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Going with the grains

Drilling and completions practices have driven demand for frac sand to new highs and threaten shortages in some prime shale regions. But what qualities make a sand suitable for fracking, and where is the industry looking for solutions to supply chain challenges.

The North American shale boom owes its success to the hydraulic fracking techniques that unlocked previously inaccessible hydrocarbons.

And successful fracking depends on proppant — in most cases quartz sand, which is suspended in water and chemical solutions and pumped into the fractured formation.

While exploration and production companies have been fracking for decades, the practice has increased exponentially in the unconventional gas rush — as has consumption of frac sand.

Analysts at Credit Suisse project demand for frac sand to surge to 73 million tons in 2017, up 30% over the 2014 peak in demand.

cropJay-Zambito.jpg  Photo: Wisconsin Geological & Natural History Survey

"All of the factors that make for an ideal frac sand are met in western Wisconsin."
Jay Zambito, Wisconsin Geological & Natural History Survey
 

The spike is due not only to a significant rise in the number of completions but also to the type of wells being drilled in the shale plays - very long horizontals completed with high-intensity fracturing.

According to a recent report by consultant Energent, part of the Westwood Global Energy Group, most new completions in the Delaware basin use on average 1990 pounds (903 kilogrammes) of frac sand per foot, a rate that has more than doubled in three years.

With lateral lengths increasing – many horizontal wells in the Bakken now exceed 10,000 feet – and more multi-well pad drilling, some service companies are warning of a looming shortage of frac sand, specifically the sand compatible with the 40/70 mesh completions popular in the Permian basin, Energent says.

Proppants injected into the channels created by hydraulic fracturing must be strong enough to keep the fractures open after the fluid pressure is released, spherical enough to allow fluids to flow through, and within a size range that corresponds to the type of completion used in a well.

Synthetic ceramic proppants can be manufactured to a set of specifications and are particularly well suited to extreme high-pressure conditions. But frac sand is more economical and therefore far more widely used.

Frac sand is categorised by mesh size, based on the number of openings in one square inch of the sorting sieve.

For example, a 30/50 sand has grains small enough to pass through a primary mesh with 30 openings per square inch, but are captured by a finer secondary screen that has 50 openings per square inch.

SandMine1.jpg FRIABLE: Sand deposits in Wisconsin consist of the Ottawa White quartz sand ideal for fracking operations.  Photo: Wisconsin Geological & Natural History Survey
 

According to the US Geological Survey, 20/40 and 30/50 frac sands are most often used in oil reservoirs, while gas fracking uses finer grains of 40/70 and 70/140.

The upper Midwest has emerged as the US’ main source of “ideal” frac sand - Northern White or Ottawa White 99.8% pure quartz sand, with strong and spherical grains of desirable circumference.

Moreover, the sandstone deposits are near the surface, making them less costly to mine than deeper formations.

“The sandstone in Wisconsin that is the primary target for frac sand is Cambrian in age, deposited approximately 500 million years ago,” says Jay Zambito, a geologist and frac sand specialist with the Wisconsin Geological & Natural History Survey, a state-funded office affiliated with the University of Wisconsin — Extension.

“The depositional environment at that time in the upper Midwest US was a shallow sea and, on the shoreline, there would have been a desert with large dunes.

CropMike-Parsen.jpg  Photo: Wisconsin Geological & Natural History Survey

"One of the advantages here, whether it’s mining or agriculture or tourism, is the abundance of water sources. "
Michael Parsen, Wisconsin Geological & Natural History Survey
 

"The combination of wave action in a beach environment and wind-blown grain collisions in a desert environment results in deposits that are mineralogically mature, in that the grains that survive are primarily the hard, chemically inert mineral quartz. For that reason, most of the sandstone deposits in Wisconsin are quartz-dominated.”

Wind and waves conspired to bring out other desirable physical characteristics, Zambito says.

“The same depositional environment also sorts the grains by size, so there’s a very distinct size range in these deposits.

"The grains are also very well rounded and spherical. So you are looking at sandstones that have grains that are uniform in their minerology, their size and their shape. All those factors together make this an ideal proppant.”

Moreover, the western Wisconsin deposits are poorly cemented, close to the surface, and located near major transportation corridors, particularly rail.

“All of the factors that make for an ideal frac sand are met in western Wisconsin,” he says.

 

Mining

The preferred frac sand mine is an open pit quarry with minimal “overburden”, the topsoil and subsoil covering the sandstone, along with some undesirable bedrock.

Soils are stockpiled during mining and used to re-establish vegetation during the reclamation stage.

Undesirable bedrock overburden is commonly put back into the mine pit along with reject materials — clay, silt, and sand fractions that are either too large or small, and removed during processing — and used as reclamation fill, says Michael Parsen, a hydrogeologist at Wisconsin Geological & Natural History Survey.

Once exposed, the sand is removed with large excavators or power shovels. Miners prefer friable, or poorly cemented, sandstone, which can be easily scooped out and sorted.

The raw sand is washed, dried, screened and sorted by size. Tightly aggregated sandstone may need to be broken down by crushing, high-pressure water-jetting or grinding.

Sand that is unsuitable for fracking, such as miniscule grains known as fines, may be sold for other uses or used as infill when the mining site is reclaimed.

Handful.jpg CRUSH STRENGTH: High-quality frac sand is almost pure quartz, with spherical grains of nearly uniform size.  Photo: Wisconsin Geological & Natural History Survey
 

As with any mining operations, there are environmental concerns about frac sand extraction. Regulations vary state to state in the US but generally address air quality, land restoration and water usage.

Implementing those rules can be challenging, and environmental issues could become more prominent as applications for new mines grow in number.

Mines tend to be in rural areas, where local officials are charged with administering state rules.

“There can be challenges there, as rural counties with fewer resources are charged with overseeing many aspects of this rapidly expanding industry” says Parsen, who specialises in groundwater issues.

“It can often be a little bit of a learning curve for counties and sand mining operators alike to understand, adapt, and stay in compliance with regulatory rules.”

Wisconsin has a leg up in one environmental respect, he says. “One of the advantages here, whether it’s mining, agriculture or tourism, is the abundance of water sources.”

Precipitation on the order of 30-35 inches per year, Parsen adds, can also lead to unauthorised storm water discharges to local streams and creeks.

SandMineDryPlant TWIN PEAKS: Excavated sand is washed, dried, screened and sorted by size.  Photo: Wisconsin Geological & Natural History Survey
 

However, abundant water is not a feature in other parts of the country where frac sand mining is on the rise.

Exploration and production activity is ramping up in the Texas Permian basin, where fracking operations have traditionally been conducted, in large part, with sand from Wisconsin and Minnesota.

But with Permian crude oil production reaching 2.4 million barrels per day in May this year, a total that some experts believe will reach 4 MM bpd by 2021, demand for frac sand mined closer to the West Texas shale plays is increasing.

Credit Suisse says Texas mines could increase capacity by 32 million tons per year by the end of 2018.

While the Texas sand has a lower crush strength than Wisconsin’s, it serves the purpose — and is readily available and much less expensive because of reduced transportation costs.

Groundwater usage in the historically drought-prone region is already under scrutiny due to fracking.

Those concerns could increase as the Permian frac sand juggernaut picks up steam.

Meanwhile, operators and service companies will be grateful for new links in the frac sand supply chain.

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