Boart Longyear's Drilling Services Division (CDD) at work at Anglo plc's Black Mountain Mine – Aggeneys.

Situation:

Anglo plc's Black Mountain copper, nickel and zinc mine in Aggeneys is under pressure to prove a new ore body and design a mine before its existing Broken Hill mine runs out of ore in 2003.

Challenges:

Phases 1 and 2 to evaluate the ore body, then the Shaft Hole Phase of the project, were all characterized by:

* Exploration drill holes up to 1 850m
* Difficult in-hole conditions
* Tight time constraints
* Previously drilled 3km x 400m grid that had "drifted"

Solution:

With a prevailing pattern of broken schist, gneiss, quartzites and ore body formations - and the consequent risk of frequent deviation - there was a requirement for efficient, accurate and price-competitive shallow-hole drilling using advanced drilling equipment and state-of-the-art surveying, wedging and steering techniques. Based on its widespread experience and success on similar surface drilling projects in southern Africa the 18-month contract was awarded to Boart Longyear's Drilling Services Division (CDD). Work was completed at the end of 2000.

Method:

Phases 1 & 2
Using a variety of drilling rigs, rods and bits manufactured by Boart Longyear group companies around the globe, the CDD evaluated the ore body by drilling intersecting holes at locations predetermined by the mine in between the southerly-drifting grid holes previously completed. Three LY44s (rated to 1 400m), two LY50s (rated to 1 850m), a LF70 (rated to 700m NQ), a truck-mounted LY38 (rated to 650m) and two SECO L3000s (rated to 5 000m) were selected to drill a total of 13 holes to a cumulative depth of 24 800m. Ranging between 1 300m and 1 850m in depth, they completed three 600m+ deflections and 137 directional, non-directional and retractable wedges to direct the holes and used Reflex Ez-Shot single shot and Sperry Sun multi-shot survey equipment at 24-hour intervals to provide up-to-the minute electronic readouts.

Shaft Hole Phase
The challenge here was to drill a 1750m hole with a deviation constrain of not more than 2 degrees. The hole had to be HQ size, but conventional HQ rods are only rated to 1200m.

Not only was the HQ equipment not entirely suited to the task but time constraints prohibited the use of a TNW corebarrel and conventional drilling techniques, so CDD elected to use a 35-ton jack-knife derrick, an L3000 (capable of drilling 5 000m), and a 63mm HQ wireline drill fitted with Boart Longyear's new HRQ high performance rods. The hole proceeded as planned but a running dyke was intersected at 865m, Boart Longyear's experienced team overcame the difficulty by introducing a specific mud system to stabilize the dyke against caving and collapse. The HRQ rods cam under terrific pressure to perform in these nearly impossible in-hole conditions and they came through with flying colours, ensuring the job was completed on time.

Pivotal to the success of Boart Longyear Drilling Services Division's surface drilling contract at Black Mountain were the company's new HRQHP wireline drill rods, attests [title] Malcolm Smith. They also provided the first opportunity to test the Canadian-developed product in South Africa and, as this Case Study indicates, the Chromium Molybdenum steel rods were put rigorously through their paces. Standard HQ rods, though rated to X, tend to pull apart after 600m, says Smith, and were ill-equipped to complete the shaft hole at Black Mountain, even without taking the severe in-hole conditions into account. HRQHP rods are rated to 2000m and have a multitude of superior features: Low stress thread design for added joint strength and efficiency, that virtually eliminates belling and bulging

Through-wall quench and temper heat-treated box and pin ends for greater strength on the tool joint where it is most needed, as well as increased depth capacity and rod life

Maximum wear resistance and increased thread life through a unique induction surface hardening process

Light bit weight pressures that minimize deviation and improve bit life

Reduced fuel costs

Quicker tripping times

Nonetheless, fragmented rock formations at Black Mountain, combined with the running dyke encounter and deviations that necessitated 23 wedges all severely tested the capability of the high performance rods. Yet post-contract examination revealed that the rod string suffered no fatigue or mechanical damage, mirroring results achieved elsewhere in the world. "It's good news for geologists", says Smith, " who can now expect a bigger and better core sample at a reduced cost."