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The year was 1983, and I was working as an editorial assistant at a petroleum magazine. One of my jobs was to mark up the manuscripts for typesetting, then send the printed galleys to the proofreaders. One particular article came back with a testy note.
“THERE IS NO SUCH WORD!” the proofreader had written. “IT IS NOT IN ANY DICTIONARY.”
The word, circled in red every place it occurred, was “proppant.”
By the early 1980s, the term had actually been around for over 15 years, but it’s not surprising that a proofreader couldn’t find it in the old musty dictionaries from the company library. Before mid-1960s, the operative phrase was “propping agent.” I can’t discover who coined the word “proppant,” but the term seems to appear all at once in several magazines in 1966.
Keeping the cracks open. Fracturing with explosives and other forms of applied pressure has been used in wells of all kinds since the late 19th century, including oil, gas and water wells. The deeper the well, the more insistent an induced fracture will be about closing back up. Methods of keeping fractures open, with both acid and sand, have existed since the 1930s.
Proppants have always been a required component of hydraulic fracturing, but their use has evolved steadily since the first experimental frac job in 1947, which utilized sand from the Arkansas River. I don’t know how good the sand was on that first frac, but they’ve improved since then. Some varieties of silica (quartz) sand make an almost ideal proppant. The highest-quality sand tends to be naturally spherical, corrosion-resistant, extremely strong and as cheap as … sand.
Ordinary, angular sands dredged up in rivers or scooped up from beaches are not very useful as proppant, however. The best natural frac sand is produced from high-purity sandstone. It can be sorted into sizes ranging from 0.1-mm diameter to over 2 mm, depending on requirements, although most of the proppant sand used today is between 0.4 and 0.8 mm in diameter.
Potential sources of good-quality proppant sand are St. Peter sandstone, Oil Creek sandstone, Jordan sandstone and Hickory sandstone, among others. These particular stones are composed of quartz grains that have been through many weathering and erosion cycles, which has removed almost all minerals other than quartz, and produced grains of particularly round shape. They are usually soft and poorly cemented, which allows them to be excavated and crushed with minimal damage to the quartz grains.
Traditionally, Wisconsin and Texas supplied much of the proppant sand used in hydraulic fracturing. However, surging demand has inspired many companies from different regions to get into the sand business. Most of the more recent players are located in the central U.S., particularly the Midwestern states, where St. Peter sandstone deposits are close to the surface and easily mined. Today, almost 60% of frac sand is produced in the Midwest.
Manufactured, uncoated ceramic proppant was first used in 1983. The particles made from sintered aluminum ore displayed many improved qualities—greater crush resistance, improved spherical shape and uniformity. They were also more expensive, but improved well production due to better interparticle (interstitial) space, which usually justified the added cost.
The very qualities that make proppant flow easily are the same ones that make it flow back out again. Proppant flowback can begin immediately, along with fluid flowback, as soon as fracturing pressure is released, and may continue throughout the life of the well. This is bad for two reasons: reduction of hydrocarbon flow, leading to decreased well revenue, and potential equipment damage, leading to increased intervention cost. Damaged tubulars, wellhead assemblies and valves can add considerably to the overall cost of a well.
Resin-coating was introduced to proppants to help mitigate flowback, but did not find widespread use until the mid-1980s. Both sand and ceramic proppants can be resin-coated, but in general, resin-coated sand occupies a middle position between raw sand and ceramics, offering performance improvement over the former and cost advantages over the latter.
Proppant uprising. As the shale revolution rolls forward, demand has grown from modest to strong to truly staggering. U.S. demand for well stimulation materials, including frac sand, is forecast to rise over 10%–12% a year during the next several years. Estimates of total proppant demand in North America by 2017 range from 55 billion lb to 100 billion lb per year. Sand is expected to continue dominating volume sales, with faster increases in resin-coated products. Demand for ceramic proppants will also continue to grow rapidly, although traditional manufacturers of ceramic proppants have faced increasing competition from China, where cheap bauxite is plentiful. There is also competition from lightweight proppant types, such as walnut shells and crosslinked thermoplastics.
High oil prices have caused the fastest growth to be in regions with the most liquids potential, including the Permian basin and the Eagle Ford shale in Texas, the Marcellus shale in the East and Utica shale in Ohio, and the Bakken region of North Dakota. Longer-term, as natural gas prices strengthen (with the growing possibility of future U.S. LNG exports) then proppant demand will increase in the more fallow gas-prone areas of the Haynesville and Woodford shales.
Perhaps the biggest question mark lies over California’s Monterey shale, considered by many experts to hold very large reserves of light oil. A major push to develop these unconventionals will put even greater pressure on both natural and manufactured proppants in coming decades.
To meet the demands of the coming decades, the proppant industry will require both improved materials and smarter engineering. But the operative word is still going to be “volume.” 
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