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.

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.

MS Industries Provides a New Source for Microproppants

Russellville, Alabama

MS Industries (“MSI”), is a mining and mineral development company and direct mining source located in Russellville Alabama, is a primary producer of a wide array of industrial silica products along with frac sand and silica flour for the oil and gas industries.  MSI is now offering (>99% SiO2) “Super 100” whole-grain microproppants to the oil and gas industries.  By utilizing Super 100, oil well production and lifespan increases with some recent testing and reports suggesting microproppant addition can increase oil well production up to a 15% -30% over a 12-month period.

“In recent years, microproppant use has been shown to increase production and provide additional benefits in oil well operations”, says John Christmas, COO of MSI.  “One of the biggest obstacles was where purchasers could find a consistent and quality supplier of whole-grain microproppants, that is, until now”.

It has been known that proppant selection has changed over the years, as the industry has continued to investigate and utilize smaller frac sands to increase well production.  As the oil and gas industry grows and evolves, more companies are looking into methods for increasing production and life of the wells. The introduction of whole-grain microproppants into the fracturing fluids allows the secondary fractures to be stimulated thus allowing the secondary fractures to remain open upon pressure drawdown.  This allows for the user to access all the wells potential and maximize the reservoir capacities.

MSI’s Super 100, carries up to 25% whole-grain microproppant with particles ranging in the -150 mesh to 325 mesh size.  Super 100 is available direct from MS Industries as are all its industrial silica products and silica flour.

For more information please contact Brian Pace, MS Industries, 256-383-6740.