilling direction is inclined downwards..

Micromine uses the segment length to control the length of each string segment that represents a curved hole. When the strings are converted to collar and survey files, the segment length also determines the interval between successive downhole surveys.

The safest way to plan a curved hole is to start by interactively adding segments until the hole is the right length. You can then design other holes using total length once you get a feel for how they relate to your project area.

To interactively add segments to a curved trace string, starting at a defined target location:

If a compatible layer is not open, or is not the active layer, you will be prompted to create or select an active layer:

Digitise a point as the target location and then right-click to bring up the Plan Drillhole from Target (curved) form.

Specify the segment length and the length, orientation, and deviation of the hole.

Segment length

Enter a segment length (in grid units).

Initial Orientation (in Drilling Direction)

Enter an Azimuth and an Inclination for the initial segment of the trace. The segments you add will deviate from this start orientation.

Regardless of the design direction (from collar or from target), Micromine always expects the orientations and deviations to be specified in the drilling directionDrilling direction is the direction in which drilling will proceed, always running from the collar towards the target. Note that the drilling direction may be inclined downward (for surface and underground holes) or upward (for underground holes)., not the design direction.

For example, if you are designing a from-target hole, which will be drilled at -60° towards the east (090°), then you should enter an inclination of -60 and an azimuth of 90, even though you are designing the hole upwards from the target. Micromine will automatically reverse the directions and deviations for you.

The drilling direction and design direction are independent variables.

Rate of Deviation

The segments that you add to the string will deviate in their orientation, over a specified segment length and by a specified Azimuth deviation and Inclination deviation, measured in degrees per segment. Deviations are defined in terms of the drilling direction.

Use the rate of deviation options with care. Drillhole deviation is the result of a complex interaction between the drilling parameters (bit type, feed pressure, rotation speed etc.), the cutting or hammering action of the bit, the rocks through which the hole passes, and the angle between the drill bit and the fabric of the country rock. Changing any one of these parameters may result in significantly different rates of deviation compared to other holes.

In a new project area you should plan for straight holes until you have enough drilling to understand how the prior holes deviated. Even with this knowledge you should always consider any planned deviation to be an approximation of the completed drillhole.

Drillhole Length

Interactive

Select this option to adjust the length of the hole interactively rather than specify a total length or calculate the length based on the number of segments.

Number of segments

Multiple segments can be added using the same orientation or the same deviation specified in the form. Enter the number of segments to create.

Extend to DTM

Alternatively, specify the Type and Name of a DTM to snap to. The point at which the DTM is pierced by the trace string will determine the length of the hole.

Finalise Hole (on Finalise)

If selected, the following options will determine what happens when you click the Finalise button and close the form:

• Reverse string has the effect of making the first point of the string the collar.
• Extend Beyond Target will lengthen the hole by a specified total length. A preview line for the extension is shown in the display:

Add Segment(s)

Click the Add Segment(s) button to add one or more segments of the specified length and orientation.

Undo

Click Undo to undo one or more of the segments you have added.

Finalise

See "Finalise Hole" above.

Cancel

Click Cancel to close the form without finalising the hole.

Forms

Click the Forms button to select and open a saved form set, or if a form set has been loaded, save the current form set.