Realistic Simulation Accelerates Safety Evaluation Of Mine Designs

Mining company achieves significant productivity gains with 3-D mine models developed with finite element analysis software.

In what has been described as a step change beyond traditional processes, Abaqus finite element analysis (FEA) software from SIMULIA (the Dassault Systèmes’ brand for realistic simulation), is being used to enhance mine design and engineering simulation at a number of major mines around the world. In North and South America, Africa and Australia some of the world’s biggest mining companies are applying FEA technology to evaluate safety and improve design planning, implementation, and operations.

Beck Arndt Engineering (BAE), a Sydney, Australia-based international consultancy, is a pioneer in the commercial development of engineering solutions for the mining industry. The consultancy has worked closely with engineers at SIMULIA Australia to expand the use of Abaqus FEA simulation software for mining applications.

Among the early adopters of mine-ready FEA technology is the world’s largest miner, BHP Billiton. With BAE’s help, BHP has already applied this technology to evaluate mines in Canada and Australia. At the BHP Billiton Nickel West Perserverance Deeps project in Western Australia, Abaqus FEA software is now being used to help engineer the safety and productivity of planned deep-mining operations.

To achieve this goal in the deep-mining environment requires significant technological innovation. Using measurements of site deformation and seismicity, Abaqus FEA models have been calibrated and, in a single day, used to simulate a full, three dimensional, inelastic analysis of a mine’s life cycle.

In recent years, similar applications at Debswana’s Jwaneng mine in Botswana, the Newcrest Mining Ridgeway Deeps project in New South Wales, Australia, and Rio Tinto’s Argyle Diamond mine in Western Australia have also established Abaqus FEA analysis as the leading technology for multi-scale, simulation-aided mining engineering.

Dr. Joop Nagtegaal, a pioneer of FEA and a Dassault Systèmes Corporate Fellow, says that Abaqus FEA software is unique in its capabilities to enable mining engineers to investigate design innovations from the drawing board to full production. “In the design stage, Abaqus models, which include rock mass volumes spanning several kilometers around the orebody and down to excavations just a few meters across, are used to compare and optimize engineering options,” he said. “Then, as the mine goes into production, large volumes of data from the field are incorporated with the analysis models to allow them to be calibrated to a precision not previously available to the mining industry.”

Seismic event forecasting has become increasingly important at several sites where mining-induced seismicity is a concern. Dr. Stephan Arndt, principal engineer at the BAE Perth office, said the vast amount of analysis required to create solutions in today’s competitive mining markets requires new technologies and methods.

One innovation has been the development of the Dissipated Plastic Energy (DPE) analysis method. DPE analysis has been used to develop controls for potential problems, as well as to better understand how rock masses are damaged. (See Figure 1).

As the size and complexity of mining problems being studied increase, engineers are facing the need to leverage high-performance computing solutions.

“The size of the models we now use in mining is unprecedented,” said Arndt. “Distributed Memory Parallel (DMP) processing, using 32 CPUs with Abaqus FEA software, gives us the capacity to compare a number of different scenarios for mine-scale model simulations in a very short time. The level of detail achieved in these models allows us to calibrate deformation and rock mass damage, seismogenic potential and ground support performance. Abaqus has an important role to play in mining and our analysis methods are setting new standards in this industry.”

Another application of nonlinear modeling is the design of ground support. Similar to applications in tunneling and civil engineering, mine excavations are subject to high deformation. (See Figure 4). Not so typical are the strains and loads involved. In some mining cases, tunnels must survive in very weak rock a very short distance from massive underground excavations at great depth.

“To ensure the safety of people and to achieve productivity objectives on these challenging sites with unique geological characteristics, mining engineers need to think outside the box,” said Arndt. “This technology enables quick, cost-efficient analyses, which in turn facilitate the logical decision-making process necessary for the future development of mines in safe, environmentally-sound and more economical ways.”

“Acceptance of FEA technology in mining is similar to the automotive industry experience, in which Abaqus has been accepted as a part of the vehicle body design process,” said Dr. Nagtegaal. “Auto makers have learned that performing crash simulations of their designs with FEA software is much less costly than real life barrier smashes, and provides a better platform for developing ‘what if’ scenarios.

“Today, we are integrating Abaqus as a tool for simulation-aided mining engineering in much the same way, with similar achievements in cost saving and improved safety.

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Smarter, Faster Drilling

The future of mineral exploration looks brighter thanks to the application of a proven oil industry technique

Providing geological and geotechnical data and related information for resource evaluation and mine development through drilling and downhole geophysical logging is an essential primary objective for all exploration and mining companies.

Yet these processes are also two of the greatest drains on a company’s resources—drilling accounting for roughly 25% to 65% of total exploration costs and some 5% to 15% of total mining costs. In a high-risk industry, these are two fundamental areas where scientific solutions are needed immediately.

Down-Hole Solution

One such solution is being introduced courtesy of the oil exploration industry. In recent years a technique called “Logging While-Drilling,” or LWD, has been used extensively in oil exploration to describe the petrophysical characteristics of the rock mass surrounding a borehole.

It is now recognized that LWD has the potential to be more widely adopted by the minerals exploration and wider mining industry to boost efficiency and cut costs. Whereas geophysical logging traditionally occurs after a borehole has been drilled, this invariably introduces delays between drilling and interpretation, and requires the mobilization of additional personnel and equipment. It can also prompt production losses and delays and has the potential to cause the loss of information due to postdrilling borehole collapse and blockages.

All of these factors can result in additional costs that could be reduced by replacing the two-stage process of drilling and geophysical logging by logging that is carried out while drilling, using high-speed and robust data acquisition sensors.

Technology Integration

To realize the full potential of geophysical logging, data acquisition should ideally be integrated with drilling, according to CSIRO Exploration & Mining’s Principal Researcher Dr. Binzhong Zhou and Research Leader Dr. Paul Degnan.

“Since the post-1986 oil-crisis, the impetus for more cost-effective technology has made LWD instruments for continuous formation evaluation widely available in the petroleum industry,” they announced in a paper presented in October at the Drilling for Geology 2008 conference in Brisbane. “LWD in the oil industry can now provide all the measurements that were traditionally acquired through wireline logging, including electrical, electromagnetic, acoustic, and nuclear logging parameters and images, which can be used for rock type identifi cation and correlation, rock mass characterization, litho-stratigraphic interpretation, orebody delineation and grade estimation. 

“LWD (and the associated methods of ‘measurement-while-drilling’, or MWD, which use sensors and other tools to monitor the drilling process itself) are techniques that have the potential to be introduced into the hard rock mining industry in Australia. They can also be applied in the coal mining industry where there is a requirement for geo-steering for drilling horizontal gas drainage holes within coal seams associated with gassy and outburst coal mines.”

Catching On

 

The researchers said that although a lack of impetus within the hard rock mining and coal industries previously impeded the application of LWD into those sectors, there is now a growing recognition of the value of this technology. Adapting LWD/MWD systems for use in minerals exploration and mining is still in the research stage with no commercial system developed so far.

The main reason adoption has not progressed is because of the significant costs involved in adapting and making the technology more widely available, but now that the oil industry has overcome many of the technical issues associated with slimhole LWD, it may motivate the mining industry to adopt the LWD and MWD techniques.

LWD has the following potential benefits to the mining industry, although because the technology is in its early stages of development they are yet to be realized:

  • Real-time evaluation of rock mass properties, lithology and grade—without the need for coring
  • Improved blast design, fragmentation and recovery
  • Ability to increase distances between sublevels
  • Data guarantee even if the hole is lost
  • Unobtrusive and cost effective integration of logging with drill operations
  • Early indications of ore, geotechnically weak zones and other zones of interest
  • Improved sampling of coal and ore bodies when combined with steerable drills

Crossover Technologies

According to Drs. Zhou and Degnan, perhaps the most important development of LWD equipment that will benefi t the mining industry in the long-term is the conjunctive adoption of slimhole drilling technology. Slimhole is one of the most cost-effective methods of oil and gas reserve development. It involves drilling smaller diameter holes (as narrow as 69.85 mm) and using small diameter production casing and tubing. “The use of a small-diameter well-bore reduces the overall cost of exploration drilling and reserve development through more rapid drilling, reduced energy and drilling mud consumption and the use of smaller surface casing and conductor sizes,” they explained.

The Drilling Engineering Association undertook a special project to develop and evaluate coiled-tubing and slimhole technology (through Maurer Engineering Inc. in 1995).

A decade later, the U.S. Department of Energy partnered with industry to initiate the Microhole Technology Program to develop a suite of technologies that would enable the drilling of wells with casings less than 114.3 mm in diameter using coiled tubing drill rigs that are relatively small and easily mobilised. This development has driven research which is allowing LWD/MWD tools to shrink in size to fit small diameter holes.

“It is evident that the LWD devices developed for slim/micro boreholes in the petroleum industry can be adapted to existing HQ (~96 mm diameter) or NQ (~76 mm diameter) drill strings commonly used in the mining industry,” said Drs. Zhou and Degnan.

“CSIRO is currently carrying out preliminary research that will one day permit the mining industry to adopt slimhole and micro-hole drilling technology using coiled tubing along with its associated LWD technologies. “All these developments indicate that the time is coming for the mining industry to adopt these new technologies for mining applications”

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Reprinted with permission from CSIRO Earthmatters, Issue 18, November/December 2008.

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