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Technology News 392 - abandoned mine lands program TN #6: the use of polyethylene oxide to improve drilling system performance.

Minneapolis, MN: U.S. Department of the Interior, Bureau of Mines, TN 392, 1991 Oct; :1-4
Objective: To develop a cost-effective tool for improving the performance of rock drilling systems used in detecting and delineating underground mine voids and for coal exploration. Approach: To investigate admixtures of polyethylene oxide (PEO) at zero surface charge (ZSC) concentrations as drilling fluid additives to enhance penetration rates and extend bit life in rock drilling systems. Background: Bureau researchers have investigated the use of chemical additives to enhance drilling performance and found that the most efficient drilling occurred when the drilling fluid was able to maintain a zero surface charge on the surface of the rock being drilled. Laboratory drilling studies have been performed on rock types such as quartzite, granite, taconite, and marble. The lab tests were conducted using 5/8-inch diameter diamond-impregnated coring bits with cationic compounds as the surface charge neutralizing additives. These studies demonstrated enhanced drilling performance, however, only at the singular additive concentration that produced the ZSC condition. A breakthrough was made when Bureau researchers found that polyethylene oxide, although a nonionic polymer, was able to maintain the ZSC condition over a wide range of concentrations. Success using polyethylene oxide as a drilling fluid additive during laboratory tests and subsequent field tests on hard rocks prompted testing of PEO on softer rocks. The Bureau recently tested PEO as a drilling fluid additive in drilling coal measure rocks to detect and delineate underground mine voids on Abandoned Mine Lands (AML). How It Works: The mechanism underlying the enhanced drilling performance is hypothesized to be activated cracking. Scientists know that the rock surface is under maximum tension when under zero surface charge conditions. Under these conditions, the likelihood of increased crack formation at or near the rock surface is increased since the rock surface is weakened under tension. When the increased density of cracks is propagated, faster rock breakage occurs and results in faster drilling penetration rates. Less bit wear is also observed. The wear force on the bit is lessened, since a rock surface with a higher density of cracks provides less resistance to the advancing bit than a rock surface with a lower density of cracks. The activated cracking hypothesis has been validated by Bureau researchers in the drilling of transparent, synthetic quartz with water alone and with ZSC concentration solutions of PEO and other chemical additives. High speed photography of synthetic quartz drilling showed a zone of cracking in front of the advancing bit when drilling with ZSC concentration solutions of PEO and each of the chemical additives tested. This cracking did not occur when drilling with water alone. To best take advantage of this chemically-induced rock weakening, users need to ensure that the mechanical energy introduced for drilling is not so high that it overrides the chemically-induced cracking effect. Less rotational speed and/or thrust may be necessary when using the PEO additive. Field Test Results: In a controlled field test in Ohio, conducted in cooperation with a coal exploration drilling program, NQ-size (311) coreholes were drilled alternately in coal measure rocks with water alone and 15 ppm (ZSC concentration) solutions of PEO in a side-by-side pattern to depths ranging from 55 ft to over 170 ft. Penetration rate increases of 39.4, 27.3 and 22.1 pct were obtained for shallow, medium-deep, and deep holes, respectively, drilled with PEO solutions compared to water alone. Comparing similar lithologies in these holes, average penetration rate increases of 24.0, 26.2, 27.8 and 40.8 pct were obtained for limestone, shale, carbonaceous shale, and claystone, respectively. In a controlled test in Pennsylvania, concluded in cooperation with the Pennsylvania Department of Natural Resources' drilling program to determine the extent of a fire in an abandoned underground mine, NQ-size (311) coreholes were drilled alternately in coal measure rocks with water alone and 15 ppm (ZSC concentration) solutions of PEO in a side-by-side pattern to depths ranging from 30 to 100 feet. Comparison of drilling performance for similar lithologies in these holes yielded average penetration rate increases of 14.8, 35.1, 47.1, and 49.3 pct, respectively, for highly fractured claystone, fractured claystone, fractured claystone with interbedded sandstone, and unfractured claystone. Health, Safety, and Environmental Considerations: Polyethylene oxide (PEO) is a non-toxic, high-molecular weight, nonionic polymer. The U.S. Environmental Protection Agency has given approval to a wide variety of applications of PEO in solution including in agriculture as soil stabilizers, crop sprays, and seed coatings. It is not hazardous to the environment, it breaks down in nature to other inert substances over a time span of a few months. It evaporates into the air leaving little or no residue. The U.S. Food and Drug Administration has also given wide approval for the commercial uses of PEO including as an ingredient in denture adhesives, cosmetics, soaps, and detergents, use as a coating of or ingredient in pharmaceutical tablets, and as a foam stabilizer for beer. A Mine Safety and Health Administration (MSHA) inspection determined that there were no measurable toxic substances or carcinogens associated with the usage of PEO in mining operations including blasting preparation, drilling, loading of ANFO in blastholes, or after blasting.
Mining-industry; Mining-equipment
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Minneapolis, MN: U.S. Department of the Interior, Bureau of Mines, TN 392
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division