Engineering & Mining Journal

JUL 2014

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scheduled for production next year. And, of course, Newcrest now has the in-house expertise to be able to evaluate other deposits for block caving, including its huge Wafi-Golpu prospect in Papua-New Guinea. Hydraulic Fracturing Helps Fragmentation With near-surface opportunities for block caving becoming fewer, more recent devel- opments are commonly encountering new challenges in terms of natural orebody caveability. Deeper rocks are stronger, less fractured and so less amenable to caving on their own—hence the need to give nature a helping hand. Hydraulic fracturing offers a means of doing so, effectively preconditioning the orebody by enhancing existing weaknesses while creating others. Stephen Miko from the Canadian equipment manufacturer, ConMico, said, "Caveability can be en- hanced by drilling the orebody in a pre- determined pattern to a depth of up to 150 m, inserting a high-pressure packer and hydro-fracturing in 1- to 1.5-m seg- ments for the total length of the hole. As well as pre-conditioning the orebody, the fractured area is de-stressed, making it much more predictable as to how the ore- body will cave." ConMico has developed a 400-hp portable high-pressure hydraulic fracturing rig that is completely self-contained apart from power and water supplies. Supplied to Codelco for use mainly at El Teniente, but also at its other block-cave mines, the rig is just more than 4 m long and 2.5 m high, making it very maneuverable, ConMico noted. Once started, Miko said, the system inflates the packer's tubular rings to about 12,000 psi to hold it in place in the hole, then applies water at pressures of 4,000- 8,000 psi to fracture the rock. Fracturing begins at the back of the hole, with the packer being moved toward the collar, sec- tion-by-section, until the entire hole length within the ore zone has been treated. Working at such pressures, the packers themselves are fairly sophisticated pieces of equipment, according to the commercial director for Australian-based Inflatable Packers International (IPI), Howard Kenworthy. "Twin packer ('straddle') systems that inflate to isolate the section to be hydraulically fractured work at up to 10,000 psi (690 bar), sometimes greater," he said. "Operating protocols vary by mining company, but typically the packer inflation is via the same pump and an independent high pressure hose, with the high- flow/high-pressure injection through the sealed rods that have the straddle packers on the end—working either 'up hole' or 'down hole.' Controls ensure that the pack- ers are inflated to a higher pressure than the injection pressure for safety purposes," he added. According to Kenworthy, only pure water is injected, which typically fractures a radius of 25 m around the hole. "The holes themselves are normally 96 mm diameter, although one mine is trialing 76- mm holes with a 750-mm separation between packer positions," he said. IPI's principal product for hydraulic fracturing in block caving, the DuraFRAC HPC packer, is available for standard NQ (76 mm) and HQ (96 mm) hole sizes. The company claims that these packers are exceptionally durable, and can be used in JULY 2014 • E&MJ; 35 www.e-mj.com B LO C K C A V I N G EMJ_pg32-37_EMJ_pg32-37 7/2/14 8:35 AM Page 35

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