Engineering & Mining Journal

JUL 2018

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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SURFACE DRILLING JULY 2018 • E&MJ 53 www.e-mj.com cycle time by automating te- dious tasks and providing on- the-fly assessment of design standard compliance. In this process, standard analysis is complemented with modeling of the existing design. The re- sulting design concept is also analyzed with modeling. This may inform a second, fine tun- ing phase to examine multiple solutions. Modeling would then compare performance of the different concepts to identify the best solution. In the drafting step, the cutting structure design software feeds master models in 3D CAD to reduce drafting time and errors. Compressing the iterative cycle allows multiple analysis/ design iterations before a bit is manu- factured and field-tested, resulting in a faster development process and better initial performance. The design/model- ing process is guided by detailed perfor- mance calculations to reduce the total drilling cost (TDC). Focused on optimiz- ing drilling parameters, TDC calculations encourage efficiency and emphasize greater ROP. Virtual Drilling Replicating the interaction of the bit's cutting structure with the formation is much different than the more familiar modeling of cuttings removal using com- putational fluid dynamics calculations. Normally, cutting-structure evaluation must still be performed based on actual drilling and dull bit examination. Instead, AMP analysis specifically models the in- teraction of inserts and cone steel with the formation as the bit enters the rock, fractures it and creates a hole. The virtual drilling process starts with importing the 3D cutting structure from RC Pro software and creation of a scenar- io to replicate actual drilling conditions. The selected bit is run through the sce- nario and AMP records the forces as the bit interacts with the formation. Simulations correlate cone, insert, and bearing loads with observed dull bit modes and drilling conditions, while in- corporating drilling parameters (including RPM, weight on bit, mud density, hole depth and angle) and formation charac- teristics (such as compressive strength, ductility and abrasivity). The modeling output describes the pattern cut at the bottom of the hole, and the loading of critical bit compon- ents over time. Data output includes bit depth versus time, off-center force, and sliding, as well as load distribution by cone, row, cone steel versus insert, bear- ing load and torque. All this data is a huge resource that supplements the engineer's experience and knowledge. Through multiple charts and reports, the modeling data can be configured to compare various bits, or the same bit, in different drilling con- ditions. The engineer is supported with penetration rates and durability data, including gage rounding, cone erosion, broken inserts, and bearing failure, that contribute to the calculation of total drilling cost. The full analysis informs design de- cisions about insert selection and place- ment, bearings, and other bit features without resorting to the time and cost of field trials. In addition, modeling can assist field personnel in making bit selections based on bit type and operat- ing parameters. Field Examples In a Canadian diamond mine applica- tion, cutting-structure design software informed by modeling dramatically sped up the iterative process. The mine is inside the Arctic Circle, where sea- sonal ice road logistics dictate that a year's supply of bits is delivered during a short winter window. This constraint can significantly delay the iterative de- sign process. In Varel's initial work for the new customer, an existing 9 7/8-in. DF60 bit assembly was tested. Resulting dull bit modes were primarily bearing failure or coring due to broken spear points. The bits also showed flat crest- Figure 3—Modeling shifts the balance of the engineering effort to design and iterative frequency, and achieves benefits much faster. Figure 2—Virtual drilling speeds the iterative process with computerized design and analysis cycles.

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