Case Studies
Case 1: A Pilot Hole Gone Awry
A mining company wanted to put in a pipeline from a fluidized cement/backfill batch plant to an underground distribution chamber. This required drilling a pilot hole from the surface, along a predetermined path, to intersect with an underground distribution chamber. The pilot hole was to be driven at -53.3º slope and would be 380m (1244ft) long through native rock.
The Problem
The pilot hole had been drilled with an HQ diamond drill but had not come out where expected. Several directional tool companies surveyed the hole, but the results were contradictory.
The Icefield Tools Solution
Icefield Tools Corporation (ITC) was called in. The only available tool was a stock rental unit already consigned to and in the client’s offices. The ITC field technician retrieved the tool from the client and drove to the site.
The tool was pumped out through the bit on the end of 10m of aluminum extension rods. The driller started pulling the rods — as each 3m joint was broken, an instrument reading was taken. Eventually the driller started taking the readings himself. Once recovered, the tool was unscrewed from the extension rods and downloaded in the drill shack using a handheld computer. Within 10 minutes of recovery, the raw data were examined.
Some strange diagnostic readings were noted in the 30m of the borehole nearest the collar. When asked, the driller recalled that the hole was steel cased for this zone. These shots were edited out of the survey.
The resultant hole coordinates were in accord with the known constraints — the hole did not break out in the underground lunch room, main access drift, chamber or chamber cross cuts. The site geologist decided to drive a drift to the coordinates indicated by the tool. The hole was intersected.
Closure within 0.3%
Conventional underground survey instruments reported that the borehole intersection was 1.1m (3.6ft) from the location predicted by the Icefield tool. Over a 380m slant hole, this represents an error of 0.3%. A second pilot hole surveyed at a later date had similar closure.
Case 2: Surveying in Magnetic Ground
A diamond mining company required a reliable borehole trajectory tool to delineate their drill holes as built. The company required an accurate but simple-to-use tool that both drillers and geologists could operate.
The Problem
The ore contains magnetic minerals, which would affect the azimuth calculations. Conventional wisdom dictated that a magnetically-oriented tool could not be used.
The Icefield Tools Solution
The standard ITC tool was leased to the client with the understanding that azimuths calculated where the magnetic dip and/or the total magnetic field were outside the normal range might not be reliable (although dip readings would always be accurate).
By rejecting shots where the magnetic diagnostics indicated problems, favourable results were obtained. In several instances the hole trajectories were confirmed by later cross cut intersections. Because the MI3 tool records so many shots with little cost in time (usually one shot for every rod break), rejecting as many as two thirds of the shots still left more than enough shots to define the borehole trajectory.
