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www.rockproducts.com Frac Sand Insider May 2015 | 51 Geology Substitutes for natural frac sand include resin-coated sand and manufactured proppants such as ceramic beads made from mate- rials obtained from sintered bauxite (Beckwith, 2011; Dolley, 2012). DEVELOPMENT OF ALTERNATIVE PROPPANTS Resin-coated sand Proppants manufactured as resin-coated sand are touted as being better-performing than "Northern White" sand as to per- meability, conductivity, crush resistance, and reduced fowback in a variety of temperature and pressure conditions (Preferred Sands, 2012). The compressive strength (crush resistance) of the grains is increased by the resin coating, which shields the grains from fracture closure stresses, prevents shattering, and contains any fnes produced (Pallanich, 2013; Fairmount San- trol, 2014). Another advantage of resin-coated proppants is that they can be made available in a range of mesh sizes (Preferred Sands, 2012). Resin-coated sands consist of less-optimal sili- ca sand, as a substrate (seed), that has been coated with ei- ther phenolic or non-phenolic resin to reach the desired shape, grain size, and other properties. According to a manufacturer of proppants using non-phenolic resin, these proppants are envi- ronmentally "greener," as they require less energy to produce, and are more cost-effective than the phenolic resin-coated prop- pants (Preferred Sands, 2012). Resin coatings can be either pre-cured (bonded before going downhole) or curable (bonds grains together in response to high downhole pressures and temperatures) to minimize or prevent proppant fow-back (Beckwith, 2011; Pallanich, 2013). Curable resin treatments can be applied to both sand and ceramic proppant (Beckwith, 2011). synthetic PRoPPants Ceramic proppants are manufactured from nonmetallurgi- cal bauxite or kaolin clay that is sintered (powdered and baked in high-temperature kilns) to reduce water content and increase density, roundness, and strength (Beckwith, 2011). In this process, the sin- tered bauxite is mixed with additives such as aluminum oxide, silicate, and iron-titanium oxide (ShanXi GuangYu Ceramic Proppant Compa- ny, 2012). Despite their higher cost compared to natural frac sand, ceramic proppants are more homogenous in composition and more uniform in size and roundness, giving them a higher fracturing strength in wells at greater depths and higher pressures, and they have greater conductivity than either natural frac sand or resin-coated proppants (ShanXi GuangYu Ceramic Proppant Company, 2012). The manufacture of synthetic proppants relies upon natural re- sources of aluminum-rich minerals that include bauxite, kaolinite, alunite, and halloysite (Rupke, 2014). Because the production of alumina on a commercial scale in the United States relies almost entirely on its recovery from bauxite (Bray, 2014), the synthetic proppant industry is dependent upon the domestic and global sup- ply of bauxite. Nearly all of the bauxite consumed in the United States is im- ported, and there is no government stockpile (Bray, 2014). The world bauxite resources are estimated at 55 to 75 billion tons, and are distributed on the following continents: Africa (32%), Oceania (23%), South America and the Caribbean (21%), Asia (18%), and elsewhere (6%) (Bray, 2014). The principal countries from which the United States imports both bauxite and alumina are Jamaica, Brazil, Guinea, and Australia (Bray, 2014). Additional countries that mine bauxite are China and India (Beckwith, 2011). Potential non-bauxite sources for alumina in the United States might include clay, alunite, and anorthosite (Bray, 2014). Kaolin (an aluminum silicate clay mineral) deposits in central Georgia are the principal U.S. sources of kaolin, accounting for 92% of domestic production (Virta, 2014). CARBO, a ceramic proppant producer, has a facility in Toomsboro, Georgia (Plate 1), that is close to these kaolin sources (Beckwith, 2011). Globally, countries with substantial resources of kaolin include Brazil, Bulgaria, France, the United King- dom, Iran, Germany, India, Australia, Korea, China, and the Czech Republic (Beckwith, 2011). As the synthetic proppant industry grows with advancements in technology, the suitability of alternative raw materials such as coal waste and oil shale, is being explored (Bray, 2014). One example of success in this effort is credited to an engineered proppant developer at Penn State University, referred to as Nittany Extraction Technologies Company (NETCo), whereby it is using waste material that includes glass, alumina silicate mine tailings, fy ash, metallurgical slags, and rock cuttings from oil and gas drilling as raw materials in the manufac- ture of its ceramic proppant (Beckwith, 2011).