How to select your first crush stress – Lonquist Engineering

When testing a promising sand sample on a budget, it can sometimes be tricky to figure out where to select an initial crush stress.

If you are on a budget, selecting the initial crush stress for testing your sand sample can be tricky. Evaluate the API recommendations along with what sand is selling in the market.

Let’s say you want to evaluate some 100 mesh sand that you found, to see if it can become frac sand.

API has recommendations in their Recommended Practice (RP) 56 for the stress where you can start frac sand crush testing, and the suggested maximum fines percentage you should get.

For instance, they recommend you initially crush 20/40 sand at 4,000 psi (4K) and get a maximum of 14% fines.

And for 100 mesh (typically between 70 and 140 mesh sieves) frac sand, they recommend you crush at 5,000 psi (5K) and get a maximum of 6% fines.

If we check a brokerage website (like the gold standard DownHoleTrader.com), we see that 100 mesh is selling in the 7K to 13K range (as I write today).

Remember that K value is not a defined spec by ISO or API.

It is a market driven metric, so that the buyer can compare “apples to apples” when purchasing frac sand.

K value refresher, if you want it:
* For K value crush testing, we crush at a variety of stresses (we may start at 5k and then shift up to 8k, 9k, 10k, etc.) in order to determine at what point we exceed 10% fines by mass.
* That stress is the K value.
* For instance, a 9k sand may be producing 9.4% fines at 9,000psi, and 12.5% fines at 10,000psi. Because it exceeded 10% fines when we went to 10k, it is only a 9k sand.

To find out if your sand sample is even in the ballpark of frac sand strength, check the brokerage websites to see what K values your frac sand size of interest is selling at.

Now, back to this 100 mesh sample, where do we crush at? If it’s an initial evaluation of sand, we’re really interested in whether the sand is even in the “ballpark” to make it into the frac sand market.

Crush testing is really the most objective test we can do to evaluate the marketability of your sand.

Here is a breakdown of the guidance:
1. API recommends crushing 100 mesh frac sand at 5,000 psi (5K), and you should see less than 6% fines by mass
2. The industry (as per DownHoleTrader.com) is buying 100 mesh frac sand in the ranges of 7K to 13K

My recommendation here (which the client ended up going with) was to crush at 7K.

That way, we can see if the sand is at the minimum threshold for being marketable.

And if it is, we can launch into K value crush testing from there! We will also give you in-lab credit for having paid for the initial crush.

This is just one of the ways we work with you and do our part during these days of low oil prices and cutting costs.

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