Q&A: Challenges of Sand, Solved

Published on April 4, 2023
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Learn how Sandtinel technology optimizes separation and prevents equipment degradation in this Q&A with Chris Johnston, Lead CFD Researcher at Sandtinel.

Q. Let’s start with the basics - what is sand?

A. Sand is a blanket term that covers a wide range of different types of granular solids. Most sand has a big component of crystalline silica, or quartz.

Q. What are the different types of sand and why is it important to know what type you’re working with?

A. There’s all sorts of different types of sand, like river sand taken from river banks, concrete sand made from crushed concrete, and even manufactured sand which production companies smash and crush from larger rocks. We are most interested in frac sand which is made from high purity sandstone, and is pretty pure crystalline silica, or quartz.

The biggest difference with frac sand compared to other grades is that it doesn’t have other types of rock and mineral mixed in – those are usually less durable than quartz, so the more pure frac sand doesn’t break down as easily in the fracturing process.

Q. Why and how is sand used in the fracturing process?

A. In the fracturing process, frac sand is mined before it’s transferred to a wet plant to remove all the silt, debris, and other contaminants from it. It gets dried and screened in a dry plant before being sent to site. During the drilling and completion process, a rig drills a hole several thousand feet down, then turns 90 degrees and drills through a layer of shale; this is the wellbore. A pressurized mix of water and frac sand are forced into the well which fractures perforations in the shale layer. This releases hydrocarbon liquids which flow up the wellbore to the surface.

Q. Is there a difference between the sand that’s in-situ and sand used in the fracturing process?

A. There definitely is. There’s a mix of sand that returns to the surface along with the oil that needs to be safely and effectively separated. The frac sand is usually high quality and very hard so it maintains its shape well. If it’s coated in resin during its production process, it will be even more durable to stand up to large stresses. However, that’s not the only source of sand in the mix. There’s also formation sand that breaks off underground which can come up through the wellbore as well. This is usually based on the geographic region, and it has all the impurities and other minerals which are screened out of frac sand. This formation sand usually breaks down a lot more, getting crushed up and broken into needle-like fragments.

Ultimately it is a mix of frac sand and formation sand which we need to deal with for sand removal.

Q. What makes sand challenging to work with/remove?

A. Sand has a tendency to get everything and can be extremely abrasive, especially at high velocities. Once it gets into your system it will accumulate everywhere – strainers, tanks, elbows, seals – and pretty much anywhere else the fluid touches.

Sand is measured in “mesh size” which is sort of like the fineness of a filter that would let the sand pass through it. But in reality any given sand blend has a huge range of different sizes. Knowing the frac sand blend (often 100 mesh) doesn’t tell you what size the formation sand is that’s coming back, nor does it tell you how the sand might have broken down during fracturing.

One of the challenges we face is that as sand has grown in demand, companies use whatever sand is available instead of the perfect grade of frac sand. This lower quality sand causes issues with removal afterwards. Smaller sand, getting down to “fines,” can be really challenging to remove by mechanical means (without the use of a filter and without external power, chemicals, etc). Bigger sand causes more damage, but smaller sand is harder to catch because it builds up everywhere and can be expensive to remove.

The trends we have seen are for producers to try to open their wells more aggressively and as quickly as possible because that’s been seen to maximize production. However, that also often ends up pulling more sand out of the wellbore, which needs to be effectively dealt with on the surface before it wrecks all of your equipment.

Q. What are the risks that come with sand separation?

A. Sand separators are safe pressure vessels as long as they are built and maintained properly, and receive regular NDT to ensure their ongoing integrity. The biggest risk is that it might not work effectively for you to remove the sand you’re hoping to remove. Other problems that can arise include:

  •  Fugitive emissions released during dump processes
  •  Plugging up with sand so that it can’t be cleaned out
  •  Experiencing high back pressure holding back your production
  •  Slugging and surging in the separator causing a cyclical “pull” on the wellbore which increases the sand production

Q. How does Sandtinel technology mitigate these risks?

A. Sandtinel sand separators have a very wide operating curve to match the operating conditions over the entire lifespan of a well so that you don’t need to be constantly changing out separators or inserts. There are no sacrificial elements like filters to replace or any external power requirements, making it a very simple piece of technology to incorporate into your process.

Sandtinel spheres provide high separation efficiency, targeted at a minimum of 95% sand removal for sand of 100 mesh and larger. Fugitive emissions are extremely low on Sandtinel separators as a consequence of the Vapor Lock technology in the vortex separator design. They also experience a very low back pressure and do not pull on a well, resulting in a sand separator that gets out of your way and lets you operate your well the way you want to.

Sandtinel spheres experience a very low back pressure and do not pull on a well, resulting in a sand separator that gets out of your way and lets you operate your well the way you want to.

Q. How does sand affect the degradation of equipment?

A. There are different approaches to dealing with the risk of sand erosion but some producers have given up on finding a sand separator that will really work for them, because there have been so many false promises in this field in the past. In fact, it’s common for sand separator vendors to just claim 99% or 100% sand removal with no data and nothing to back that up.

We’ve done some modeling to understand the effect of sand on erosion for pipe walls. It’s hard to quantitatively prove how effective sand separators are, so it doesn’t become apparent that these are false promises until you see the damage afterwards. This is why we are so excited not just to bring a new sand separator to the market which can handle the modern flowback environment, but to be able to prove it with extensive case studies, modeling, and data collection in the field.

This is why we are so excited not just to bring a new sand separator to the market which can handle the modern flowback environment, but to be able to prove it with extensive case studies, modeling, and data collection in the field.

Q. What happens to the sand once it’s been separated?

A. That depends on local practices and regulations. But in general, sand collects inside of a Sandtinel separator until it’s drained. The liquid sand slurry is sent to a downstream holding tank, or blowdown tank. We can use load cells and/or guided wave radar to monitor the collected sand, and then when it’s full, you would get it emptied out and disposed of safely.

Q. What makes Sandtinel spheres unique from other separators?

A. Sandtinel sand separators are a style of “vortex separator” which use patented Vapor Lock Technology to isolate gas in the upper hemisphere of the vessel. They’re radically different from other spherical separators which typically use a deflector baffle to try to knock sand out of the incoming fluid. By temporarily isolating the gas, we drastically slow down the liquid which has the sand entrained inside of it, providing a really long settling distance and retention time in a pretty small footprint (our separators are typically 48” inner diameter spheres). The Vapor Lock system also significantly reduces fugitive gas emissions during dump operations compared to other sand separators and experiences very little back pressure across the unit. Sandtinel separators provide the highest sand separation efficiency possible using mechanical means, aiming for a minimum of 95% sand removal at a sand size of 100 mesh and larger, over a broad operating envelope.

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