|New Mexico Supercomputing Challenge|
Challenge Team Interim Report
Sandia National Laboratories has been doing research on the development of Polycrystalline Diamond Compact (PDC) bits for several years now. They are developing and testing these bits primarily for geothermal drilling applications, yet the technology will be of benefit to oil and gas drilling as well. PDC bits are currently used extensively in the petroleum industry in soft and medium-hard rock formations but have yet to be repeatedly used for geothermal drilling.
The reason Sandia Labs is developing PDC bits for hard-rock drilling is the bits currently used, roller cone or tri-cone bits, don't last long in high-temperature, hard-rock drilling environments. These roller bits are expensive and drill very slowly in hard-rock formations. The roller bit has many faults due to the moving parts on it. The elastomeric seals that seal the roller cones lose their effectiveness when they are exposed to extreme temperatures from the abrasive drilling fluid. The bits also handle frictional temperatures very poorly. This leads to the need to frequently replace the bit, which gets extremely expensive.
Sandia Labs believes improving PDC bit technology will help the drilling community in general drill better at a much lower cost. The PDC bit is made up of synthetic-diamond cutters that are attached to a solid bit head. The bits and the cutters are designed to handle very high temperatures and stresses. The bits come in different shapes and sizes. The Labs are now experimenting with the bits trying to find the optimum placement of the cutters for best bit performance.
The Polycrystalline Diamond Compact is what makes the bit work. The PDC cutter consists of a thin layer of polycrystalline diamond. The artificial diamond provides the cutter with the type of resistance needed for drilling hard rock. The diamond is bonded on the front of a tungsten carbide stud. This is the basic cutter. The "PDC matrix bit" has the cutters directly brazed into the bit body. Alternatively, "PDC steel bits" use PDCs mounted on studs that are pressed into holes in the bit body. Because of the artificial diamond compact used in the bits these bits are very expensive, but they can drill faster leading to an overall decrease in total expenses if properly used.
The Labs became interested in PDC bit designs because of the fact that there were no moving parts on these bits. The Labs have found the bits to be as fast or faster than the roller bits. Technology improvements are still needed before they can be used effectively for drilling hard rock. They are researching the bits further and have found a few limitations and are working on fixing them. With this new technology, Sandia Labs hopes to improve the efficiency of the drill bits we use for earth-boring drilling. This new type of bit should benefit the earth-boring drilling industry immensely.
What is needed in current PDC bit technology is a predictive drilling costs model which guides the industry in how to best use PDC bits to maximize the rate of penetration and bit life subject to a given set of drilling requirements. Such a model could be used to set the operating conditions for the bit to reduce the overall cost of a drilling project. Additionally, the dependence of overall drilling costs on PDC bit drilling parameters is not well characterized. Such a predictive model could also be used to discern the best approach to using PDC bits for hard-rock drilling.
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