Roundness, Sphericity and Microproppants

Gravel, sand, and other aggregates must be separated and classified based on their sphericity and roundness to determine the suitability for various applications.  These two terms describe the shape of these materials in two different dimensions.

• Sphericity measures how close the rock is to a perfect sphere.
• Roundness is a measurement of the edge of the rock.

These measurements provide a means of documenting the difference between various shapes, such as rhombus and a football, or a circle and an octagon. The mathematical equations for determining roundness and sphericity can be found here. 

The Krumbein Roundness and Sphericity Chart

Most applications for aggregate don’t require the level of accuracy provided by the above mathematical calculations, so a simple visual test is easier and faster. The Krumbein Roundness and Sphericity Chart has been widely adopted as a visual method for determining the shape of an aggregate. This chart can be seen in Figure 1.

Applications in the Oil and Gas Industry

Measuring sphericity and roundness is critical for fracking operations in the oil and gas sector, as these properties determine the strength and permeability of the aggregate. Silica sand’s ability to withstand high compression stresses depends on both of these factors. If the sand is on the low end of the sphericity and roundness chart, the particles will have too many sharp edges. 

When compressive forces are applied directly to those edges, the stress concentrations increase exponentially. If the sand is under too much stress, it will shatter, further increasing the amount of jagged-edged particles. This process can have a domino effect until nothing remains but a vein of silica dust deep in the ground.

Silica sand serves two purposes in fracking:

• It acts as a proppant, which props open the cracks in the shale.
• It allows oil to flow back to the well head.

Fracking sand must remain permeable or it has the opposite of its intended effect. Without gaps between the grains of sand, oil cannot flow between the particles. If the silica turns to dust, it instead blocks the flow of oil.

Microproppants

Sand particles smaller than U.S. Sieve size 140 mesh are referred to as microproppants. There are smaller silica products known as silica flour, but these flours are ground into dust and rate very low on the sphericity and roundness chart. Silica flour is too jagged and has very low crush strength. 

As a visual reference, imagine stacking basketballs. The rounded edges of the balls provide space for fluid to flow between each ball. Silica flour is more like stacking Legos. There is no space to allow oil to flow back into the well head between each “Lego.” See Figure 2. 

For fracking, it’s important to source silica sand that is still whole-grain rather than ground or crushed, ensuring that oil will still be able to flow between the grains. Figure 3 below is a photo of 200-grain mesh whole-grain silica sand. The dark column is a 0.7 mm pencil lead as a size reference.

These whole-grain microproppants rank much higher on the sphericity and roundness chart, and thus feature a higher crush resistance than ground silica flours. This ultimately adds to the productivity and service life of the well.

Silica Products From MS Industries

MS Industries provides high-quality whole-grain silica products for use in oil and gas applications. Our silica sand features consistent size, color, chemistry, ensuring reliable well performance with an optimal service life. For more information about our silica sand products, please contact us or request a quote.

API Frac Sand Standards and Microproppants

Recently, smaller grains of sand are in demand in the oil and gas markets. While fracking processes started with coarser grains of sand, the market is trending toward finer mesh size silica grains. 

At first, fracking used silica sand with mesh such as 16-30, 20-40, and 30-50. In the years since, however, the markets have made 40-70 and 70-140 mesh sizes the default standard. In this article, we’ll discuss the role of frac sand and other proppants in the oil and gas markets, as well as what the industry can expect in the race to mine finer silica sand. 

What Is Frac Sand?

Frac sand is a particular type of sand that’s used in hydraulic fracking. Shale and other low-permeability reservoirs may have relatively low amounts of fossil fuels, but they have enough to be increasingly viable in competitive oil and gas markets. Both oil and natural gas markets use frac sand to prop open wells to produce natural gas, oil, and other energy-rich fluids from fracking sites. 

Frac sand, which is crystalline sand derived from high-purity sandstone, has unique properties that oil and gas producers need. The quartz grains are naturally occurring, crush-resistant, and come in an extensive range of grain sizes for different operations. Frac is purely silica quartz, whereas other sands—like most intercoastal sands—are a mix of multiple different rocks and minerals.

Ultimately, silica sand offers highly consistent resistance to crushing and physical force to a degree that other sands can’t provide.

Proppants in the Oil and Gas Markets

Fracking processes break open shale reservoirs to extract natural gas, oil, and natural gas liquids. Once a site has been discovered, companies shoot highly pressurized jets of water into the reservoirs to create cracks and extract fossil fuels from the pores of the reservoir. 

Because these cracks are under tremendous pressure from the surrounding rocks and earth, they will reseal as soon as water pressure diminishes. That’s where silica sand and other proppants come in: the material fills the widening crack to hold it open, even when the water jet moves on. This allows oil and gas companies to continue collecting material from the well for as long as possible. Because silica sand is resistant to crushing, the reservoir can’t easily reseal, and companies can more efficiently collect fuel for processing.

The Impact of Mesh Sizes

Frack technology is continuing to grow and evolve, and so is market access to increasingly specific varieties of silica sand. Companies are gradually shifting to prefer finer grains of frac sand. 

Sand is measured through standardized sieve meshes that allow grains of different sizes through for sorting and categorizing. At first, larger mesh sizes, and correspondingly coarse sand grain sizes, were sufficient to mete out sand that allowed companies to extract fossil fuels from shale reservoirs. 

Today, many companies use advanced fracking practices and smaller grain sizes to increase the proppants’ grip in the reservoirs and collect more fuel. Finer sands allow companies to both increase daily barrel production and pull from the same well longer. 

407-0 and 70-140 grain size silica sand can push deeper into fine cracks and gaps in shale. Once the sand locks into place, it can hold the crack open and continue to wedge deeper into the shale. 

How can finer sand go deeper into the well?

Because fracking uses pressurized water to form the cracks in the first place, the addition of sand quickly forms a slurry. This slurry is slow, thick, and unable to reach into every crevice of the new cracks. Finer sand, however, is more resistant to forming a thick, slow slurry. It has a better Settling Velocity Rate (SVR) and goes deeper into cracks before the velocity decreases.

Not only can companies reach deeper into a reservoir, but the finer sands increase overall surface area coverage of the shale cracks. The bigger the area of exposed pores, the more natural gas, liquid, and oil the company can extract per day and per well.

Frac Sand Mining

Fracking processes rely on finely controlled water and sand to extract as much fuel as possible from shale and low-permeability reservoirs. The water creates cracks and empty spaces in the rock formations, and the sand props the gaps open for longer extraction windows. 

This sand demand isn’t negligible; each well requires up to 10,000 tons of sand. With the developing need for finer sand, the demand is also concentrating on just a few locations that can supply high-purity silica sand grains. 

One of the most reliable locations for high-purity silicon dioxide sand in the United States is the region at the border of Minnesota and Wisconsin near the Great Lakes. This region produces highly spherical silica sand that’s close to the surface and consistently high quality. 

Frac Sand From MS Industries II, LLC

We specialize in providing both high-quality materials and logistics management. Our team delivers silica sand at your company’s requested specifications and on time, every time. Contact our team today to learn about our frac sand solutions or request a quote to get your order started.

K-Value and Microproppants

It’s 4:00 am, there is a test in four hours. You still have to shower, make coffee, feed the dog, get the kids to school, and drive 45 minutes to the testing facility. That leaves you with 13 minutes and 27 seconds to understand proppants.

Don’t worry, there is only two things that you must know about proppants and why they work.

1. Proppants’ first job is to open the earth below and keep it open (“Prop” it open).
2. After the proppants accomplish the first job, their second job is to allow the gases and liquids to flow back to well head. They need to keep the well permeable.

Done with at least 6 minutes to spare.

Bad news, the world of proppants can be a lot more complicated than that. Good news, you don’t actually have to take that test.

One of the more difficult things about hydraulic fracking is understanding what is actually happening several thousand feet under the ground. Cameras do not work under those harsh conditions, and you definitely cannot send someone down to watch.

The easiest and most cost effective way of understanding things we cannot see is to model key aspects of the environment below the surface of the Earth.

One test mimics the pressures of 2-3 miles of dirt, rocks and water, ISO/API’s Proppant Crush-Resistance Test. This puts the proppants under different pressures and checks proppants’ resilience to these forces.

The test starts by prepping the proppants to make sure there are no particles smaller than a 200 US mesh screen. Then the sample of the proppant is placed onto a smooth steel plate within a cylinder. A piston is used to apply and hold specific pressures for two minutes. These pressures start at 2,000 PSI and step up every 1,000 PSI.

After performing the test, the proppants are sieved to see how many particles pass through the 200 mesh.

What does this show? Before the pressure was applied, the proppant sample was sieved, removing all particles smaller than 200 mesh. If any new particles pass through the 200 mesh sieve after the test, it was due to the proppant literally crumbling under the pressure. When the crushed, pulverized, and destroyed particles surpass 10% of total weight of the sample, the proppant is considered unusable at those pressures.

When the individual grains of the proppant crumble, break, and fail, they leave behind small broken glass-like pieces. These shards block the passage of the oil and gas through the proppant, not allowing the well to produce as much of the commodity as it could. Also, the irregular shape of the shards do not add any strength to the other proppants in the area. Meaning the other particles have to hold more weight. With the increased weight, the greater chance the other particles also crumble, break and fail. It becomes a feedback loop that causes less output in the real world.

Now enter microproppants. Microproppants are particles smaller than US Sieve 140 mesh. What else is smaller than US Sieve 140 mesh? US Sieve 200 mesh.

The ISO/API crush-resistance test removes would be microproppants before it can be evaluated. Making this test as-is, irrelevant to evaluate microproppants. The solution to adjusting ISO/API crush-resistance test would be to lower the sieve size to a US Sieve 270 mesh or 325 mesh depending on the microproppant.

Unfortunately, not everyone that makes decisions on the best proppant for their wells understands the ins and outs of this process. Those that depend heavily on ISO/API’s method to discern what is a good or bad proppant when looking at microproppants might miss out because of the bureaucratic nature of depending on specification sheets.

Another quagmire with microproppants as an emerging technology is silica flour. Silica flour is being pushed as a microproppant.

What is silica flour? Silica flour is where silica sand is crushed, pulverized, and destroyed in a milling process. Silica flour is the exact particle that ISO/API’s crush-resistance test looks for.

Silica flour fails at proppants’ first two jobs of holding open the shale and allowing the petroleum to pass through it.

When evaluating possible microproppants, look for wholegrain products. Ask for ISO/API results for the microproppant. If there are no results, it shows that the microproppant cannot pass the tests at any capacity.

Microproppants are a new and exciting development in the oil and gas world, but be careful when deciding what to use for the horizontal wells.